Soundman2020 - Studio Design Forum

Ok, not soffit... Extended baffle?



You may be thinking, "Why on earth would you try to do that?"

1. I'm renting. Can't build into structure.
2. On second floor. Trying to keep weight down and there is a U-turn in stairwell, limiting size.
3. My best mixes were mostly done in rooms with soffit mount speakers.
4. The holes in the bottom are for air flow, a woofer on one side, computer and I/O on the other.

First, my goals, then my not entirely well educated ideas on the baffle.

I am a career mixing guy. More than 3 decades doing live and studio stuff. I want a mix room where I can produce professional results in a reasonable amount of time. My clients are hip to revisions adding to their schedule but sonically, fidelity-wise, I need to come out of the gate on target. Moved out of my professionally designed studio 12 years ago. (Still mixing live daily up until the pandemic. I can't imagine what we're going to need to do to get 2400 people back into a theater again.) I have some projects I'd like to get involved with so...

My wife has given me the master bedroom to play with. Biggest room in the house that is surrounded by (almost) 4 walls. All other rooms in the house have features like closets on one side, windows on another, L shaped... In this room I am facing a solid wall to the north exterior. West wall has a sliding glass door to exterior. East wall has the entry door to the room in the south corner, a bathroom is on the other side. South wall has a door sized opening into the connected bathroom - not quite in the center of the room.

13' 6.5" 162.5" 4127.5mm
12' 7" 151" 3835.4mm
7' 11.5" 95.5" 2425.7mm

That large cabinet in the drawing is just there to illustrate what happens at the edge of the baffle. When I drew that I had the idea in my head to do slant, sealed, slat boxes. I don't think I know enough to start to imagine how to build those in a helpful manner. Also, too big to get around the stair corner. I am redrawing plans at this point.

By making everything modular I will be able to move stuff around to experiment and take it with me when I move. My thinking is to build two or four 11.5" deep, 3' tall by 4' wide sealed boxes with 9" of stuffing upon which I can put; A) slats spaced strategically dependent upon tuning needs, and B) on top of each I can stack two 4' 11" tall by 2' wide, 9.5" deep not sealed absorbers. I will build four or eight more 2'x8'x9.5" deep absorbers. All of which, along with the extended baffle will give me almost complete floor to ceiling wall coverage. 9" of Safe N Sound in each frame, open sides and back. Add a cloud and three 24" superchunk and that's my starting point. Because the floor is carpet I anticipate adding slats in 1D diffusor patterns in the back to bring back in at least a little liveliness, but I'm not sure how or where yet. I don't have as much depth to the room as I would like. My listening position is 8' 3" from the back wall.

Anyway, more on that as I move along. For now I just want to know if I should included the extended baffle in my design or scrap it altogether. I have fear that I have missed some glaringly obvious result that my level of experience in acoustical modeling (none) has failed to anticipate. Refraction or some such...

Oh, I do have Everest and Gervais and some other books. It's been a while. But I can reference those at any time.

Thanks for any tips,

Mark J

Greetings Mark J,

While I will defer to the far-more experienced builders here, I do notice one thing in your design which might cause an issue: how will you keep the legs/struts/supports firmly on the floor? If you don't (and maybe even if you do), there will surely be an issue with vibrations entering the temporary structure once you introduce sound. This is important not just from a musical standpoint, but also a safety one: you don't want the thing collapsing due to the vibrations.

All the best,

Paul

Hi there Mark, and Welcome to the forum!

Congrats on deciding to make a good mixing room, that tells the truth! Soffit mounting is, indeed, one of the best things you can do to achieve that goal.

1. I'm renting. Can't build into structure.
2. On second floor. Trying to keep weight down

What is your floor made from? If it is a concrete slab, then you can probably put a fair amount of weight on it. If it is a light-weight wood "joist-and-deck" floor, then maybe not so much. But it should be possible to build a reasonably light soffit. The only thing that needs to be heavy, is the front baffle. The rest needs to be strong and rigid, but steel framing could accomplish that, or lighter weight wood species. Or even something more exotic, such as aluminium framing. The important thing is to determine just how much extra load your floor can handle. On other hand, a large fancy cast-iron and noble wood double bed, with a couple of large chunky hefty wood night stands, a large wood headboard, chest of drawers, wardrobe, sofa, etc. can add up to a lot of weight: typically what a master bedroom might be loaded with. It should be possible to make a soffit around the same total weight, and spread the load over a large area of floor... while still keeping it "removable": not permanently attached.

3. My best mixes were mostly done in rooms with soffit mount speakers.

Yup! For sure! There's a reason why they are so highly recommended, and so widely used in pro studios....

4. The holes in the bottom are for air flow, a woofer on one side, computer and I/O on the other.

Not a problem! That can be incorporated.... but it's a good idea to also incorporate acoustic treatment for the room. Room corners are key points for treatment: soffits go in corners....

