Soundman2020 - Studio Design Forum

Hello all,

It's time to get out of the bedroom!

I have been reading on the John Sayer's forum, (where I posted this same question and no one responded), as well as Rod's book for the past week or so, and have tried to research as many questions as I can before posting, but I have come to a point where I need some direction and advice. I have a carport on the side of my house. It looks like a single car garage from the front, but the exterior side and the rear are open into the yard, except for a small storage shed in the back (blue square). Rough drawings attached. The black rectangle is the garage door, the blue ones are standard doors, and the orange one is a double window.



The whole thing is under the main house roof and is on a concrete slab, so all that needs to be built are the side and back walls (and the wall in front of the garage door-see below). The storage shed needs to stay, as it houses a freezer and all my tools. I also want to use it for storage of guitar cases and my small PA speakers.

I record rock music mostly, and use an electronic drum kit to keep the volume down. Typically one instrument at a time. That being said, I wouldn't mind being able to record a real drum kit, or a full band, if it would sound good and work in this space.

There is a neighbor on the other side of the fence, so I do think the walls I build are going to need to isolate the studio some, but I also don't see me going on into the late night with recording. It's only me and the wife in the house, so I'm not too concerned with the wall between the studio and the house or the ceiling (1 story house, attic space above).

The central AC unit for the house is oversized in the first place, I consulted with an AC tech, and he assured me adding a vent or two into the studio was no problem.

This will mostly be for my personal use, but if it comes out good enough, I wouldn't mind trying to mix and/or record other bands and artists in there.

My budget is semi-flexible. I'd love to come in at $10,000. $15,000 is do-able. I can maybe talk my wife into $20,000 if I'm lucky! I'm also not opposed to using a design consultant, although I have no idea what that would cost.

Also, I'm a pretty handy guy who is familiar with standard construction, and I got a carpenter for a brother in law, so we can do a lot ourselves.

I'm assuming my best bet with this setup is a single room for tracking and mixing? I believe trying to carve up the space will result in inferior rooms for both. Maybe use movable treatments depending on the situation?

So, here's what I need advice on:

Shape:

My original idea is to build a 19' wall from the front of the garage to the shed, then build another wall from the front right edge of the shed to the house wall, making a perfect 19' x 12' 5" rectangle (Brown color) (the ceiling is a whole other can of worms I will address in a moment). Also I would add another doorway into the shed from the studio to use it for case storage and the like. I will also need to add an entry door on the side, so myself or other musicians can come and go from the studio without having to enter the main house first (doorway locations open for debate). And finally build a new wall in front of the garage door for sound isolation there as well. We will leave the garage door on the outside for looks (sealed, caulked, cemented, whatever it takes) as the entire house is brick and removing the door and closing it in would look odd in my opinion. See drawing #2. (wall in front of garage door not shown). I'm also thinking no windows, just to make it easy (and quiet).



Ceiling:

The garage ceiling is only 7' tall, however I went up and checked in the attic, the ceiling joists on the garage are independent of the roof and the main house, they are literally just holding up the vinyl siding & plywood on the garage roof. There is room to take the whole ceiling up another foot at the front and side edges, and up to 6' more as it slopes to the main house and the rear of the garage. I've attached an aerial view of the roof to try and show the pitch. (Garage is grey rectangle).



So the question for the ceiling, should I just make it an even 8' across and flat? Or should I use the space and make it gabled? Cathedral? A triangle from side to side? It's a little strange as it is sloped in two directions. I'm not sure my drawing gets the point across. Basically the roof from the front of the house and from the side pitch upwards. So perhaps a sunken type ceiling, where the perimeter height is 8' and going up as it heads to the center of the room?

I want to do this as good as possible and am open to any ideas, changes, whatever. We can move the shed, we can move doors, I'm thinking the mixing position will be facing the garage door, but I'm open. I still have a ton of questions about the actual construction (double walls, soffit mount speakers, treatment, slats, etc.) but I figure those are questions for the actual construction forum. I figured I'd better get an idea of what I want to do, then move over there for the how.

Thanks in advance for your replies and I hope I followed all the rules!

EDIT: I read a few more things since my original post and figure I need to address them. I read that isolation is an all or none option? So I cannot just do a double wall or a staggered stud wall on the outside walls and not deal with the walls between the studio and the house? I'm only concerned about the neighbor, and then only somewhat. Not making the walls airtight on the house side or ceiling also helps make the HVAC system easier as the whole room won't be an airtight thing. I also am trying to maximize the space as I will already lose about 1 foot of width when I construct the long outside wall. I didn't want to lose another 6" on the side wall side as well. I also realize my final dimensions will be smaller than the 12.5 x 19 area I'm showing. Once I have the construction figured out I'll adjust the length dimension appropriately. A quick calculation shows if I can do 15 x 11 x 8 I'm at a pretty good ratio. But if I do something with the ceiling, that may change (how do you calculate ratios with a variable height ceiling?)

All that being said, I'm not going to be one of these guys who ignores the rules, if I have to do it, I'll do it!

Hi Scott, and welcome to the forum! Very glad you found your way over here.

I have been reading on the John Sayer's forum, (where I posted this same question and no one responded), as well as Rod's book for the past week or so, and have tried to research as many questions as I can before posting, but I have come to a point where I need some direction and advice.

That's what this place is all about! Hopefully, we'll be able to help you.

Rough drawings attached.

Maybe you could add a couple of photos, so we get a better idea of what you are dealing with?

The whole thing is under the main house roof and is on a concrete slab,

Concrete slab is great! Do you have any details about the roof? How much height do you have available under that roof?

There is a neighbor on the other side of the fence, so I do think the walls I build are going to need to isolate the studio some, but I also don't see me going on into the late night with recording. It's only me and the wife in the house, so I'm not too concerned with the wall between the studio and the house or the ceiling (1 story house, attic space above).

You will probably still need to do all four walls and the ceiling to the same level, because acoustic isolation is only as good as the weakest link. So, for example, if you do very good isolation on your walls but not so much on the ceiling, sound will basically ignore the walls and get out through the ceiling instead. And once it is out, its out all over, not just in that direction. If it gets out through the ceiling, it will still get to your neighbor. Thus, even though you don't need good isolation on the house-side of your studio, you'll still need to have the same isolation there as the other sides, unfortunately.

The central AC unit for the house is oversized in the first place, I consulted with an AC tech, and he assured me adding a vent or two into the studio was no problem.

That's good news! It makes things a bit easier (and cheaper...) for you. One thing you might have to check back on, with your HVAC guy, is the increase in static pressure: You'll need silencer boxes (to allow the air to get through while blocking the sound from getting in or out), and those tend to increase the "static pressure" a bit, because of the convoluted path that is needed for the air. Once you have your design for those, you can run it by him, and see if he thinks the existing system will be able to handle that, or if you might need to add an extra fan somewhere, to take the load of the actual AHU.

My budget is semi-flexible. I'd love to come in at $10,000. $15,000 is do-able. I can maybe talk my wife into $20,000 if I'm lucky! I'm also not opposed to using a design consultant, although I have no idea what that would cost.

It seems that you will be aiming for a floor area of around 230 square feet, and with a budget of 20k, that works out to about US$ 87 per square foot. That's probably reasonable for what you have in mind.

Also, I'm a pretty handy guy who is familiar with standard construction, and I got a carpenter for a brother in law, so we can do a lot ourselves.

Also great! If your brother in law is a carpenter, the he has some tools. You also mentioned your own tools, so hopefully between the two of you, you have that covered. You probably don't need anything fancy in the way of tools: just normal stuff.

I'm assuming my best bet with this setup is a single room for tracking and mixing?

Tracking and mixing in the same room is a something of a conflict: the acoustic response you need for a control room is very well defined, and basically it needs to be absolutely neutral: the room should have no sound of its own, so that you can hear the direct sound from the speakers exactly the same as they are making it, without the room adding, subtracting, or "coloring" that sound in any way. That's logical when you think about it! But musicians find that type of acoustic environment to be rather dull, lifeless, and uninteresting. Not much fun to play in, as the room is just sort of "flat" and "boring". Musicians prefer a livelier sound, with the room providing some feedback for them: reflections, diffusion, a little reverberation, some ambience, ... that adds life to their music, and makes the instrument "come alive". The same applies to tracking the instruments: a good live room will have some "air" and "space" and "warmth" to it, that is picked up by the mics, so the instrument sounds more interesting, more "full".

So you have two very much opposite and totally conflicting needs. You can't mix very well in the type of room that sounds good for instruments, and you can't play instruments nicely in the "dry" acoustic space of a control room.

One solution is to just have separate rooms, with different acoustic in each. But as you figured out, you don't really have enough space to do that. The next best solution, is "variable acoustics". You design the acoustic treatment so that it is changeable in some way: things that slide, flip, rotate, open, close or etc. to expose different parts to the room, and thus achieve different acoustic response. So with all of the panels switched over to one extreme, the room response would be ideal for mixing, and with them flipped over to the over extreme, the room would be bright and airy for instruments that need it. And with the panels adjusted part-way in between those two extremes, you get great flexibility in modifying the room acoustic response to be whatever it needs to be for a wide range of tracking needs.

Here's some more information on how that can be done. http://www.digistar.cl/Forum/viewtopic.php?f=12&t=10

That's not too hard to do. It needs careful design, though, to make sure that you really will get the right response for both setups. But it's probably the best solution. Your room is a nice size, so you should be able to get it sounding good.

My original idea is to build a 19' wall from the front of the garage to the shed, then build another wall from the front right edge of the shed to the house wall, making a perfect 19' x 12' 5" rectangle (Brown color) (the ceiling is a whole other can of worms I will address in a moment). Also I would add another doorway into the shed from the studio to use it for case storage and the like. I will also need to add an entry door on the side, so myself or other musicians can come and go from the studio without having to enter the main house first (doorway locations open for debate). And finally build a new wall in front of the garage door for sound isolation there as well. We will leave the garage door on the outside for looks (sealed, caulked, cemented, whatever it takes) as the entire house is brick and removing the door and closing it in would look odd in my opinion. See drawing #2. (wall in front of garage door not shown). I'm also thinking no windows, just to make it easy (and quiet).

Sounds like a good plan to me.

The garage ceiling is only 7' tall, however I went up and checked in the attic, the ceiling joists on the garage are independent of the roof and the main house, they are literally just holding up the vinyl siding & plywood on the garage roof. There is room to take the whole ceiling up another foot at the front and side edges, and up to 6' more as it slopes to the main house and the rear of the garage. I've attached an aerial view of the roof to try and show the pitch. (Garage is grey rectangle).

OK, so ignore my question earlier about the ceiling height...

Be careful with those joists! They might seem to be there just to hold up the ceiling, but the actually do a lot more than that: they are part of the structural integrity of the roof: they prevent the weight of the roof from spreading the walls apart, and causing everything to come crashing down on your head... It is possible to replace them with something called a "raised tie" truss, or "collar tie" truss. I have done that in a couple of places for clients, and it works very well. It sounds a bit scary to be modifying your roof, but if it is done carefully, with the approval of a structural engineer, then its a great way of gaining plenty of extra height.

Basically, you add new joists that are tougher, a bit higher up, and you "sister" the rafters to add more integrity to the system, then you take out the old joists, and .. Bingo! You have a much higher ceiling! Here's some photos from one such build:

The original roof framing, inside:


New rafters and ridge beam in place:


New collar ties in place:


Completed, ready for sheathing:


This is definitely an option: a 7 foot ceiling is not good. Too low for a control room, and DEFINITELY too low for a live room. Instruments need space to sound good. Tracking instruments under a low ceiling almost never sounds good, for several acosutic reasons.

So the question for the ceiling, should I just make it an even 8' across and flat? Or should I use the space and make it gabled? Cathedral? A triangle from side to side? It's a little strange as it is sloped in two directions. I'm not sure my drawing gets the point across. Basically the roof from the front of the house and from the side pitch upwards. So perhaps a sunken type ceiling, where the perimeter height is 8' and going up as it heads to the center of the room?