13' 6.5" 162.5" 4127.5mm
12' 7" 151" 3835.4mm
7' 11.5" 95.5" 2425.7mm

A reasonable size. Still a "small" room, acoustically, so it will still need lots of treatment, but certainly usable.

By making everything modular I will be able to move stuff around to experiment and take it with me when I move.

Modular is fine, and a good idea for sure if you might have to move one day... but experimenting is not so necessary. Rather, use the science of acoustics to predict things, then design the soffits accordingly, and locate everything in the room correctly, according to theory... then test the outcome with REW, and modify as appropriate. That's a very brief summary of the process, of course, but that's the general idea. Test the empty room with REW, uses acoustic principles to design the treatment, then test again, and tweak.

OK; about your soffits: the basic concept is reasonable, but the implementation needs some work! One of the underlying concepts of soffits is that the front baffle has to be massive and rigid (not optional), and the original thinking was that the framing also has to be fairly rigid, so that the speaker vibrations don't get into the structure (as Paul mentioned: that is important!)... however, there are ways around that! It is also possible to fully decouple the speaker itself from the soffit, such that it "floats" inside it, and therefore does not transmit any vibrations into the structure. That's the way I do it with my soffit design, that I use in most studios these days. The "old school" approach was to make a hugely massive, very heavy, very rigid structure, and tightly jam the speaker into another very rigid, very massive "enclosure box", that is rigidly mounted to the frame and baffle, making one huge enormous monolithic "chunk" of mass. That's the way it used to be done, and some studio designers are still stuck with that concept in their heads: but I don't agree that this is the best way of doing things any more: especially if you have weight restrictions! Modern techniques and materials make that unnecessary. So I developed the "floating speaker" method, as an alternative, based on some original ideas from Barefoot. It's a little more complicated to do it my way, since there's some math involved to make sure that the speaker really DOES float inside the soffit, but to my way of thinking, it's a better outcome... lighter too!

And about "modular": I would suggest making your soffits out of a series of "stacked" vertical modules, each of which is small enough to fit down your stairs. However, you say this is a master bedroom, so I'd assume that it is possible to maneuver an entire double-bed up those stairs! Or at the very least, a double-bed mattress. That would be the limit on what size a module can be. But with the concept I have in mind, the modules could be rather smaller than a double-bed. I would suggest three modules: a "base" module, just up to the height of the speaker, then a "mid" module, that actually holds the speaker and floating mount assembly, then a "top" module with acoustic treatment. Each one would be maybe 28"-36" high, give or take several inches. They would just stack on top of each other, and be held together with bolts, internally.

That would be my suggestion.

The same applies to the soffit "wings", out on the side walls, which are actually an important part of the soffit: they aren't really sort-of optional add-ons that would be nice to have: rather, they are an integral part of how the soffit works, acoustically. And they could be modular too, and stackable in the same way: designed to fit together with the main part, and to be bolted to it in the same way.

Oh, I do have Everest and Gervais and some other books. It's been a while. But I can reference those at any time.

Those are both GREAT books, and highly recommended (on our "recommended reading list"... : viewtopic.php?f=9&t=15)... however, neither of them goes into much abut soffits. In fact, I'm not aware of any book that does! It seems to be a sort of "secret art"... which is why I'm working on an article about that! But it's a long way from being ready. One day, sometime, I'll post that...

But in reality, it isn't that difficult to build good soffits: what matter is getting the design right, ensuring from the outset that it will do the job right: by design, not by luck!

Anyway, that's my suggestion for your soffits.

Add a cloud and three 24" superchunk and that's my starting point.

Make the cloud "hard backed", and angled.

Because the floor is carpet

That's not so good for a studio! For psycho-acoustic reasons, the general rule for control rooms is "hard floor, soft ceiling". At the very least, the floor area between you and the speakers should be hard and reflective, never carpet. That's another key to good control-room acoustics. You are renting, so obviously you can't take out the carpet... but you CAN cover it! I would suggest that you just lay down a couple of sheets of MDF, plywood or OSB on top of th carpet at the front of the room, up to the mix position, and sit your soffits, wings and desk on top of that. (That would also help to spread the weight of the soffits over a much wider area, reducing the point load.) The rear of the room isn't so critical, so you could still leave that as carpet if you have to. If you don't like the look of bare OSB, then lay something like laminated flooring on top of it. It can look really good, and all of that is removable and re-usable, if you move.