Definitely gabled! It cant be cathedral, since you do need those collar ties to keep your entire garage together, so gabled is the way to go. Your structural engineer can tell you how much you can raise them and still be safe.

However, do be aware that this is going to stretch your budget a bit, and you might need to hire some extra help to do that, especially if your engineer says that you need a new ridge beam, as in the case above in the photos. Lifting that guy into place is not really something that two guys can do on their own.

I want to do this as good as possible and am open to any ideas, changes, whatever. We can move the shed, we can move doors, I'm thinking the mixing position will be facing the garage door, but I'm open. I still have a ton of questions about the actual construction (double walls, soffit mount speakers, treatment, slats, etc.) but I figure those are questions for the actual construction forum. I figured I'd better get an idea of what I want to do, then move over there for the how.

Right! The first order of business is to get your roof issue solved, then get the walls completed. Those will actually go together, since the new roof trusses will be resting on your new wall. Like I said, I've done this before, so I'm pretty much up to speed on how to do it, but you most definitely do need to get a structural engineer involved too. There's tensions and stresses involved, and playing with "very heavy things hanging over your head" should always be done with great care, and attention to safety.

I read that isolation is an all or none option?

Yup.

So I cannot just do a double wall or a staggered stud wall on the outside walls and not deal with the walls between the studio and the house?

Right. The general rule is: all sides done to the same level. There are some exceptions, or cases where you can bend that rule a little bit, depending on what you have, but you'll still need to have two leaves all around.

Not making the walls airtight on the house side or ceiling also helps make the HVAC system easier as the whole room won't be an airtight thing.

Simple rule here, and no way around it: If air can get through, then so can sound. Here's a graph I showed on another thread a day or two ago, that is sort of scary. It shows how much isolation you lose from having very tiny gaps, cracks or holes in your wall:



Its not very good resolution, but you an get the general idea. The top curve shows what happens if you have a gap equivalent to 0.01% of the wall area. The next curve down is if you have 0.02% gaps, the third curve is for 0.05%, and the fourth curve is for 0.1%. In other words the 4th curve shows how much isolation you throw away if your wall is 100 square feet, and you have a gap of about 1/10th of a square foot. In that case, if the wall was supposed to isolate to 50 dB, then it would only give you a bit less than 30 dB isolation....

That graph is a real eye-opener.

So yes, you do need to have complete, well-sealed walls around you on all sides.

I also am trying to maximize the space as I will already lose about 1 foot of width when I construct the long outside wall. I didn't want to lose another 6" on the side wall side as well.

There are techniques that can help avoid losing space while still having good isolation, but there are limits even then. In your case, you do have enough space that you can afford to lose a little off all sides, and still end up with a decent room.

Once I have the construction figured out I'll adjust the length dimension appropriately. A quick calculation shows if I can do 15 x 11 x 8

That would give you about 165 ft2 floor space, which is still OK. But I think it is possible to not lose that much! I don't think you need to lose 4 feet in length: probably no more than about 2 feet. And you can also get better ceiling height.

But if I do something with the ceiling, that may change (how do you calculate ratios with a variable height ceiling?)

Ahh yes! That's a problem. Because the room mode calculators that you find on-line (these are the two best ones; http://www.bobgolds.com/Mode/RoomModes.htm and https://amcoustics.com/tools/amroc ) only work for rectangular rooms. As soon as you angle any of the surfaces significantly, or add extra walls, then they no longer give valid results. There are techniques for dealing with that too, so you can estimate the modal response, but you also don't need to go crazy about ratios: Room ratios are just one of many, MANY aspects of studio design that you need to take into account. Don't sweat it if you can't get a "perfect" ratio, because actually there is no such thing! Just good ones and bad ones. As long as you are far away from the bad ones and reasonably close to the good ones, that's fine.

All that being said, I'm not going to be one of these guys who ignores the rules, if I have to do it, I'll do it!

I'd also suggest that you start modeling your room in SketchUp in 3D, as that makes it a lot easier to see how things fit together.

Your place has potential, for sure. I think it's worth putting the effort in to get the roof done so you can raise our ceiling as high as possible, and to make the final interior space as large as you can while still retaining enough isolation, then making the acoustic response variable, so it can both a control room and a live room, or anywhere in between, as needed.


- Stuart -

Thanks for your response Stuart. Been doing some more research, and have a few more questions.

I want to maximize the space as much as possible, but I don't want to under-isolate the room.

I just don't really know how much isolation I really need since the whole thing is open, I can't even really test anything with the DB meter until a wall gets built.

If I do double walls all the way around, then I actually end up with the room within room and can build my new ceiling on these walls as well. Whole room ends up at about 11' 1"wide x 17' 5" long. If I do something else, like staggered studs or whatever I may gain 6" or so on each side, probably not worth it.

Another issue is the doors. I'd rather not do the double door to the outside, but if I only do a single, no matter how dense and sealed, does it defeat the whole purpose of the double walls?

Now the roof, I've attached a few pictures.


As you can see the actual roof beams are resting on the 2x8 beams at the end of the house. The 2x4's in the joist hangers are what the garage ceiling is attached to, and it's the same on the opposite end, so no structural support of the roof whatsoever.

Here is what the roof pitch looks like from the outside


The roof both pitches in from the front and sides, so my new ceiling on the inside would end up like this, rather than just a regular gabled roof with a flat front and back.


Now at the rear of the room, I wouldn't necessarily have to pitch back down and could end at that wall with a flat triangle like a standard gable. (I hope that makes sense, I promise I'll start trying to get better with sketchup!). Would that be a good idea? Kind of make for a higher ceiling on the tracking end of the room, or should we keep it all symmetrical?

And finally, if I were to just get rid of the shed and side corridor and close the whole area in, the room would now be approx. 26' x 11'. Is that enough room now to split things up into a control room and a tracking room? Or is that small width killing me? Just wondering.....

I've got plenty more to read and ask about, but this will cover everything that kept me up thinking last night!

Thanks again,

Scotty

I just don't really know how much isolation I really need since the whole thing is open, I can't even really test anything with the DB meter until a wall gets built.

That's true: you can't test how much you are getting, but you can still determine how much isolation you need, in total. And you can also determine what the typical background ambient levels are around your place (so you know "how quiet you have to be", as well as determining how bad some of those outside noises might be, that you need to block: For example, if you are close to a road with heavy traffic, or an area where emergency vehicles often go around with their sirens on, or maybe a place where there's aircraft flying over frequently, or helicopters... or maybe just your neighbors have noisy dogs that love to bark loud day and night, or mow their lawns, or throw loud parties, or yell and scream at each other.... It would be good to get out your meter and try to measure all of those, since you would need at least enough isolation to silence those things (apart from considering how much you need to silence your own sounds going out...).

So its worth doing some testing with your sound level meter, just to get an idea of what you are dealing with, even if you can't yet measure how much isolation you are getting.

If I do double walls all the way around, then I actually end up with the room within room and can build my new ceiling on these walls as well.

Exactly! That is, indeed, the correct way to do a full "room-in-a-room" studio. You have the outer leaf, which is the shell of the building itself (in your case you nee to build some of that still), consisting of the floor slab, the walls, and the roof, all of which must have only one leaf in them. Then you build the actual "room" inside that, resting on the same floor slab, and consisting of the walls and the ceiling, once again with only one leaf, and with none of that touching the outer leaf. That's the ideal situation, but its not always possible to do that fully, for one reason or another, in which case there are "work-arounds" that you can implement to compensate for whatever the problem was. A vented roof deck is one such case. A garage door that cannot be removed is another. So are electrical panels that can't be moved, plumbing that has to be accessible, HVAC ducts that run through the room, fireplaces and radiators, staircases, and similar things.

Whole room ends up at about 11' 1"wide x 17' 5" long.

That's a decent size.... What about height?

Another issue is the doors. I'd rather not do the double door to the outside, but if I only do a single, no matter how dense and sealed, does it defeat the whole purpose of the double walls?

It is possible to do just a single extremely massive door, but I'm not a big fan of that: the mass you need is enormous (use the Mass Law equation to figure that out... its not very encouraging...). Such a door needs major structural framing additions just to hold it in place without sagging or bending the framing as it opens and closes, and is dangerous too: you don't want a door that weighs many hundreds of pounds slamming on your finger or foot! Nor do you want it slamming into the door jambs because you close it a bit too fast: there's enough inertia in that to damage the jambs, and therefore your isolation. If you need good isolation for your room, its much better to go with a pair of doors, back to back.

It's not that hard to build the doors yourself. Here's how to do that: http://www.digistar.cl/Forum/viewtopic.php?f=12&t=23

Now the roof, I've attached a few pictures.

I suspect that you might have a vented roof deck...

As you can see the actual roof beams are resting on the 2x8 beams at the end of the house. The 2x4's in the joist hangers are what the garage ceiling is attached to, and it's the same on the opposite end, so no structural support of the roof whatsoever.

Actually, there is! Even though the joists are not directly attached to the rafters, they still accomplish the same purpose; they prevent the weight of the roof from spreading the walls apart. Those joists are in tension, and they are carrying the load. You should call in a structural engineer to take a look at what you have, and let you know what can be done about it. Personally, I would suggest that you consider converting your roof to raised-tie: replace those joists with collar ties high up across the rafters, to carry the same load that the joists are carrying right now. Take a look at the photos I posted of the similar case I had to deal with a few years ago. But whatever you do, don't change anything in the framing there until you get a structural engineer to inspect it.

Now at the rear of the room, I wouldn't necessarily have to pitch back down and could end at that wall with a flat triangle like a standard gable. (I hope that makes sense, I promise I'll start trying to get better with sketchup!). Would that be a good idea? Kind of make for a higher ceiling on the tracking end of the room, or should we keep it all symmetrical?

That's fine! Having the ceiling higher at the rear of the room is a good thing, if you can do that. Having it higher all over is better!

Here's a photo from a different studio while it was under construction, with raised-tie trusses: you can see how the middle-leaf ceiling will have sloped sections on the sides, and the inner leaf will follow that (yes, this has to be a 3-leaf ceiling, because it is also a vented-deck roof)



Here's what it looked like with the middle-leaf sheathing partly done (just one layer of OSB) and the inner-leaf walls going up:



And here it is with middle-leaf sheathing completed:



You can see how those angles on the sides allow the center of the ceiling to be a lot higher than it could have been without the raised-tie trusses. Here's what those looked like, before the roof deck went on:



You have to have SOMETHING on the rafters like that, to prevent them spreading the walls, and themselves. A triangle is only strong if it has three sides: if one side is missing, it is not strong any more.

And finally, if I were to just get rid of the shed and side corridor and close the whole area in, the room would now be approx. 26' x 11'. Is that enough room now to split things up into a control room and a tracking room? Or is that small width killing me? Just wondering.....

That would give you nearly 290 square feet total, so you could indeed have a small control room and a small tracking room with that. The tracking room would be more like a large booth than an actual room (maybe 80 or 90 ft2), but that might still be big enough for what you need: as long as you don't plan to have a symphony orchestra in there! But decent for most instruments on their own. And if you use sliding glass doors between the rooms, you could even open those for tracking occasionally, when you need a bit of extra room volume for improve acoustics.

I've got plenty more to read and ask about, but this will cover everything that kept me up thinking last night!

- Stuart -

The more I read and research, the more confused I become. I need just a few more clarifications to decide on a final design. I played around with some different design ideas, tried some angular room shapes, tried to incorporate a sound lock (instead of double doors), and I keep coming to the same conclusion, that the room is just too narrow to really do anything other than a regular rectangle. I have decided to go ahead and remove the shed and use the entire area, which after creating the room with a room ends up at approx. 25 x 11. Ceiling high will be at least 10' in the center and 8' at the edges, maybe more (engineer is coming to look next week!). I am wrestling still with the idea of a one room studio or to do the small booth and separate control room, so the questions I have to determine the way to go are:

I will primarily be recording rock bands in here. The drums are going to be the main concern. Is a 90 ft2 "tracking room" big enough for a real drum kit, or would it sound better in an overall bigger single room with well designed variable acoustics?