I anticipate adding slats in 1D diffusor patterns in the back

Your room is not long enough to be able to do that, unfortunately. Most types of numeric-sequence diffusors create very uneven, problematic patterns in the region close to them, so that's a bad place to have your ears. Theory says that this uneven area of "lobing" extends out to about ten feet from the face of the diffuser, before it has smoothed over and is even enough to not b a problem. That "ten foot" distance is the minimum: it can be greater, if the diffuser is tuned low enough. It might be a lite less for some diffuser designs, but ten feet is a useful rule-of-thumb. So your room is not a candidate for numeric-sequence diffusers.

Instead, I'd suggest either poly-cylindrical diffusers, or carefully placed slats, to keep the high end in the room and provide the ITDG termination. Also, cover the actual insulation in your superchunks with plastic, for the same reason: not sucking up too much of the high end.

It sounds like you have the right basic idea, and a room that can be reasonably good (especially with soffits!). It's just a matter of putting together a solid acoustic plan.


- Stuart -

Thank you for the warm and surprisingly quick welcome.

@ Paul - Good point. I was noodling to some extent, but also not thinking enough about acoustics.

@ Stuart - The site looks good. Been lurking for a couple of weeks or so. I've always been a fan and I really appreciate your efforts and contribution. Also, I found your site just in time, I don't know what I would do without SketchUp. I haven't wasted a single piece of lumber since I started using it. I had been using Free because I didn't know about Make2017 or their dastardly Photobucketish plans.

It sounds like you have the right basic idea, and a room that can be reasonably good (especially with soffits!). It's just a matter of putting together a solid acoustic plan.

Right there is the elephant in my room. I've been in many studios that work. (And some that don't.) I know what a good room looks and acts like, but not entirely why. I have no practical experience in design and very, very little in construction. The more I read, the more I realize that practical experience is the only way to learn about this and the farther I get from starting due to uncertainty. That's why I posted here.

I've been thinking about this room for a couple of months. And have more ideas than I included in the first post. I just want to get started and knew I need to get the soffit answer out of the way first. I have started on and am half way done with the cloud because I knew no matter what, that and at least one superchunk would be necessary.

I have done baseline measurements with REW to your specifications but do not want to post the mdat here to reduce confusion because the speakers are at 90 degrees due to my desk needing to be rebuilt to get my video monitors out of the way. I want to redo the baseline with speakers, desk and vidmons in as approximate to final locations as I can. Probably a week before the desk is rebuilt. I know I don't like very wide speaker angles from experience and I think the soffit drawing is 70 or so degrees which is a known preference for me.

What is your floor made from?

Joist and deck. And it's "American Affordable" from the early 2000s. In one of the other rooms I can feel the floor move when my 40 pound dog comes in. Unfortunate, I know, but nothing downstairs is workable. For the baffle I was thinking 5/8" particleboard-green glue-3/4" finish plywood. The speakers are in boxes already. It was an arduous task fitting them exactly and getting them out will not be easy in any way. I have exactly 1 1/2" depth of baffle to play with. I have never used green glue and don't know how much thickness it will cure to.

Not a problem! That can be incorporated.... but it's a good idea to also incorporate acoustic treatment for the room. Room corners are key points for treatment: soffits go in corners....

Is it critical that the soffits go in the corner? I have 2 concerns. 1) I like to use delay a lot to create stereo trickery in my 2 channel mixes. I can judge what I'm doing better with a narrower splay and have to go to mono checks less often. 2) Where I'm sitting can't change much. While I don't know if I will be mixing in 5.1, I like to listen in 5.1. (Steven Wilson is knocking my socks off!) I intend to play around at some point and had intended to cross the front wall damping bridge when I got to it. I had hoped to put the LR speakers at about 70 degrees on a 48" radius and put superchunk in the corners behind the soffit. (Like the drawing in my first post.)

OK; about your soffits: the basic concept is reasonable,

I know that 5/8"+3/4" will be rigid, but will it be massive enough? My idea was to put the speakers on stands behind the soffit. Mains are 55.7lbs and 55.4lbs, and center is 22.4lbs. I have a stock of 1" Sorbothane and a calculator. I figured if the speaker is (actually) decoupled from the stand then it wouldn't matter if the stand was coupled to the floor/soffit? That being said, a multitude of different support ideas are running through my head right now. I am certainly interested in your floating method.



The queen box spring was stupid hard to get up the stairs. The mattress easier because it bends. We don't use a bed frame so didn't have to hassle that. This house was designed horribly. I'm not even going to start.. but the rent is excellent and our landlord the best. I like the base, mid, and top module idea. Can they be frame? Or do they need to be cabinet assemblies?

Also, when you say wings are you speaking of bits beyond what I was calling the "extended baffle" in the drawings? I was thinking that I would need to use the area to the sides of my position for absorption, or... does the soffit deal with that in another manner. (The guy who designed my studio had no absorption in front of about 3 feet behind my mix position. It was all very rigid. It worked well. But some people mentioned it was an outdated design.)

Modular is fine, and a good idea for sure if you might have to move one day... but experimenting is not so necessary. Rather, use the science of acoustics to predict things, then design the soffits accordingly, and locate everything in the room correctly, according to theory... then test the outcome with REW, and modify as appropriate. That's a very brief summary of the process, of course, but that's the general idea. Test the empty room with REW, uses acoustic principles to design the treatment, then test again, and tweak.

This is specifically where I don't have any solid ideas in my head. General principles are probably half understood and when I embark on the process I find huge gaps in my ability to imagine solutions. I'll lay out quickly where I am.

Depending on how well I'm interpreting REW the modal region is surprisingly even in frequency response with the only worrying dip at 2-1-1. However, sustain is off the charts in the first two octaves and bass response to the ear is anemic. It is not tracking the signal in any useful manner. Trying to interpret the ETC with string has lead me to believe that the first BIG reflection is coming off the front wall. I'm interpreting times that correspond to the side walls but can't seem to find the influence of the ceiling which I can't imagine has so little influence. This indicates to me that I have more learning to do. (Once again I do not want to upload the mdat unless the new "final" speaker position is very much worse and there is position noodling to do.)

So, my process was:
* Design soffit and place speakers. Baseline room.
* Build corners, cloud, and desk. Measure.
* Build soffit. Measure.
* At this point I'm really getting lost, but I had intended to use the side walls (wings?) to absorb early reflections at ear level and introduce early reflections at floor level -built deep enough for more bass trapping with the bottoms sealed in attempt to use slat spacing to do some additive narrower modal absorption. Measure.
* Continue to build floor to ceiling traps all the way around. Install slats on lower sides. Measure.
* Try to figure out how to align decay times and introduce liveliness that I suspect will get lost with so much bass trapping. Measure.
* Repeat.

Given where we are in the current discussion my plan is starting to look like throwing a bunch of materials at the space whilst neglecting the "plan" part of the deal.

Those are both GREAT books, and highly recommended...

I certainly want to get everything on that list and almost bought Kleiner and Tichy, and Cox and D'Antonio(<- cost = 25 yards of fabric), but realized if I did I would put back the start of this project 6 months at minimum while I tried to digest and incorporate the ideas. And the real truth of the matter is, I learn much better in practice. Once I have experience the more sense the reference material makes. Plus, my math skills are nil. But... I'm an old mix guy on a low budget. I find acoustics fascinating and beautiful but it's not my first concern here. If I had ample funds you'd be on your way to my new property at your next calendar opening.

:thu: Make the cloud "hard backed", and angled.

Ooh, another thing I overlooked concentrating on the wrong aspect. I have a huge dip at what seems to be caused by 2-1-1 centered at what seems to be 0-0-2. So I was trying to get the absorption down below 140. That gave me two air gaps, one in the trap and one between it and the ceiling. Am I correct in thinking that the hardback and slant will redirect residual energy to the rear of the room? Do I want it less absorbent? I currently have 703 and SnS at my disposal. Also, it seems like I would need a pretty steep angle? The frame top and bottom are done, depth has yet to be set. (Was 9") I haven't weighed it yet, but without stuffing it's ridiculously light.

I would suggest that you just lay down a couple of sheets of MDF, plywood or OSB on top of th carpet at the front of the room, up to the mix position, and sit your soffits, wings and desk on top of that.

Cool. I can fidget something like that. My desk is unruly and I don't know that lowering it will be easy, but I can certainly surround it with wood. The desk is weird, problematic, has nothing to do with mixing and you will learn more when I photograph it and post those picture here. For now I'll just say that it's footprint is dictated by my number one hobby.

Your room is not long enough to be able to do that, unfortunately. Most types of numeric-sequence diffusors create very uneven, problematic patterns in the region close to them, so that's a bad place to have your ears. ... Instead, I'd suggest either poly-cylindrical diffusers, or carefully placed slats, to keep the high end in the room and provide the ITDG termination. Also, cover the actual insulation in your superchunks with plastic, for the same reason: not sucking up too much of the high end.

Good info. I knew there were limits and that my room is too small for diffusion, just not the details. Polys are certainly doable. What I had in mind falls into the slats category. I thought I'd break up the spacing by copying a diffusor. Would a depth of 5/8" or 1/2" over an absorber actually difuse? Specular control seems very complex to me.



Thanks again for your attention to the subject and contribution to the world. Sound is too cool to not enjoy at it's best.

The more I read, the more I realize that practical experience is the only way to learn about this and the farther I get from starting due to uncertainty.

Getting into the theory a bit also helps! Not necessarily the math (although that can be very revealing too), but rather basic concepts.

I have started on and am half way done with the cloud because I knew no matter what, that and at least one superchunk would be necessary.

Right! Several superchunks in fact: it's a small room, and as you already noticed, the bass isn't behaving very well. Taming problematic bass needs a lot of treatment. Especially if you plan to use only porous absorption for the bass.