If the drums would be better in the single room scenario, should I still build some kind of booth for either vocals or guitar cabinets? (maybe just a smaller one?)

Everything I read says the rear wall behind the mix position is sacred ground. But that's exactly where the door would need to go to get into the booth or room if I build it. I would assume the door would be dead center because the rear corners would absolutely need heavy bass trapping?

The door to outside, if I do double doors, the exterior door will open outward and the hinges will be exposed on the outside. For normal construction, that's never supposed to happen. Do the hinges need to be stainless steel or something similar so they don't rust in the elements?

How much does just the typical "stuff" in the control room affect the sound? For example, the electronic drum kit in the corner, the stack of small PA speakers in the other, the rack of guitars, assorted cases, amps, you get the idea. Should I try and plan for some kind of storage to remove those things from the room?

Lastly, I just read the 40 page epic post on John Sayer's forum where you built the studio with Frank. I didn't see any dimensions but his small corner control room, built to help create the biggest live room possible in the space caught my eye. Do I have enough space for a design like that? Or will the control room be too small?

I'm really wanting to create something special here that I can actually use as a semi-professional recording studio. Am I being unrealistic with the space I have? I just don't really know what the best design plan is, if you could point me down that road, I would be forever grateful.

The more I read and research, the more confused I become.

That's normal! Acoustics is a big subject: it takes a while to get your head around all of it, and start making sense of things.

I need just a few more clarifications to decide on a final design. I played around with some different design ideas, tried some angular room shapes, tried to incorporate a sound lock (instead of double doors), and I keep coming to the same conclusion, that the room is just too narrow to really do anything other than a regular rectangle.

Rectangular is, indeed, the best shape for most studios. It makes it easier to predict, easier to design, and easier to build. So that would make sense.

I have decided to go ahead and remove the shed and use the entire area, which after creating the room with a room ends up at approx. 25 x 11. Ceiling high will be at least 10' in the center and 8' at the edges,

That's great. That gives you some 275 ft2 of floor area to play with. For a single-room studio, that would be excellent, and you could even divide it in two, for a decent size control room and a small iso booth, if you needed to do that. 25 x 11 makes it rather long and narrow for a control room, proportionally: the ratio isn't going to work out so well, but the floor area is fine, and the ceiling height is fine.

I will primarily be recording rock bands in here. The drums are going to be the main concern. Is a 90 ft2 "tracking room" big enough for a real drum kit, or would it sound better in an overall bigger single room with well designed variable acoustics?

That's not such a simple question... Deciding on 1 room or 2, there's a lot of things to take into account. For example, many mix engineers want to hear the sound of each drum mic through the control room speakers while they are setting up the mics, and also when tracking. If the drums are in the CR, then that's kind of hard to do! Also, most mix engineers value their ears, and don't want to have their hearing messed up from very loud percussive acoustic sounds just a few feet away. So that's a couple of things to think about. On the other hand, tracking drums in a small room is never going to sound like Abbey Road Studio 1! Drums do like a lot of air around them to sound great. But if you plan to mostly close-mic the drum kit then add room ambience in the mix, that might not be too much of an issue.

You can physically fit a drum kit in 90ft2, yes, with mics (unless the kit is really large), so from that point of view, it's possible. The issue is the sound that you are looking for: if you want a natural big room sound, it isn't going to happen in 90f2! But then again, it isn't going to happen in 275 ft2 either. That would be a bit better, certainly, but to get a really good drum sound you need a lot of space. So it's just as much an issue of how you intend to record, as it is of physically fitting them in comfortably: close mic'ing in a smallish room can work well.

If the drums would be better in the single room scenario, should I still build some kind of booth for either vocals or guitar cabinets? (maybe just a smaller one?)

Some of the same reasoning applies here, as for the drums. Eg. loud amps in the CR are not good for your ears, and you would not be able to hear the mic sound in the CR speakers. Also, if you plan to track vocals along with a rock band, you probably want to have the vocal mic well isolated from the instruments. The vocalist will likely appreciate the quiet of the booth.

Everything I read says the rear wall behind the mix position is sacred ground. But that's exactly where the door would need to go to get into the booth or room if I build it. I would assume the door would be dead center because the rear corners would absolutely need heavy bass trapping?

Right. The rear wall is, indeed, the biggest problem in control rooms, always. But the door isn't too much of an issue, if it is in the middle of the wall. Its the sides and top of that rear wall that need the most attention. The middle is important too, but there are ways of dealing with that door. If that's the only wall it can go on, then that's fine.

The door to outside, if I do double doors, the exterior door will open outward and the hinges will be exposed on the outside. For normal construction, that's never supposed to happen. Do the hinges need to be stainless steel or something similar so they don't rust in the elements?

How about using sliding glass doors? They save space in the rooms, let in lots of natural light, etc. You can still have outward-opening doors if you prefer, and you could use any non-rusting hinge, such as brass, bronze, aluminium, stainless steel, etc. I'm assuming that you'll have some type of covering over the door area (roof extension, canopy, etc.) to keep the direct elements off the hinges. There are also recessed hinges that an be sunk into the edge of the door and the jamb, if it's a big concern for you.

How much does just the typical "stuff" in the control room affect the sound? For example, the electronic drum kit in the corner, the stack of small PA speakers in the other, the rack of guitars, assorted cases, amps, you get the idea. Should I try and plan for some kind of storage to remove those things from the room?

There's two ways the "stiff" can affect the room. First, just from the physical presence of the object, interfering with the sound path, and/or causing reflections to the mix position, etc. There's a general rule of thumb that an object only has a substantial effect on sounds whose wavelengths are small than the dimensions of the object, so small objects only reflect and interfere with highs frequencies, while larger ones affect mids too. The second issue, is the noise that the "stuff" might make, in response to the sounds in the room. For example, an acoustic guitar might decide to "sing along" with the music, due to sympathetic resonance, of the music happens to be playing a note that it can resonate at. Ditto acoustic drums: the kick, snare, and toms might "boom" along with the music, or there might be rattles, ringing and other vibrations from loose mechanical parts (the handle or latch on a road case). Those things might or might not be an issue, depending on how loud they are, but they could potentially be annoying or distracting as you try to mix: spending time trying to fix the strange booom in the mix, when it is really coming from the drums in the room, can be frustrating! (Been here, done that... ) Road cases and hard-shell instrument cases can also resonate.... So leaving an area for storage is a good idea. You do also need a place to store your spare mic stands, mics, cables, unused gear, etc.

I didn't see any dimensions but his small corner control room, built to help create the biggest live room possible in the space caught my eye. Do I have enough space for a design like that? Or will the control room be too small?

Possibly, but I'm not convinces. That corner control room measures 12'7" wide and long, by 9'7" high, roughly. It's more of a trapezoid than a square (which is why it works OK acoustically). I don't think you have enough space to pull that off, but you could try to fit that in with your design. When you are designing a studio, it's always a good idea to try out several alternative layouts, then see which one works best. With that studio, I think I went through 11 or 12 different layouts before settling on that one.

I'm really wanting to create something special here that I can actually use as a semi-professional recording studio. Am I being unrealistic with the space I have?

I don't think you are being unrealistic, no! It's a good sized space, there's a potential for good ceiling height too, you have the need to create a pro-level studio, you are doing the due diligence carefully, asking the right questions, taking the right decisions... so it seems to me that you are very much being realistic. You might want to increase your budget a bit if you need variable acoustics, very high isolation, or two rooms: that's probably the only part that could be more realistic. Building a studio always costs more than you imagined it would, when you first came up with the idea!

I just don't really know what the best design plan is, if you could point me down that road, I would be forever grateful.

I would start by writing down your goals for the studio: what it is you really want to accomplish. How you envision a typical tracking or mixing session. What instruments would be in there? What gear? Who would be sitting/standing where? Do you need to hear the instruments in the CR speakers without also hearing the actual instrument sound itself? Do loud sounds in the CR bother you? Etc. Just write down as much as you can think of about the studio, and how you want it to be: sometimes just the act of writing it will lead you to decisions.

Then figure out how much isolation you need, by using a hand-held sound level meter. That's important for the design of our isolation system.

Then do some preliminary rough sketches of possible layouts, using real dimensions for things like the drum kit, desk, chairs, people, instruments, speakers, etc, to see if you can get a workable layout that meets what you wrote down in the first step. Is it physically possible to have all those people, instruments, and gear in the studio if it is two rooms? And if it is one room? Etc.

Studio design is an iterative process: you juggle things around, compromising some things in order to improve others, based on your own priorities as well as on the principles of acoustics. It does take time! But it is well worth spending that time to get it right! Moving lines around on paper, or on the computer screen, costs nothing: Moving walls around after they have been built, is a bit more expensive. So spend the time to plan it right. And I'd suggest that you do it in SketchUp, rather than on paper: it's much easier to move things around, once you get the hang of the software.


- Stuart -

Stuart,
First of all, let me say that I really appreciate the time you take to answer all these questions. Your insight is invaluable. That being said, here goes round three of more questions.

First off have a look at these two basic layouts (in 2D). I'm starting to work with Sketchup, but it's a slow process, and I don't want to really get into it (in full 3D) until I'm more sure of my floor plan.

I have decided that I want to do 2 rooms, and have a small storage area. These are the two options I've come up with so far.


This design allows for 2 feet of bass traps in the rear corners of the control room. I think it makes the most of the available space, but it requires 7 doors! One pair to the house (north), one pair to outside (south), one pair into the drum booth (east), and one on the storage closet (that doesn't have to be solid, the closet will be inside the shell of the booth).

Here is design #2:


Now this one wastes a bit of the space, and makes the rooms dangerously close to squares (I can play with the dimensions some if this idea is even worthwhile). But this one, I believe, can be done with just 4 doors, and no double doors. The entire center becomes a sound lock/storage area. That's why it's 5'9" wide instead of just a 36" hallway, so there's room to put cases and equipment up against the wall.

You suggested sliding glass doors before, but it looks like acoustic rated sliding glass doors could run $3000 each! Two doors is almost a third of my budget, so I think those are out.

So what is your opinion of these two designs? Am I wrong in my thinking?

Also I have a few general questions that have come up as I've been researching.

The "inside out" room design, every inch of the walls and ceiling done that way has a frame on the outside for acoustic treatment. Isn't that going to make the room too dead? Or do you do different things in each panel as you go to avoid this?

The ceiling, seems to me it's going to be 3 leaf no matter what I do. There's the original roof in the attic, which does have a vented deck like you guessed before. Then there will be the new higher ceiling built on the outside walls, followed by the ceiling built on the inner walls. I've seen it said that sometimes it can't be avoided and that's ok. Just would like to know what I'm losing with this design.

Now a word about isolation. I measured with an SPL meter as best as I could. I'm just not 100% sure what it's telling me.
I cranked my speakers in my current bedroom studio until the meter read 110dB (C weight, slow response). Outside the window in the yard measured 75 dB, but the house is brick and the new construction will be vinyl siding, so that may be apples and oranges, but the new construction won't have a window, so that might even it up.

At 85 dB in the room it was 60 dB in the yard.
With everything off it was 55 dB in the room, turning off the central AC dropped it to 51 dB, all I could hear was the faint chirping of crickets in the yard. Going into an interior bathroom with no windows the reading dropped to 45dB.

Outside on the patio the ambient noise was at 60 dB, which was road noise in the distance and the crickets again. A car came down the street and the meter jumped to 70 dB.