I have done baseline measurements with REW to your specifications but do not want to post the mdat here to reduce confusion because the speakers are at 90 degrees due to my desk needing to be rebuilt to get my video monitors out of the way.

The low end probably won't change a lot from the speaker angles. The mids and highs certainly will, but the low measurements depend mostly on the mix position and the room itself: to a smaller extent on the location of the speaker. What will change most from different speaker positions is the amplitude of the modes and other resonances, but the relationship between frequencies won't be hugely different, and neither will the decay slopes. Those are room-related, mostly.

One other point about your speaker angles: you might find this useful! : Speaker setup, and the equilateral triangle

Joist and deck. And it's "American Affordable" from the early 2000s. In one of the other rooms I can feel the floor move when my 40 pound dog comes in.

Hmmm... not so good. Quick question: do the walls in your room coincide with the walls in the room below? Asked another way: are your walls directly above the walls of the downstairs room? If so, they they might be load-bearing walls, which can help to a certain extent. But your best bet would be to get a structural engineer in there to take a look, and tell you what your loading can be.

For the baffle I was thinking 5/8" particleboard-green glue-3/4" finish plywood.

That would probably work: it's a bit on the light side, but should be OK. Question: You are going to use two mains plus a sub most of the time, correct? In other words, the mains won't be producing the low end, but rather the sub will be handling that?

Is it critical that the soffits go in the corner?

I probably didn't state that too clearly: The speakers will be located in the optimum position for the speakers, and the soffit front baffle will be located around the speakers, as well as possible. That won't be in the corner, but the rest of the soffit structure will be. Even though the speaker-and-baffle won't be covering the corner, there's a lot more inside the soffit that will be! I tend to speak of "the soffit" as being the entire thing: the part that contains the speakers, and the part above and below that, and the part outboard of that, which does go into the room corner, and is what I call the "wing". To my way of thinking, that entire thing is all "The Soffit", since all of the parts are working together to tame the room. Each part doing its own specific thing, of course, but then the combination of all of them doing "The Treatment", as well as holding up the speaker in the right location. The "Soffit" is doing many things at the same time, if it is properly designed.

I know that 5/8"+3/4" will be rigid, but will it be massive enough?

As I mentioned above, its on the low side, but probably in the ball park. However, it's not just the mass by itself: you also need rigidity. In other words, you don't want the baffle flexing and vibrating: it should be immobile across the entire face. Your support system doesn't seem to accomplish that: it only provides support at a couple of spots on the baffle, leaving the rest of it free to "shake, rattle, and roll"...

My idea was to put the speakers on stands behind the soffit. Mains are 55.7lbs and 55.4lbs, and center is 22.4lbs. I have a stock of 1" Sorbothane and a calculator. I figured if the speaker is (actually) decoupled from the stand then it wouldn't matter if the stand was coupled to the floor/soffit?

Here's the reason why I don't do it like that: If you have a speaker sitting on top of a stand, and then you have a fairly hefty voice coil on the woofer whapping around inside the box, thudding back and forth, while the cone is pushing a lot of air around as it moves... well, that can apply more than just a bit of force to the speaker in the front-back direction: it wants to "wobble" And since it is just sitting on a stand, there's nothing to prevent it from doing so! There is nothing to restrain that front-back movement. Which is not a good thing at all, as it messes up the highs as well... think of it this way: if the tweeter is producing frequencies up around the top end, say 17 kHz, then the wavelength is about 20mm (roughly 3/4"). The quarter wave is 5mm. If your woofer is able to move the entire speaker box even slightly, say just 2mm each way back-and-forth (less than 1/8")... well, you can see where this is going! At the furthest point in the "rocking chair" cycle, the tweeter is a quarter wavelength out of phase with where it would be at the other end of the cycle! That's 90°... one hell of a lot, in fact. When you consider that speaker manufacturers knock their heads against walls and spend millions of dollars on research to prevent the cone surfaces from "breaking up" into harmonic resonances of just fractions of a millimeter, it becomes clear that allowing a speaker to rock, wobble, shake, and dance about is a Big Deal. Hence, the need for rigidity in the soffit framing, and the soffit baffle.

Thus, I prefer to mount the speaker with resilient supports on all sides, not just underneath. In fact, very little of the total motion of a speaker is up-and-down! If you rest it in Sorbothane pads, then that's mostly what you are isolating: up-and-down motion... which isn't normally too much of an issue. Most of the motion is front-back, but there can also be side-to-side motion, and certainly vibration. So I prefer to hold the speaker in place in all three dimensions, but resiliently, such that it truly does float.

This is also part of the reason that those silly foam pads for resting speaker on, sold under various brand names, are actually quiet ineffective. Ethan Winer did a series of tests on several of those a few years back, and found that they basically achieve nothing.

I like the base, mid, and top module idea. Can they be frame? Or do they need to be cabinet assemblies?

Probably! But if you use framing, then it would have to be floor-to-ceiling... sort of the size of a double bed frame...

Also, when you say wings are you speaking of bits beyond what I was calling the "extended baffle" in the drawings? I was thinking that I would need to use the area to the sides of my position for absorption, or... does the soffit deal with that in another manner.

The basic function of a soffit is to remove the speaker from the room which eliminates or greatly reduces many of the artifacts associated with having a speaker inside the room. Edge diffraction, front wall SBIR, power imbalance, etc. They are gone, because they can only happen when a speaker does NOT have an infinite baffle. Of course, in a realistically sized room, you cannot actually have a true infinite baffle, since it would have to extend several full wavelengths in all directions, and he wavelength for 20 Hz is nearly 57 feet.... In all real-world studios, the actual baffle size is somewhat less than "infinite"! And that's fine, because there are some "tricks" that can be used to make it "seem" bigger than it really is, as far as he sound waves are concerned. But even a simple baffle without any "trick" will still reduce the effects of those nasty things.

What I call the "wing" is one of those tricks: the "wing" is the part that extends from the outer edge of the soffit baffle per sé, out to the side wall. The angle is different from that of the actual baffle. In addition to helping create the RFZ condition, it also makes the baffle "appear" wider, for low frequency waves.

Now, with a true 5.1 room, wings need very, very careful design, because they are also located exactly where the rear surrounds will produce high-level specular reflections back to the mix position! So 5.1 rooms and soffits are different from pure 2.0 soffits and room treatment.

(The guy who designed my studio had no absorption in front of about 3 feet behind my mix position. It was all very rigid. It worked well. But some people mentioned it was an outdated design.)

That's classic "LEDE" design. "Live End - Dead End". That's a concept that died 20 years ago! Nobody in their right mind builds pure LEDE rooms these days. Yes, they do work, but they are fatiguing. It's not natural to your ears or brain, and those have to work extra hard to make sense of nonsense. So at the end of the day, you end up feeling exhausted, without really knowing why. More modern design concepts, such as RFZ, CID, NER, etc. are mostly extensions of the LEDE concept, that keep the same basic goals in place, but achieve it in different ways that are NOT fatiguing, like LEDE is. The people who told you it was outdated are absolute correct!

Depending on how well I'm interpreting REW the modal region is surprisingly even in frequency response with the only worrying dip at 2-1-1. However, sustain is off the charts in the first two octaves and bass response to the ear is anemic. It is not tracking the signal in any useful manner.

Yup! Typical bass problems for small rooms that are untreated (or poorly treated), and not laid out optimally.

There's likely a LOT more in the REW data that you maybe haven't see yet. Post the MDAT, and I'll take a quick look when I have a chance.

Trying to interpret the ETC with string has lead me to believe that the first BIG reflection is coming off the front wall.

That's unusual! I'd bet that your first big reflections are coming from the side walls, and floor, and perhaps the ceiling. What you might be seeing, is SBIR. That's not really a "reflection" as such, but rather a phase cancellation of a reflection. And it will always be very low down on the spectrum: it is governed by one thing alone: distance between the speaker face, and the front wall. I'm not sure if you have seen the "walking mic" test instructions? If not, try that process, and you'll easily identify SBIR... as well as several other issues.

* Design soffit and place speakers. Baseline room.

Actually, it would be better to do that the other way around! First test the room extensively with REW, then based on that figure out the best locations for the speakers and mix position. Then design the soffit accordingly. A comprehensive set of REW data should lead you to good locations for your ears and speakers. Then everything else falls into place around that.

* Design soffit and place speakers. Baseline room.
* Build corners, cloud, and desk. Measure.
* Build soffit. Measure.
* At this point I'm really getting lost, but I had intended to use the side walls (wings?) to absorb early reflections at ear level and introduce early reflections at floor level -built deep enough for more bass trapping with the bottoms sealed in attempt to use slat spacing to do some additive narrower modal absorption. Measure.
* Continue to build floor to ceiling traps all the way around. Install slats on lower sides. Measure.
* Try to figure out how to align decay times and introduce liveliness that I suspect will get lost with so much bass trapping. Measure.
* Repeat.

It sounds like you are attempting to combine several design concepts at once! I would suggest just choosing one, and designing the room from that basis. It is possible to "mix and match", yes, but I find it easier to just set an acosutic goal, then follow a concept that will achieve it. Personally, I feel that the RFZ concept makes the most sense all around, and I use that as the basis for most of the rooms I design... with some of my own modifications! But others prefer different design concepts. As long as you stay consistent to the overall approach of the design concept you choose, then you should be good results.