So what does that tell me? Local law says max levels of 60 dB 8am to 10pm, and 55 dB between 10pm and 8am. That's also at an "A" weighting, which seemed to lower my readings by almost 15-20 dB when I tried it out. So it seems to me if the meter reads about 50-60 on the exterior of the house once everything is built, I should be good. So at normal mixing volume (85dB) I'm going to be pretty close to that with almost no extra isolation. But when I have a drummer bashing away at 115 dB or so, I'm going to need about 55 dB of reduction. So what does that equate to, construction wise? I looked at the gypsum wall thickness paper, and it showed a double wall system with two layers of sheetrock on either side to have and STC of 67. From what I understand that's just an arbitrary rating? That doesn't mean if I build the wall like that its going to reduce my sound by 67 dB right? How much isolation can I expect from that system?

The above paragraph also makes me consider the possibility of isolating the booth intensely, but not going so hard at the control room. Is that viable, or a bad idea?

Again, thank you so much for your time Stuart. I'm sure I'll have a whole new batch of questions by the time you answer this!

Scotty

First of all, let me say that I really appreciate the time you take to answer all these questions. Your insight is invaluable.

Thank you for the kind words. Feedback like that is always nice!

First off have a look at these two basic layouts (in 2D). I'm starting to work with Sketchup, but it's a slow process, and I don't want to really get into it (in full 3D) until I'm more sure of my floor plan.

A couple of very key points about SketchUp.

1) Don't try to use the free on-line browser-based monstrosity: it's a toy, and not a very good one. Rather, download the full (and also free) desktop version, here:

https://help.sketchup.com/en/downloading-older-versions

Get "SketchUp Make 2017". That's the one you want. It was the last free version that is fully featured.

2) When you are modelling your studio, each time you create a piece of geometry, immediately make it into a "component". In other words, make sure you have all the faces and edges of that "thing" selected, hit the "G" key, give it a name, and hit OK. There's many reasons for doing that, but the big one is this: it keeps all parts of the item together (eg, the six faces and 12 edges that make up a stud), and you can then create copies of that stud, that will all resize together if you change the size of any one of them. That's very useful!

3) Use the "layers" window to control the various parts of your model. In other words, put all of the studs on a layer called "studs", then combine that with other layers you make into one called "wall", then combine the four walls into yet another layer called "control room walls", then combine that with the layers where you have your ceiling, floor, doors, windows, furniture, etc. onto yet ANOTHER layer, called just "control room". When you build a hierarchy of layers like that, in nested levels, you have very powerful control over what you can see and not see. I find this VERY useful once the model starts getting complicated, as I can make some part invisible to be able to see other parts clearly, so I can work on them.

4) Use the "scenes" window to create a set of viewpoints for your model, along with the set of layers that you want visible (or invisible) for that viewpoint. That's how you can create an animated walk-through of your studio. Such as this one I did for a client in Australia a few years ago:

Also here, if the above doesn't work:

You can see how the various layers are turned on and off at different points in the walk-through, so you can see other parts that would be hidden otherwise. (By the way, the client just joined the forum a few days ago, and is planning to start a build thread about how he built that: The studio is completed and operational, so there's a lot he can show there, that will be useful for others)

So, by using components, layers, and scenes logically, you have a very powerful tool for designing and visualizing your studio.

I have decided that I want to do 2 rooms, and have a small storage area. These are the two options I've come up with so far.

I would go with the first option. The second one shrinks the rooms too much, and there's poor sight lines and access between rooms. In fact, your first option is a lot like the studio in the video above, except that you have the storage area on one side of the booth.

but it requires 7 doors!

And as you also mentioned, if you are building for moderate to high isolation, then each wall will consist of two leaves, and there will be one door in each leaf. You can see this in the video above. So, keep your doors to a minimum! Doors are expensive... and potential weak points for isolation too.

One pair to the house (north), one pair to outside (south), one pair into the drum booth (east), and one on the storage closet

Do you need doors on both sides of the live room? You probably do (one to outside, one to house), but its good to ask anyway. You might also need more than that, if for example you wanted a direct path into the drum booth, to avoid going through the CR.... Right now, your load-in / load-out path to the booth, is through the CR. So any time somebody wants to change the drum kit, the have to drag each part of it through the CR to get there... then drag it out again, after the session is over...

Also, with layout #1, I would flip it around so you are facing the drum booth, and replace the doors there with sliding glass doors, for good visibility, good access, and reasonable isolation.

You suggested sliding glass doors before, but it looks like acoustic rated sliding glass doors could run $3000 each! Two doors is almost a third of my budget, so I think those are out.

It depends on how much isolation you need: A pair of ordinary sliding glass patio doors can do a fairly decent job of isolation, if there's a decent sized air gap between them. Not as good as proper acoustic doors, of course, but if you can live with lower isolation between rooms, then that's a possibility. You can find that type of door at any good hardware store, and it won't cost you 3 grand! The thicker the glass, the better...

The "inside out" room design, every inch of the walls and ceiling done that way has a frame on the outside for acoustic treatment. Isn't that going to make the room too dead? Or do you do different things in each panel as you go to avoid this?

Yes, it does make it too dead... but that's the point!

Let me explain a bit:

There's two approaches to designing/treating a room. Actually, three, but the first one isn't on the cards for most home studio builders, so we'll just stick with these two:

1) Start with the room being very "bright", with highly reflective solid, massive, surfaces all around, then add absorption and maybe diffusion to get that under control.

2) Start with the room being mostly "dead" and lifeless, then liven it up with reflective and maybe diffusive surfaces.

Both approaches work. Personally, I prefer the second option, but the first one is valid too. I find it easier to start out with "dull", then add stuff to put some life back into the room. Often, that is with slats where you can vary the width and spacing to get the return that you want. Sometimes with poly-cylindrical diffusers, or maybe even numeric-sequence diffusers, if the room is large enough. The advantage of the "inside-out" wall here is that most of the absorption is hidden inside the walls, and the slats over it become the final finish surface of the walls. If you start out with a solid, hard wall, then your only option is to hang stuff on top of that to do the treatment. With "inside out", the treatment is integral to the wall. I prefer that, as I think it looks neater.

The ceiling, seems to me it's going to be 3 leaf no matter what I do. There's the original roof in the attic, which does have a vented deck like you guessed before. Then there will be the new higher ceiling built on the outside walls, followed by the ceiling built on the inner walls. I've seen it said that sometimes it can't be avoided and that's ok. Just would like to know what I'm losing with this design.

Right. In your case, you don't really have a choice. That's OK. As long as you are aware of that, and build accordingly, to get the isolation you need.

Now a word about isolation. I measured with an SPL meter as best as I could. I'm just not 100% sure what it's telling me.
I cranked my speakers in my current bedroom studio until the meter read 110dB (C weight, slow response). Outside the window in the yard measured 75 dB,

. So you are getting around 35 dB. That's a bit better than typical house walls.

At 85 dB in the room it was 60 dB in the yard.

That's strange: you reduced the level by 25 dB inside, and it only dropped by 15 dB outside? Hmmm... hard to explain that....

Local law says max levels of 60 dB 8am to 10pm, and 55 dB between 10pm and 8am.

Man, you are lucky! Those are unusually high limits for noise regulations! Often they have ludicrously low levels, such as 45 dB day and 35 dB night. So you are fortunate in that sense.

That's also at an "A" weighting, which seemed to lower my readings by almost 15-20 dB when I tried it out.

Right. Typical contemporary bass-heavy music will show up about 20 dB louder on C than on A. There's no way to convert between them, though, as it depends on the music itself. But since regulations are pretty much always "A" weighted, that's also in your favor.

So it seems to me if the meter reads about 50-60 on the exterior of the house once everything is built,

Sort of! But not really. In order to be inaudible, a sound needs to be quieter than ambient. So if your drums are getting out at 60 dB, and the ambient level is also 60 dB, then the drums will be audible. Muffled, but still audible. Depending on which school of thought you follow, to be truly inaudible the level should be 15 dB lower than ambient, or 20 dB lower... or maybe some other number. Under those conditions, you would want another 15 dB of isolation to ensure that your drums are completely inaudible.

However, having said that, there's also the advantage of distance: sound levels fall off with distance from the source, so if there's a long distance between your studio and your property line, you might find that its enough to get your levels down .

But when I have a drummer bashing away at 115 dB or so, I'm going to need about 55 dB of reduction.

55 is doable. As luck would have it, that's about what we are getting with the studio in the video above. I checked with the owner a couple of days ago, and he confirmed that he is getting around 55 dB of isolation. It's possible, and achievable.

I looked at the gypsum wall thickness paper, and it showed a double wall system with two layers of sheetrock on either side to have and STC of 67. From what I understand that's just an arbitrary rating? That doesn't mean if I build the wall like that its going to reduce my sound by 67 dB right? How much isolation can I expect from that system?

Right! STC is not the same as Transmission Loss in decibels. STC is actually a lousy way of measuring studio isolation: it's just an index number, not a true isolation number.

Here's something I wrote about that a while back:

STC is no use for telling you how well your studio will be isolated. STC was never meant to measure such things. Here's an excerpt from the actual ASTM test procedure (E413) that explains the use of STC.

“These single-number ratings correlate in a general way with subjective impressions of sound transmission for speech, radio, television and similar sources of noise in offices and buildings. This classification method is not appropriate for sound sources with spectra significantly different from those sources listed above. Such sources include machinery, industrial processes, bowling alleys, power transformers, musical instruments, many music systems and transportation noises such as motor vehicles, aircraft and trains. For these sources, accurate assessment of sound transmission requires a detailed analysis in frequency bands.”

It's a common misconception that you can use STC ratings to decide if a particular wall, window, door, or building material will be of any use in a studio. As you can see above, in the statement from the people who designed the STC rating system and the method for calculating it, STC is simply not applicable.

Here's how it works:

To determine the STC rating for a wall, door, window, or whatever, you start by measuring the actual transmission loss at 16 specific frequency bands between 125 Hz and 4kHz. You do not measure anything above or below that range, and you do not measure anything in between those 16 points. Just those 16 small bands, and nothing else. Then you plot those 16 points on a graph, and do some fudging and nudging with the numbers and the curve, until it fits in below one of the standard STC curves. Then you read off the number of that specific curve, and that number is your STC rating. That's it. There is no true relationship to real-world decibels: it is just the index number of the reference curve that is closest to your curve. To clarify: the STC number is NOT how much isolation you will get: it is just the number that somebody once assigned to a curve on a graph. So for the STC-70 curve, they could have called it "STC-GGFQRT" or "STC-Delta-RED" or "STC-Elephant-seven" or anything else, and it would tell you just as much about isolation as "STC-70" does: ie, nothing. It's a REFERENCE number, not an actual isolation number. For speech conditions, yes, STC-70 might actually be close to 70 dB of isolation, but not for music.

When you measure the isolation of a studio wall, you want to be sure that it is isolating ALL frequencies, across the entire spectrum from 20 Hz up to 20,000 Hz, not just 16 specific points that somebody chose 50 years ago, because he thought they were a good representation of human speech. STC does not take into account the bottom two and a half octaves of the musical spectrum (nothing below 125Hz), nor does it take into account the top two and a quarter octaves (nothing above 4k). Of the ten octaves that our hearing range covers, STC ignores five of them (or nearly five). So STC tells you nothing useful about how well a wall, door or window will work in a studio. The ONLY way to determine that, is by look at the Transmission Loss curve for it, or by estimating with a sound level meter set to "C" weighting (or even "Z"), and slow response, then measuring the levels on each side. That will give you a true indication of the number of decibels that the wall/door/window is blocking, across the full audible range.

Consider this: It is quite possible to have a door rated at STC-30 that does not provide even 20 decibels of actual isolation, and I can build you a wall rated at STC-20 that provides much better than 30 dB of isolation. There simply is no direct relationship between STC rating and the ability of a barrier to stop full-spectrum sound, such as music. STC was never designed for that, and cannot be used for that. It was meant for describing isolation of speech, not music. It's reasonably useful for what it was designed for, but not very useful for music.

Here's a graph that demonstrates this clearly:
That shows the actual TL graphs for two different walls. They have THE SAME STC RATING! I don't recall exactly, but they are both rated at STC-55 or something like that. But as you can see, the steel stud wall is far, far worse than the solid concrete wall in the low end, where it matter most. At 80 Hz, for example (often around the point where the kick drum is tuned, and certainly in the range where the bass is really pumping), the concrete wall is isolating at about 40 dB, while the steel stud wall is barely able to do 10 dB... In other words, the concrete wall is about 30 dB better at isolating, than the steel stud wall... but they are both rated the same STC... (Yes, the steel stud wall does hav an advantage in the mid range, from about 250 Hz to 2 kHz, and that's why it gets such a high STC rating: because that's the only part o the spectrum that STC considers! Outside of that, where STC doesn't even measure, the steel stud is far worse.)

Then there's the issue of installation. You can buy a door that really does provide 40 dB of isolation, but unless you install it correctly, it will not provide that level! If you install it in a wall that provides only 20 dB, then the total isolation of that "wall+door" combination is about 20 dB: isolation is only as good as the worst part. Even if you put a door rated at 90 dB in that wall, it would STILL only give you 20 dB. The total is only as good as the weakest part of the system.

So forget STC as a useful indicator, and just use the actual TL graphs to judge if a wall, door, window, floor, roof, or whatever will meet your needs.

---

The above paragraph also makes me consider the possibility of isolating the booth intensely, but not going so hard at the control room. Is that viable, or a bad idea?

That's a possibility, yes. As long as you promise to never turn up your speakers to "check the bass"! That's what engineers call it, when they feel like cranking it up to insane levels, to bask in the glory of the sonic monster they have created... If you can keep your levels down (which is a smart thing to do, to protect your hearing!), then yes, you can isolate the booth to a higher level than the control room.

Again, thank you so much for your time Stuart. I'm sure I'll have a whole new batch of questions by the time you answer this!

- Stuart -

Real quick, I think I got my design! Only question is how much space do I need at the front of the control room for soffits and speakers? Look at the drawing (my last in 2D, I promise!). Is that 2'2" I left in front of the door enough? And is the door to the house that can't be moved ok where it is? (Rectangle between CR & booth is sliding glass doors). FYI, I played around with the dimensions in the mode calculator (figured avg ceiling height at 9'), and neither room was too bad. I'm thinking with this setup, I won't need double doors anywhere except the sliders?

I did my first full 3D Sketchup model! Which points out a whole new batch of questions! So here we go.

First, the model itself: Both JPG & SKP



1. The gap between the stud frames of the inner and outer walls. In the model I have 1" between them all except at the front, because the garage door is going to need more because of the way it's built. Is that enough?

2. Should I put a bigger gap between the two double sliding doors between the CR and the booth? The sliding doors won't be the super acoustic ones per your earlier advice.

3. If I do the inner walls inside out, what should the gap be then?

4. The storage area at the entrance doesn't need the double wall construction, but leaves a weird gap in the wall I'm not sure what to do with. See the attached JPG.


I believe overlaying the drywall to cover the gap will couple it to the wall of the control room on one side and the exterior wall on the other. Also putting drywall on both sides of that wall makes a triple leaf now. Is that OK since the "air gap" is a full 3' wide closet? Doing it inside out solves the 3 leaf problem, but I still have the gap....

5. How much space do I need for the soffit mounted speakers in the front? Because of the door to the house, this design only gives me about 2 feet. I can either make the booth smaller, or put the desk facing away from the booth if that's not enough space.

6. I have several options for the ceiling, with the potential for each room different.
The storage room ceiling will just be 8' tall flat.(Because why make a closet complicated?)

The booth can be done either about 10' high flat, peaked, gabled, or in a right triangle.

The control can be done either peaked, gabled, or in a right triangle.(to do it flat would make the ceiling only about 8 feet high.)

My inclination is the do the control booth gabled for symmetry, and do the right triangle on the booth, so the lowest point would be about 10' and the highest would be about 14'? Thoughts?

PS: As I'm writing this and thinking about it, I may need to do the double wall construction in the closet anyway to get rid of the strange gap and to make the ceiling construction remain isolated. I can still probably get away with just single doors....?

Thanks as always,
Scotty

Great! That's an excellent start on your 3D SketchUp design.

1. The gap between the stud frames of the inner and outer walls. In the model I have 1" between them all except at the front, because the garage door is going to need more because of the way it's built. Is that enough?

Probably, yes. What type of sheathing did you have in mind for your walls? In other words: Are you planning in just one layer of drywall on the studs, or maybe two layers, or maybe a layer of OSB plus a layer of drywall?

This goes back to the issue of how much isolation you need, and the frequencies you need it at. The more mass you have on each leaf, the more isolation you get. And the bigger the gap between the leaves, the more isolation you get. I have a spreadsheet that I've developed for estimating isolation, but it's far from being ready for public consumption. However, if you let me know what your plans are for sheathing, then I can plug that into the spreadsheet and see what it says. (There are a couple of other spreadsheets out there on the internet that claim to do the same, but beware of some of those! the answers they give don't math reality very well! Nor do they match things like IR-761 or other documents. There's some good spreadsheets and calculators out there, but also some really lousy ones. I'm trying to perfect mine to be more accurate, and one day I'll release it, but not yet: it still needs work to clean it up.)

2. Should I put a bigger gap between the two double sliding doors between the CR and the booth? The sliding doors won't be the super acoustic ones per your earlier advice.

It would help, yes. Bigger air gaps are always better. But here too it would be worthwhile estimating how much isolation you need, to see how close you can get, and if it is worth increasing the gap.

One technique that can help here is to install the doors themselves to be even further apart than the leaves of the walls: In other words, have the doors "sticking out" from the wall a little, so the air gap is larger between the glass panes than it is between the actual sheathing. If you do decide to go "iniside-out" on those walls, then its very easy to do that.

3. If I do the inner walls inside out, what should the gap be then?

How much isolation are you aiming for? Ideally, the cavity depth between the two leaves should be at least 4" (10cm) for most cases, and more is better: Studs are already 3.5" deep, so for example if you leave a 2.5" gap up to the inner-leaf frame, then put on sheathing that totals 1.25", that would leave a cavity of 4.75", which should be fine. (I'm assuming that the outer-leaf wall will be done conventionally, with the studs facing the cavity).

4. The storage area at the entrance doesn't need the double wall construction, but leaves a weird gap in the wall I'm not sure what to do with. See the attached JPG.

Assuming you need high isolation for that drum booth, I would do it something like this:
You do lose a little space like that, but here too you could do that inside-out if you wanted. Another option might be to do the wall to the drum booth with Resilient Channel, which would save you space and also save the need for an extra door there, at the cost of not-quite-so-good isolation.

5. How much space do I need for the soffit mounted speakers in the front? Because of the door to the house, this design only gives me about 2 feet. I can either make the booth smaller, or put the desk facing away from the booth if that's not enough space.

I did a few quick layouts to check, and yes, you just barely have enough space to do soffits... assuming that you are not using large speakers. I checked with both the Adam A7X and the KH120, and it is possible to do soffits in that space with both of them. But if you wanted something like a KH420, or even a Focal Trio, that would not fit. As long as your speakers are not too deep, then yes, you have enough space... Just! If you could move the dividing wall just a little, you could maybe fit in a larger speaker.

Have you decided on speakers yet? The size of the speaker defines how deep your soffit will be...

6. I have several options for the ceiling, with the potential for each room different.
The storage room ceiling will just be 8' tall flat.(Because why make a closet complicated?)

The booth can be done either about 10' high flat, peaked, gabled, or in a right triangle.

Whatever gives you the greatest air volume inside the room, and the highest overall peak height. Drums like air around them, and especially above them, to sound their best.

The control can be done either peaked, gabled, or in a right triangle.(to do it flat would make the ceiling only about 8 feet high.)

For the CR, there's two "rules" to take into account:

1) Symmetry is critical for the front half of the room, so whatever you do to the ceiling, it should be symmetrical at least from the front wall as far back as the mix position. Behind that, it's not so critical, but still good if you can do it.

2) The room should not get lower at the back, if possible. It's fine to have it lower at the front, sloping up, but not so fine to have it sloping the other way.

So keep those in mind when you are deciding how to do your ceiling. Apart from those two, make it as high as you possibly can, and also allow for deep treatment up there.

My inclination is the do the control booth gabled for symmetry, and do the right triangle on the booth, so the lowest point would be about 10' and the highest would be about 14'? Thoughts?

Sounds good in theory! Maybe do a rough simulation in your SketchUp model, to see how it looks in practice.

It's good to see things progressing with your design!


- Stuart -

What type of sheathing did you have in mind for your walls?

If I do normal construction, there will be 1 layer of OSB and a second layer of 5/8" fire rated drywall with green glue between them. I like your idea of not having to search for a stud to hang things.
If I do inside out construction, it will just be 2 layers of 5/8 fire rated drywall with GG.
I'm guessing the OSB should be 5/8 as well?

Have you decided on speakers yet? The size of the speaker defines how deep your soffit will be...

I have a pair of the original Event 20/20 BAS from about 2002. Dimensions are approx. 10"W x 12"D x 14.5"H. I know them very well but they are pretty old. If budget allows at the end of the build I may upgrade them to either the Focal Solo6 or the HEDD Type 20, depending on $ left. How much space would I need for the Hedd? It's not much bigger than the events but its oriented differently. 14"W x 13"D x 11"H. That being said, I'm probably going to inch the wall back anyway to give me about 3' in front of the door.

I think the Focal Trio or the Hedd Type 30 are too big for my space.....

While we're on the subject of monitors, what's your feeling about subs? I was always under the impression they were for hype and had no place in a critical listening environment. That being said, today's Hip Hop & EDM seems to actually have a need to monitor those sub frequencies. I don't typically mix those types of music, but I'd be willing to give it a shot if a client came along.....

Assuming you need high isolation for that drum booth, I would do it something like this:

Sometime you become so intent on solving a problem, that the simple solution just escapes you. Once I saw your drawing it was obvious. Perfect solution!

2) The room should not get lower at the back, if possible. It's fine to have it lower at the front, sloping up, but not so fine to have it sloping the other way.

At the rear of the room the ceiling will slope back down (from flat) somewhat due to the hip roof construction. However that slope should only be about 2' at most and that's probably about how deep the bass traps will be at the back, so it shouldn't be a big deal right? See SKP & JPG below for how the main roof of the house sits over the garage:




OR.... should I flip the control room around to face away from the sliding glass door? I was thinking about it and if we did it that way the roof could probably start low, but get even higher as it heads to the booth. Also, if I were tracking a live band: drums in the booth, guitar and bass direct in the CR and vocal in the CR, they could all be much closer to each other rather than looking over me and the desk to the drummer in the booth. Also would make running the cables from the desk to the booth cleaner as they wouldn't have to pass on the ground in some kind of track where people will be walking to go in and out of the booth. Only issue I see is a 5' glass wall dead center of the rear mixing room wall. Thoughts?

Now for the random questions/thoughts of the day.

1. Inside out walls, just to confirm my suspicions, there is no need to tape and mud the drywall if it is going to be installed interior, correct? Just acoustic caulk the seams and make sure the 2 layers are staggered?

2. The insulation in the wall cavities, pink fluffy is fine? Rockwool and/or OC 703 are used for the treatments? Or would it be better with Rockwool or OC 703 in the walls as well? Is there a reason to use one over the other or are they interchangeable? (OC seems to be much more expensive.)

3. Back to inside out walls. It worries me some that all the walls will end up being fabric. I see guitar headstocks catching and ripping it, musicians leaning guitars against it, or leaning themselves right through it! What has been your experienece with the durability? Also, look at the below picture of inside out construction.

The 75mm insulation needs to be Rockwool or OC 703 for treatment. Does the 50mm insulation between the walls also need to be? Or again, is pink fluffy ok there? And does there need to be a space so that it doesn't touch the exterior wall studs or insulation? Do you even need that 50mm insulation if the outside wall it's facing is already a single leaf insulated stud wall and not external block like shown?