In fact, all of the best design concepts have the same goals in mind: pretty much as defined in ITU BS-1116-3 and EBU Tech.3276. Meet either of those, and your room will be fantastic. That's not easy to do, but getting close to those specs will still get you a good room.

And the real truth of the matter is, I learn much better in practice. Once I have experience the more sense the reference material makes. Plus, my math skills are nil.

You don't need a lot of math, actually. Some, yes, but nothing too complex. Just basic high-school stuff. What I find to be more important that the math, is to understand the concept that the math explains. Simple example: W=c/f. Wavelength is speed of sound over frequency. Math makes that sound complex, but understanding it makes it simple: sound waves move at a constant speed through air, sound waves consist of "cycles" of high and low pressure, so it is logical that there must be a certain distance between one wave "cycle" and the next wave "cycle" that comes right behind the first one. The distance between those two "cycles" is the "length" of the wave, and it makes sense that you can figure that our by seeing how fast the wave goes, and measuring how many cycles it has in each second. Thus: wavelength is the speed of sound divided by the frequency. So, if you know that the wave is traveling at 1100 feet each second, and you get ten waves arriving every second, then the distance between them must be 1100 / 10 = 110 feet. It's a lot easier to understand the equation, when you have a mental picture of what is going on!

I find acoustics fascinating and beautiful but it's not my first concern here.

Hmmm... It should be! Not in the sense that you need to understand the equations for triple-leaf isolation walls, but in the sense that the very reason why you even have a studio, is because you want to listen to clean, clear, precise sound: and achieving that, is called "acoustics"!

If I had ample funds you'd be on your way to my new property at your next calendar opening.

Well, I've been to Las Vegas many times (I used to attend the famous NAB trade show every year), and I sure wouldn't mind going back again! But actually there's no need. In fact, I very seldom go to the locations of studios that I design: with modern technology, it is entirely possible to do the entire analysis, design, tuning and tweaking remotely. The Internet makes that possible, along with tools like REW and SketchUp, as well as Skype, Zoom... and the plain old telephone! That makes things MUCH cheaper for clients: paying for a studio designer to hop on a plane and do a site visit is a huge expense... and unnecessary! (Except maybe in unusual cases). It's much less expensive to just pay for the actual consulting service, or specific design. I do like to travel, as much as anyone, but it isn't justifiable for the vast majority of my clients to pay for my time and expenses to do that. I try to keep costs down for my clients, since money doesn't grow on trees!

Ooh, another thing I overlooked concentrating on the wrong aspect. I have a huge dip at what seems to be caused by 2-1-1 centered at what seems to be 0-0-2. So I was trying to get the absorption down below 140. That gave me two air gaps, one in the trap and one between it and the ceiling. Am I correct in thinking that the hardback and slant will redirect residual energy to the rear of the room? Do I want it less absorbent?

The hard-back accomplishes a couple of things at once: yes, it does reflect some energy at some frequencies towards the rear of the room, where it should be somewhat absorbed and somewhat diffused before arriving back at your ears after the ITDG, but that is frequency dependent, speaker dependent.. and angle dependent! You need to get the tilt angle correct to ensure that you really are getting a good RFZ around the mix position, in the vertical plane. The other thing that the hard-back can help with, is some modal issues: if it is large enough, and suitably located, it can have an effect on "smearing" the modes a little: basically, lowering and broadening the Q. It can do other things to, when used creatively...

My desk is unruly and I don't know that lowering it will be easy,

Careful with big chunky desks that sit up high! They have a profound (and detrimental) effect on room acoustics! A bad choice in desks can really undo a lot of the hard work you put into the rest of the room. The best concept for a desk is low profile, "open" construction, and no large, flat surfaces. Especially vertical ones. Angles are good, holes are good, and keep it all down low: no shelves or gear sticking up. Like this: The Soundman M1 studio desk

Thanks again for your attention to the subject and contribution to the world. Sound is too cool to not enjoy at it's best.

Very true! Getting your acoustics under control, approaching BS-1116-3 specs, will certainly accomplish that!

- Stuart -

Soundman2020 wrote:Getting into the theory a bit also helps! Not necessarily the math (although that can be very revealing too), but rather basic concepts.

Absolutely, but I think the term, "Knows just enough to be dangerous." applies in full force here. It seems like all of my assumptions are entirely off base. If I keep reading without putting thought into motion I just confuse myself further.

Right! Several superchunks in fact: it's a small room, and as you already noticed, the bass isn't behaving very well. Taming problematic bass needs a lot of treatment. Especially if you plan to use only porous absorption for the bass.

The only reason I would use porous only is that I am apprehensive about designing and placing membrane or Helmholz accurately. This is also one of the reasons I am here. If it does turn out that pressure traps will be advantageous then I would like custom designs. Going back to the first point, it will be far more costly to make many mistakes.