4. I assume it would be ok to mix and match the inside out and standard construction methods? I'm thinking the back wall and front wall of the control room would be standard, since they're going to get thick bass traps in the rear and speaker soffits in the front, the side walls of the CR and all 4 walls of the booth as inside out, the closet as standard, and the ceiling standard, as all the angles in the ceiling are going to make inside out difficult. Again, thoughts?

5. The bass traps in the rear, most everything I see says 2 feet thick, is that correct? Should I allow for more if I have the room? Is that just the corners or the entire wall?

6. Speaking of cables above, the electrical cables and the audio cables will be running through the attic and dropping down the walls. What's the usual method? Drill holes through the top plate to drop down the cable? Then caulk it? Or should I try to drop them between the inner and outer walls?

7. Looking ahead to HVAC. Confirm this for me, mini splits and/or central AC do not provide fresh air. A ventilation system of some sort to remove and replace the air (6 times per hour I think it was?) will be required for airtight construction. A through the wall unit (if I wanted to make the closet an exchange chamber) would provide fresh air, but it would need to be running all the time? Not very efficient I would think.

I think that's all I have for now. Thanks again Stuart! I'm really getting excited that it's taking shape!

PS: I met with a contractor who came up with the idea to build a fake garage door out of wood. From the front it will look just like a garage door but the interior will be a solid wall, which buys me back 5" or so in the front! Which I can shift to the space for speaker soffits! And the contractor plays bass in a local band, so although he's never built a studio, he gets the importance of doing it just right!

Scotty

If I do normal construction, there will be 1 layer of OSB and a second layer of 5/8" fire rated drywall with green glue between them. I like your idea of not having to search for a stud to hang things.
If I do inside out construction, it will just be 2 layers of 5/8 fire rated drywall with GG.

It's a good idea to do the OSB in any case: it provides sheer strength for the wall, which drywall doesn't do very well.

I'm guessing the OSB should be 5/8 as well?

Right. The thicker it is, the more mass it has, and that's good for isolation.

I have a pair of the original Event 20/20 BAS from about 2002. Dimensions are approx. 10"W x 12"D x 14.5"H. I know them very well but they are pretty old. If budget allows at the end of the build I may upgrade them to either the Focal Solo6 or the HEDD Type 20, depending on $ left. How much space would I need for the Hedd? It's not much bigger than the events but its oriented differently. 14"W x 13"D x 11"H. That being said, I'm probably going to inch the wall back anyway to give me about 3' in front of the door.

Once you decide on the speakers, let me know and I'll plug the dimensions into a tool I created to help in designing soffits. It shows how things will work out for any specific size of speaker, along with a few other dimensions.

While we're on the subject of monitors, what's your feeling about subs?

I love 'em! OK, maybe "love" is a bit strong, but I do often use subs in studios. The reasons for that are:

1) If the mains don't go down very low, and need some help.
2) Using subs meas you can do a better job of isolating the mains, since the mains won't be putting out very low frequencies.
3) Subs can help a lot with some modal issues, as well as SBIR and a few other things.

I was always under the impression they were for hype and had no place in a critical listening environment.

It depends on how well they are integrated. If the mains already go down low, and the room is very well treated for the low end, then subs might not be needed. But they can improve things a lot, if they are installed right.

The decision should be based mainly on what your speakers are capable of, what your music needs, and what your room needs. Your Event 20/20s go down to about 35 Hz, which is pretty good, so with those you might not need subs to cover the spectrum well... but you might still benefit from theme for other reasons.

For example, in a room that still has low-end modal issues even after treatment, I use a pair of subs set up as a "plan wave bass array" (sometimes also called a "double bass array"). That's a special setup where the subs work together with the room to kill modal issues, or at least greatly reduce them. You need two subs to do that, and a careful process to place them correctly and tune them correctly, but the results can be very good. You can also use a sub (or two) to deal with SBIR. So it's not just for show or hype: they can be very useful, if done right.

Sometime you become so intent on solving a problem, that the simple solution just escapes you. Once I saw your drawing it was obvious. Perfect solution!

At the rear of the room the ceiling will slope back down (from flat) somewhat due to the hip roof construction. However that slope should only be about 2' at most and that's probably about how deep the bass traps will be at the back, so it shouldn't be a big deal right? See SKP & JPG below for how the main roof of the house sits over the garage:

Hmmm.... you might be able to get away with that, but it's going to need some tricky treatment up there, to keep it all under control.

OR.... should I flip the control room around to face away from the sliding glass door? I was thinking about it and if we did it that way the roof could probably start low, but get even higher as it heads to the booth.

You could do that, but then you end up with a reflective rear end in your room. The big glass doors to the booth... That's would really complicate things...

Also, if I were tracking a live band: drums in the booth, guitar and bass direct in the CR and vocal in the CR, they could all be much closer to each other rather than looking over me and the desk to the drummer in the booth.

There's a lot of glass in those doors: should be enough room for everyone to see each other, even if you are in the way. Assuming you have a low-profile desk, that would improve visibility even more.

Also would make running the cables from the desk to the booth cleaner as they wouldn't have to pass on the ground in some kind of track where people will be walking to go in and out of the booth.

The cables to the booth should be done through the walls, not on the floor. The simplest method is to just put in an ordinary snake, with the stage box attached to the wall in the booth and the other end hard-wired into your desk, to the console, DAW, patchbay, etc. The cable itself runs through the walls, and ideally through the floor too.

Ditto for the CR itself, if you plan to do a lot of tracking in there. Run a snake to the rear of the room, with the stage box on the side wall, and the cable itself hidden in the wall, running to the desk. Keep the floor clear of cables as much as possible.

Only issue I see is a 5' glass wall dead center of the rear mixing room wall.

Yup! That is, indeed, a big issue!

1. Inside out walls, just to confirm my suspicions, there is no need to tape and mud the drywall if it is going to be installed interior, correct? Just acoustic caulk the seams and make sure the 2 layers are staggered?

Correct. You could mud and tape if you wanted to, but there's no need. Staggered joints and good caulking will do the job just fine.

2. The insulation in the wall cavities, pink fluffy is fine? Rockwool and/or OC 703 are used for the treatments? Or would it be better with Rockwool or OC 703 in the walls as well? Is there a reason to use one over the other or are they interchangeable? (OC seems to be much more expensive.)

They type of insulation doesn't really matter that much, acoustically: either fiberglass or mineral wool will do the job. What matters is the rather obscure parameter called "gas flow resistivity", or GFR, which is measured in the even more obsucure units of MKS rayls!. That's a measure of acoustic impedance, actually, and describes how the material reacts to sound. But you don't need to worry too much about what that all means (unless you really want to know). The problem is that manufactures of insulation don't usually even bother to measure that, as it has no meaning for the main use of their product: thermal insulation. It only matters to us crazy folks who want to build recording studios using their insulation! Fortunately, there are "rules of thumb" for estimating GFR for different types of insulation, using the density of the insulation. So you'll often see recommendations to use "3 PCF mineral wool", for some acoustic device, or maybe "20 kg/m3 fiberglass" for another device.

OK, you can actually ignore most of the above! It's just a brief explanation to help you understand the issue a bit. Basically, you can use either mineral wool or fiberglass in your walls. If mineral wool, then something with a density of around 50 kg/m3 is fine, which is about 3 pcf (Pounds per Cubic Foot). If fiberglass, then go with something around 30 kg/m3, which is roughly 2 pcf. Anything in that ball park will do the job.

One other issue here: mineral wool stands up to water a lot better than fiberglass insulation does. If fiberglass gets wet, it gets soggy, sags, and crumples a bit. If mineral wool gets wet, nothing happens except that it is wet! . Fiberglass does not recover when it dries out: it stays in its saggy, crumpled state. Mineral wool dries out, and is fine. So if your insulation might get wet while you are building, then go with mineral wool. It is also more fire resistant that fiberglass.

Now, when it comes time to treat your room acoustically, then you'll need to be more discerning: density, GFR, and type of insulation can be more important when designing treatment.

3. Back to inside out walls. It worries me some that all the walls will end up being fabric. I see guitar headstocks catching and ripping it, musicians leaning guitars against it, or leaning themselves right through it! What has been your experienece with the durability?

Simple! Never allow a musician with an instrument in your room!

Ok, on a more serious note: I use tough fabric, such as the type that is used to make upholstery, couches, chairs, etc. Or speaker grill cloth. That stuff can take a beating, and not get damaged. I also try to lay out the room so that people don't need to be close to vulnerable areas, and I use wood slats, trim, or other things to protect some places where damaged is very likely, such as directly behind the couch, or close to doorways.

In fact, with an inside-out wall, there's usually not much surface left that is just plain fabric after the room is fully treated. Considering that surrounding your entire room with thick insulation makes it pretty dead acoustically, there's a need to put a lot of reflective surfaces around the room to bring it back to life. Careful placement of such surfaces not only tunes the room acoustically, but also protects the fabric.

Also, look at the below picture of inside out construction.

That's a pretty old picture, from way back. It's done a bit different today. Acoustics has advanced a lot since that image was made, and acousticians today use more modern techniques. For sure, the floor would not be done that way! That's very old-school, and would not work well, for many reasons.

The 75mm insulation needs to be Rockwool or OC 703 for treatment.

It could also be other things, depending on what you needed to do acoustically. Completely filling he cavity of a Helmholtz resonator like that can be counterproductive: it can over-damp the very resonance that you need in order to make it work! So you might or might not need 75mm of insulation, and it might or might not need to be 703, or one of the Rockwool products. Rockwool is a brand name, and they make many different products, with different characteristics and purposes. So if someone tells you to "use Rockwool for that", then first ask them. "Which one?"!

Does the 50mm insulation between the walls also need to be? Or again, is pink fluffy ok there?

As above: If you use mineral wool (Rockwool products are mostly mineral wool), then something with a density or around 50 kg/m3 (3 pcf) would be fine, and if you use fiberglass, then 30 kg/m3 (2 pcf) would be fine. If you use another type of insulation, such as polyester, or cotton, or wool, or denim, or cellulose, then the density would need to be different in each case, since each TYPE of insulation has different GFR properties.

And does there need to be a space so that it doesn't touch the exterior wall studs or insulation?

No. There should never be a gap. That's one of the things that is wrong with that image. The entire cavity should be filled with insulation, and it can (and should) touch both surfaces. It can be compressed just a little if you have to, but it's better to not compress it. So if you have 6" of depth in your cavity, then use 6" thickness of insulation.

There are several reasons for this "rule", but the two big ones are that the insulation slows down the speed of sound (or more correctly: the speed of sound in insulation is lower than it is in air), so the cavity seems to be deeper than it really is, to the sound waves. They "feel" like they are traveling a longer distance than the actual depth of the cavity, which is good. The second reason is that the insulation changes the way the air deals with heat, from "adiabatic" to "isothermal". I won't go into the technical details, but basically "isothermal" is more efficient at removing sound energy. So, filling the cavity completely means that all of the cavity slows down the sound wave, and all of the cavity removes energy more efficiently. If you leave an air gap, you are wasting that space! Even worse, the air gap itself can, under some circumstances, resonate, and that would rob you of isolation. So the diagram is wrong. That's the way things were done 40 or 50 years ago, before these things were widely understood well. But today, there is better understanding, and there are are better methods that are more effective.

Do you even need that 50mm insulation if the outside wall it's facing is already a single leaf insulated stud wall and not external block like shown?

Yes, you always need the insulation in the cavity. It acts as an acoustic damper on all the resonances that would otherwise occur in there. It's a major part of the isolation system. Very necessary.

4. I assume it would be ok to mix and match the inside out and standard construction methods?

Yep! No problem.

I'm thinking the back wall and front wall of the control room would be standard, since they're going to get thick bass traps in the rear and speaker soffits in the front,

I would still do the front and back inside-out, as it gives you extra space. For example, at the front you get more space inside the soffit, so you could have a larger speaker....

the side walls of the CR and all 4 walls of the booth as inside out, the closet as standard,

and the ceiling standard,

You can gain a lot of height by doing the ceilings inside out... Take a look here: http://www.digistar.cl/Forum/viewtopic.php?f=12&t=50

as all the angles in the ceiling are going to make inside out difficult.

It should be possible to adapt the inside-out technique to an angled ceiling. I haven't done that (yet!), but I think it it is feasible. It would just be a bit harder to raise the modules.

5. The bass traps in the rear, most everything I see says 2 feet thick, is that correct? Should I allow for more if I have the room? Is that just the corners or the entire wall?

Two feet is bare minimum! I often use three feet in the corners, or more, and two feet in the middle. A "standard" Superchunk corner trap runs three feet down the side wall and three feet across the rear wall, for example. So definitely, if you have more space then use it. The deeper the better. The defining characteristic is the lowest axial mode f the room: you need to make your bass traps deep enough to damp that effectively. So figure out what the wavelength of the lowest mode will be, multiply that by 0.07, and that's the minimum thickness you should consider for your rear corner bass traps: For example, if you figure out that your lowest mode is going to be 35 Hz, the wavelength for that is 32 feet, times 0.07 = 2.24 feet. So 27 inches, minimum.

6. Speaking of cables above, the electrical cables and the audio cables will be running through the attic and dropping down the walls. What's the usual method? Drill holes through the top plate to drop down the cable? Then caulk it? Or should I try to drop them between the inner and outer walls?

Here's how I usually do wall penetrations for cables:









Use PVC conduit Bend it to an "S" shape with gentle curves, with the ends far apart, so the holes in the two leaves do not line up. For high isolation cut out an inch or so in the center, and wrap it with rubber. Hold in place with tie-wraps, and seal with duct tape. Pull the cables through, then plug both ends with insulation poked down deep into the conduit, and seal with a generous blob of caulk.

7. Looking ahead to HVAC. Confirm this for me, mini splits and/or central AC do not provide fresh air.

Right! The vast majority of minis-splits do no, by themselves, provide any ventilation air. I'm only ware of two models that do provide a small mount of air, but way, way short of what a studio needs.

A ventilation system of some sort to remove and replace the air (6 times per hour I think it was?) will be required for airtight construction.

Right! Sort of.... This gets to be a bit complex. You need to circulate the entire volume of air in your room six times per hour (once every ten minutes), to ensure good cooling, good mixing, etc. And you ALSO need to bring enough enough fresh air to provide the oxygen that you need to stay alive, while ALSO removing the same amount of stale air, full of CO2 that you exhaled, and other nasty stuff. But you DON'T need to replace all of the air six times per hour! You only need to smaller amount of fresh air/stale air ventilation, not all of it. I mean, you CAN do all of it if you want, but that's not efficient. It costs you money to cool or heat the outside the air that is coming into the room, and if you ten dump that air out again ten minutes later... that means you dumped all the money you spent heating or cooling it! hmm... not very efficient! It would be better to keep conditioned air around for as long as possible, until it really needs to go. It turns out that, for most climates, you only need to replace about 20% to 30% for the room air with each cycle.

So there's TWO things going on: one is that you are circulating a lot of air through the room, and the other is that you are taking out some of that and replacing it with fresh air.

For a typical room, the re-circulation rate might be 200 CFM (Cubic Feet per Minute), but you might only need 50 CFM of fresh air. So the HVAC system for that room would need to do both: circulate 200 CFM around the room AND ALSO bleed off 50 CFM to dump overboard, and replace that with 50 CFM of fresh air.

It's actually a bit more complex than most people realize. It takes a bit of math to figure out, and some attention to detail in the planning.

If you want to see how it is done, then we are doing that right now on Tom's thread: http://www.digistar.cl/Forum/viewtopic.php?f=6&t=32 He's at the stage right now where w are discussing his HVAC system, so you might want to follow along, and pick up some tips on how to do the same thing in your place.

A through the wall unit (if I wanted to make the closet an exchange chamber) would provide fresh air, but it would need to be running all the time? Not very efficient I would think.

Right! I'm not a big fan of the "exchange chamber" concept, and even less of a fan of through-the-wall systems. They are noisy, and inefficient! Use only the "mini-split" type of system, along with a ventilation system. In Tom's case, we are going to do it with a ducted mini-split system, that combines both concepts into one single system. It is also possible to use a ductless mini-split system, which only does the circulation, and a separate ventilation system, to provide fresh air an remove stale air. Both ways are valid, both work. I prefer ducted, as it is more effective and more efficient.

I think that's all I have for now. Thanks again Stuart! I'm really getting excited that it's taking shape!

PS: I met with a contractor who came up with the idea to build a fake garage door out of wood. From the front it will look just like a garage door but the interior will be a solid wall, which buys me back 5" or so in the front! Which I can shift to the space for speaker soffits! And the contractor plays bass in a local band, so although he's never built a studio, he gets the importance of doing it just right!

Cool! If he can pull that off, with good mass and seals, making it look like an ordinary garage door, that would be great! 5" extra room length would be very useful.

- Stuart -

"The more I know, the less I understand."
-Don Henley-

**WARNING** This post is a little all over the place....

Now that I have somewhat got my basic design concept, I've been reading everything I can about HVAC. I still have plenty of reading and research to do on it, but just a few generic questions to point me in the right direction...

For simplicity's sake, let's ignore the booth and the closet and imagine we're dealing with just the control room.

1. Ducted mini split - AHU will be up in attic, conditioned air duct will run to properly sized silencer box then to register into room, typically at the rear. The return air register will be at the front of the room (typically), attached to it's own silencer box, and run back to the AHU, with a smaller duct branching off right before the AHU to outside for fresh air intake. The small fresh air duct may need an inline fan to provide the correct amount of fresh air.

2. Ductless mini split - The return air would pipe directly to outside, and the fresh air would pipe separately from outside. The fresh air register would be directly above the wall mount unit. And a fan would only be needed on one of the duct runs, either return or fresh. You would still need the silencer boxes at each register.

Is this basically correct? If so there are some specific questions that I didn't see a clear answer for.

a. Flexible duct is fine for runs of 5' or less, anything more must be steel, either round or rectangle?
b. The silencer boxes, MDF or OSB? A couple of the threads I read went back and forth, possibly a mistake they didn't even realize, but the two are different materials!
c. If the silencer box penetrates 2 leaves, you need a separate box for each leaf? Or you must cut the outgoing vent and join it loosely with neoprene and mastic?
d. What holds the silencer boxes in place? You can't just screw to to the studs can you? Do they need to be decoupled from the stud bays they are in with rubber or something?
e. The movie of the studio you sent me that's similar to mine looks like there are silencer boxes on the outgoing and incoming air vents. Why are those necessary if the termination is outside of the isolated leaves? That corner everything is in seems like it's isolated from the booth (like my closet).
f. Is the passive ventilation system good enough? Or should I be looking at an ERV? New Orleans has pretty mild winters and pretty long brutal summers with oppressive humidity. The temperature chart below understates the weather, because of the humidity it feels like over 100 degrees for most of the summer.


I know there is plenty math for figuring out the exact sizes of everything and I will research that next, for the moment I just want some general clarity.

My last thought on AC for the moment: My booth is barely 80 ft2 and the closet is 30 ft2. Most of the heat and activity will be in the control room most of the time. If all three rooms are on the same system, then when the control room is comfortable both those rooms will either be freezing or overheated due to their size and construction. I'm thinking I can condition those two spaces from my main house AC unit, adding an extra 110 ft2 shouldn't be an issue. That should keep them at a decent temperature independent of the control room. Of course I will add return vents to them. I'm thinking the fresh should be ok since the house return is standard, leaky construction?

Now a few more questions from the previous post:

The cables to the booth should be done through the walls, not on the floor.

I understand that, what I was asking is what to do with the cable coming from the wall to the desk. Same question will apply to speaker cables from the soffit mounted speakers. See crude pic below. (Blue rectangle is stage box, arrow is pointing at cable on the floor).

I use tough fabric, such as the type that is used to make upholstery, couches, chairs, etc. Or speaker grill cloth.

So not the Guilford's of Maine that everyone seems to use? Is the Guilford's tough enough? Do you have a link to an example? I know the material must be breathable.

So figure out what the wavelength of the lowest mode will be, multiply that by 0.07, and that's the minimum thickness you should consider for your rear corner bass traps: For example, if you figure out that your lowest mode is going to be 35 Hz, the wavelength for that is 32 feet, times 0.07 = 2.24 feet. So 27 inches, minimum.

I had also asked you about subwoofers. I was thinking of just building the room and possibly adding a subwoofer later, but from reading this, if I stay with my current speakers that go to 35Hz, my bass traps need to be 27" minimum. If I add a sub and go down to 20Hz, the bass trap needs to be 48" minimum! I guess I need to decide on a sub here and now then, before I have to deconstruct the back wall and add bass trapping?

And finally, I keep coming back to my strange shaped roof. Let me post some pictures and ask some more questions. Please excuse these pics as they are VERY crude...

Below is a house with standard roof beams, joists, and walls, all wood in brown.

The original recommendation is to remove the ceiling joists, put in collar ties higher up, and that will allow the inner leaf ceiling to gain some more height. See below:(Of course none of this is even close to scale)


The original roof is vented in from the soffits and there is a 12" x 12" attic fan that vents out. There is no ridge vent. My questions are:

1. Are you supposed to sheetrock the outer leaf? You could put rock and insulation on the collar tie part, and I guess you could put rock on the angled part, but you couldn't do insulation on the angle because air needs to be able to rise from the soffits up the roof. Or are you supposed to add another roof beam at a smaller angle like below?

If the above is correct, then now you do have room for sheetrock and insulation without interfering with the venting of the attic. BUT, if my inner leaf ceiling is going to be inside out, this outer ceiling will have the rock and insulation on the wrong side, and there would be no way to put it on the attic side due to corner space constraints. Should it just be left unsheathed?

Finally, I am having a structural engineer come out to make sure, but two different contractors have taken a look and told me that the way my roof is supported over the whole house, the joists across the garage can be removed and do not need to be replaced with collar ties at all. If so, I could end up like this:

What would the isolation be like this? The outer leaf would not be airtight because of the soffit vents, the vent fan, and just general normal house construction. Would this totally sabotage all the isolation I was trying to achieve?

I hope this makes sense. Thanks for the help as always!

Scotty

"The more I know, the less I understand."

A great summary of the quest for learning acoustics! That should be the motto for all first-time studio builders...

1. Ducted mini split - AHU will be up in attic,

You could put the AHU in the attic, yes, or you could also put it in the ceiling area of the storage room. I'm not certain, but there might be enough space for it there, and it would be easier to access for cleaning, maintenance and repairs.

conditioned air duct will run to properly sized silencer box then to register into room, typically at the rear. The return air register will be at the front of the room (typically), attached to it's own silencer box, and run back to the AHU, with a smaller duct branching off right before the AHU to outside for fresh air intake. The small fresh air duct may need an inline fan to provide the correct amount of fresh air.

Sounds about right, yes.

2. Ductless mini split - The return air would pipe directly to outside, and the fresh air would pipe separately from outside. The fresh air register would be directly above the wall mount unit. And a fan would only be needed on one of the duct runs, either return or fresh. You would still need the silencer boxes at each register.

Correct. I recommend the ducted option as the best choice, but in some cases ductless is the only option, for various reasons. It's less effective, but it does still do the job.

a. Flexible duct is fine for runs of 5' or less, anything more must be steel, either round or rectangle?

You can go longer with flex duct if you want to, as long as it is fully extended and well supported, with no kinks or sharp turns. For long runs, it's usually a good idea to go one size larger (diameter) if possible, to reduce velocity, improve static pressure, etc.

b. The silencer boxes, MDF or OSB? A couple of the threads I read went back and forth, possibly a mistake they didn't even realize, but the two are different materials!

Either is fine. MDF has the weight advantage, for sure: OSB is around 620 kg/m2, MDF is around 750 kg/m3. So MDF is about 20% more dense. OSB is lower, but still better than plywood or drywall. OSB usually has the price advantage: it's cheaper. OSB also resists moisture better (unless you immerse it in water). The choice usually depends on how much isolation you need, and some other factors. But MDF, OSB and plywood are all options, with various pros and cons.

c. If the silencer box penetrates 2 leaves, you need a separate box for each leaf? Or you must cut the outgoing vent and join it loosely with neoprene and mastic?

For moderate to high isolation, I go with separate boxes per leaf. For low to medium isolation, you can sometimes get away with a single sleeve that goes through both leaves, but is decoupled in the middle, as you mentioned. I would use rubber, though (EPDM, neoprene, Sorbothane, etc.): not just mastic. Mastic isn't flexible enough to get good decoupling.

d. What holds the silencer boxes in place? You can't just screw to to the studs can you? Do they need to be decoupled from the stud bays they are in with rubber or something?

For high isolation, I suspend them from hangers, with rubber under them. This is often just something simple like angle-iron hung from threaded bar, with suitable nuts and washers:

e. The movie of the studio you sent me that's similar to mine looks like there are silencer boxes on the outgoing and incoming air vents. Why are those necessary if the termination is outside of the isolated leaves? That corner everything is in seems like it's isolated from the booth (like my closet).

Right. That's a high-isolation project: the owner of that studio teaches drums, so he sometimes has two drum kits going at once. Hence, the need for high isolation. Also, there was very little space there for the HVAC system, since he built that under his house. So there are floor joists up there. In order to save as much room height as possible, I put some of the silencers in the bays between joists up there, and others in that "closet" area, linked with flex duct. The AHU in this case is ductless, as there just wasn't any room to get a ducted unit in and still have it serviceable.

f. Is the passive ventilation system good enough? Or should I be looking at an ERV? New Orleans has pretty mild winters and pretty long brutal summers with oppressive humidity. The temperature chart below understates the weather, because of the humidity it feels like over 100 degrees for most of the summer.

I would check with your local HVAC suppliers, but an HRV or ERV might be a good option in your case, with the hot humid climate in summer (I do remember my trips to New Orleans! Hot and humid, for sure!). But it's not really a passive system, if you have an AHU in there. The AHU is still doing a lot of cooling, and also dehumidifying. What an HRV will do in addition, is take some of the load of the AHU, which means lower energy costs. An HRV transfers some of the heat in the incoming air to the outgoing air: in other words, it cools the incoming air by transferring the heat to the outgoing air, which means that you don't lose the "cold" in the outgoing air, that you paid a lot of money to cool down. An ERV does that, but it also transfers humidity from one air stream to the other. So an ERV can gain you some extra efficiency, since once again the AHU then does not need to remove that humidity from the incoming air. It might be worthwhile in your case to install an ERV, but they don't come for free! You still have to spend money to buy one, so you should get the HVAC people to do a cost/benefit analysis, to show you how fast you will recover the cost of the unit in the money you save from not having the AHU running at full capacity all the time. They should be able to show you that, put into local terms for New Orleans. It's certainly worth looking at, but an ERV does not replace the AHU: you still need the AHU, either ducted or ductless.

My last thought on AC for the moment: My booth is barely 80 ft2 and the closet is 30 ft2. Most of the heat and activity will be in the control room most of the time. If all three rooms are on the same system, then when the control room is comfortable both those rooms will either be freezing or overheated due to their size and construction.

Not if you do it right! If the system is dimensioned correctly, then both rooms should be similar. You could go fancy and have a "zoned" system, of you wanted to too, where each room has its own thermostat which controls a damper to proved less flow or more flow as needed. But that's probably not necessary.

I'm thinking I can condition those two spaces from my main house AC unit, adding an extra 110 ft2 shouldn't be an issue.

Perhaps! But find out from your local HVAC people if the system has the extra capacity to deal with that space. There's several things to take into account: Air flow rate, air flow velocity, latent heat, sensible heat, and static pressure, among other things. Studios are different from other rooms, in that the flow rate must be high while the flow velocity must be low. That doesn't matter for a living room or bedroom, but its critical for a studio: you do not want to hear the noise of air moving in a studio. So check with whoever provided your current home system, to make sure you have enough excess capacity to do that, without overloading it.

I understand that, what I was asking is what to do with the cable coming from the wall to the desk.

Ahh! OK, got it! Best place for those is in the floor, if possible. Otherwise they can go in a "tunnel" on top of the floor. I'm not sure if you are following Tom's amazing build, but we just went through that process a couple of days ago: viewtopic.php?f=6&t=32&start=49 Take a look there. In the end, he embedded all of his in the floor slab as it was poured, but since your floor is already poured, that's probably not an option! I would suggest going with the "chase a wide groove in the floor" option that I showed there. It's not that hard to do. Messy and dusty, though!

So not the Guilford's of Maine that everyone seems to use? Is the Guilford's tough enough? Do you have a link to an example? I know the material must be breathable.

Guilford of Maine is good stuff... and pretty tough, too. It's good quality, and doesn't puncture or rip easily.

I had also asked you about subwoofers. I was thinking of just building the room and possibly adding a subwoofer later, but from reading this, if I stay with my current speakers that go to 35Hz, my bass traps need to be 27" minimum. If I add a sub and go down to 20Hz, the bass trap needs to be 48" minimum! I guess I need to decide on a sub here and now then, before I have to deconstruct the back wall and add bass trapping?

It's possible to do bass traps in other ways, that are thinner... and it's no really necessary to trap everything down to 20 Hz. You only need to trap the actual modal issues that you have, and you won't have anything down that low. Your lowest mode (lengthwise axial) is going to be around 35Hz, based on your current CR dimensions, so you won't need to treat 20Hz as there won't be any modes that low. That will be in the pressure region, not the modal region, so it can't really be treated that way... There might still be some issues down there, from structural or pressure zone issues, but not really treatable easily, and not really necessary to treat anyway. The six string bass goes down to around 31Hz (open B0 is 30.9Hz, to be precise), and that's the lowest instrument you'd normally be dealing with. The only things that go lower than that are the cathedral pipe organ, and the concert grand piano. Probably not instruments you'll be tracking or mixing regularly in your place! I'm not sure if you have seen the Studio 3 Productions thread: viewtopic.php?f=8&t=14 You can see that there's still some minor stuff going on around 28 Hz, but it's not an issue at all in the room. There's no need to be worried about stuff way down there, where no instrument ever goes.

In general, bass traps only need to cover down to about 30 Hz, regardless of how low the subs can go. So why do you need a sub that goes even lower? Clarity. That's one of the issues. A speaker that, on paper, goes down to 35 Hz is really getting close to its limits when playing music in that region: it's working really hard to do that. But a sub that goes down to 20 Hz (for example) isn't even breaking a sweat at at 35 Hz. So it can produce the note more cleanly. It can also move a lot more air while doing that, because it probably has at least a 10" cone, and likely larger. So it can really shove around a whole bunch of air, to fill the room nicely, while an 8" cone is struggling to do that. Let the mains do what they do best: mids and highs, plus the upper end of the lows, and let the sub do what it does best: moving lots of air in the very low end. There's also the advantage of having the sub(s) in a different location physically from the mains, so it can deal with some of the acoustic issues left behind by the mains from their locations.

The original recommendation is to remove the ceiling joists, put in collar ties higher up, and that will allow the inner leaf ceiling to gain some more height. ... The original roof is vented in from the soffits and there is a 12" x 12" attic fan that vents out. There is no ridge vent.

1. Are you supposed to sheetrock the outer leaf? You could put rock and insulation on the collar tie part, and I guess you could put rock on the angled part, but you couldn't do insulation on the angle because air needs to be able to rise from the soffits up the roof.

I would call that the "middle leaf", not the outer leaf: the roof itself is your outer leaf. You are adding another leaf between that and the final inner-leaf ceiling, so technically it should be the "middle leaf". There's a method for dealing with the insulation in the angled part: you create ventilation paths through it, using roof deck ventilation baffles, like this:









Those things hold back the insulation, creating a ventilation path under the roof deck.

BUT, if my inner leaf ceiling is going to be inside out, this outer ceiling will have the rock and insulation on the wrong side, and there would be no way to put it on the attic side due to corner space constraints. Should it just be left unsheathed?

You need the insulation in both places: no top of the "middle leaf" deck (in other words, inside the actual attic space), and also in between the middle-leaf and the inner leaf. Plus, you usually also want insulation on the ceiling inside the room, for acoustic treatment reasons. All of this is independent of how you build the inner-leaf ceiling: if it is inside-out or conventional makes no difference here: you still need insulation in all three locations, for different reasons.

Finally, I am having a structural engineer come out to make sure, but two different contractors have taken a look and told me that the way my roof is supported over the whole house, the joists across the garage can be removed and do not need to be replaced with collar ties at all. If so, I could end up like this:

That would be nice! But do make sure you get a signed, written report from the structural engineer, saying that it has his blessing to do that. Make sure he understands that you plan to take out the entire ceiling, including all of the joists. I'm not convinced he'll sign off on that!

But even if he does sign off on that, your third sketch is not going to work, as you would then not have a sealed outer-leaf: the ventilation path under the roof deck prevents that.

They way isolation works is that you have two leaves with air trapped between them. It's called an "MSM" system, meaning "Mass - Spring - Mass", because the air acts as a spring. The inner-leaf sheathing is one one "Mass", the outer-leaf sheathing (or middle-leaf sheathing in your case) is the other "Mass", and the air trapped between them is the "Spring". This is a tuned resonant system. It resonates at one specific frequency, given by the amount of mass on each leaf, and the "resilience" of the air spring between them. The system is tuned so that the resonant frequency is at least one octave lower than the lowest frequency you need to isolate. Done like that, you get excellent isolation. But both leaves have to be sealed air-tight for that to work properly. If one of them is not sealed, then there's no air spring, so it doesn't work. If there are holes in one of the leaves, then the sound simply leaks out through the holes! So both leaves must be air tight... but the eave vents prevent that... which is why you need a middle-leaf ceiling in your case (and all other cases where the roof deck must be ventilated). The sheathing on that middle-leaf is sealed air-tight, so the MSM system is restored, and you get isolation.

What would the isolation be like this? The outer leaf would not be airtight because of the soffit vents, the vent fan, and just general normal house construction. Would this totally sabotage all the isolation I was trying to achieve?

Short answer? Yes it would sabotage your isolation.

The best way to think of how isolation works is this: if there's a gap where air can get through, then sound can get through too, because sound is just vibrations in the air. Even a tiny gap in one leaf can have a major effect on trashing your isolation. Here's a graph that shows how much isolation you lose from having a very small hole in your wall:


Sorry that it's not very clear! But you can see the issue. The top curve on that is for the case where you have a gap that is 0.01% of the area of the wall. So if you had a wall that is ten feet long by 8 feet high, the area would be 80 square feet or 11,500 square inches, and a hole of 0.01% would be 1.15 square inches. That would be like having a small crack just 1/16" wide and 18" long under part of the wall. The top curve on that graphs shows that, with this situation (1/16" crack, 18 inches long on a ten foot wall), if the wall was designed for 50 dB isolation, you would only get about 36 dB of isolation! And going down to the third curve, which is for 0.05% opening, if your gap were a bit bigger, at 1/8" and about 4 feet long, then your isolation would be 32 dB, instead of 50. At 1% open area, your 50 dB isolation is totally trashed, down to 20 dB.

It's a shocker to see how much you lose from even very small gaps... Now imagine the total area of all your eave vents, as compared to the area of the ceiling....

So the middle-leaf is something you really do need!


- Stuart -