What will change most from different speaker positions is the amplitude of the modes and other resonances, but the relationship between frequencies won't be hugely different, and neither will the decay slopes. Those are room-related, mostly.

I wouldn't have put that together. Nice. I expect that would be the case at any position in the room regarding the low end.

One other point about your speaker angles: you might find this useful! : Speaker setup, and the equilateral triangle

I am happy to say that I can't remember a time when I didn't angle speakers like that.

Hmmm... not so good. Quick question: do the walls in your room coincide with the walls in the room below? Asked another way: are your walls directly above the walls of the downstairs room? If so, they they might be load-bearing walls, which can help to a certain extent. But your best bet would be to get a structural engineer in there to take a look, and tell you what your loading can be.

I looks like the room that moves, plus a bathroom and two closets are floating over the living room. The master has walls under 3 sides, the back wall is the one without. I'll get somebody in.

That would probably work: it's a bit on the light side, but should be OK. Question: You are going to use two mains plus a sub most of the time, correct? In other words, the mains won't be producing the low end, but rather the sub will be handling that?

Every once in a while I have a task that I decide would be better on just two speakers. Not often, and reconfiguration is quick and painless. So, yes. Subs most of the time.

I know that 5/8"+3/4" will be rigid, but will it be massive enough?

As I mentioned above, its on the low side, but probably in the ball park. However, it's not just the mass by itself: you also need rigidity. In other words, you don't want the baffle flexing and vibrating: it should be immobile across the entire face. Your support system doesn't seem to accomplish that: it only provides support at a couple of spots on the baffle, leaving the rest of it free to "shake, rattle, and roll"...

Yeah, I scratched those legs once I read the very first response in this thread. I just don't have a replacement yet. How much clearance is necessary between the soffit and speaker? Depending on green glue thickness maybe I could go 0.688"/GG/0.750" if that would make a significant difference.

In fact, very little of the total motion of a speaker is up-and-down! If you rest it in Sorbothane pads, then that's mostly what you are isolating: up-and-down motion... which isn't normally too much of an issue. Most of the motion is front-back, but there can also be side-to-side motion, and certainly vibration.

Well... it seems kind of obvious when you put it like that...

There's likely a LOT more in the REW data that you maybe haven't see yet. Post the MDAT, and I'll take a quick look when I have a chance.

My toe isn't even near the pool yet when it comes to understanding REW. I am not a system engineer so REW is actually my introduction to analysis software. (Frequently, at work, I walk by someone using SMART.)

I looked at my first baseline mdat and realized that I had used two subs and left the door open as that's how I usually work. I redid the tests. Happy to say the new line up with the previous. I did one sub, two sub, door open, door closed. Wow, the door... I will have fun looking these over. The sub is not haphazardly placed but I won't say it can't be better.The attached mdat is in your format. No extra measurements.

That's unusual! I'd bet that your first big reflections are coming from the side walls, and floor, and perhaps the ceiling. What you might be seeing, is SBIR. That's not really a "reflection" as such, but rather a phase cancellation of a reflection. And it will always be very low down on the spectrum: it is governed by one thing alone: distance between the speaker face, and the front wall. I'm not sure if you have seen the "walking mic" test instructions? If not, try that process, and you'll easily identify SBIR... as well as several other issues.

I will do the walking mic test next. I need to remove the desk as the center speaker is currently sitting on it and the video monitors are actually directly between the three speakers. I won't be able to get to the front wall with measurements the way it is. Even if that's not necessary, I want to look at the results. Hopefully it will help me in learning to interpret some of the graphs.

Actually, it would be better to do that the other way around! First test the room extensively with REW, then based on that figure out the best locations for the speakers and mix position. Then design the soffit accordingly. A comprehensive set of REW data should lead you to good locations for your ears and speakers. Then everything else falls into place around that.

I might actually be starting to understand the logic of this.

It sounds like you are attempting to combine several design concepts at once! I would suggest just choosing one, and designing the room from that basis. It is possible to "mix and match", yes, but I find it easier to just set an acosutic goal, then follow a concept that will achieve it. Personally, I feel that the RFZ concept makes the most sense all around, and I use that as the basis for most of the rooms I design... with some of my own modifications! But others prefer different design concepts. As long as you stay consistent to the overall approach of the design concept you choose, then you should be good results.

Thanks for the focus. Back to the "...just enough to be dangerous." concept, I was refreshing my memory on some of the different designs. I have a basic picture of RFZ in my head now. I also think I see why it would be a better concept in a room my size.

In fact, all of the best design concepts have the same goals in mind: pretty much as defined in ITU BS-1116-3 and EBU Tech.3276. Meet either of those, and your room will be fantastic. That's not easy to do, but getting close to those specs will still get you a good room.

I looked at those and have copies locally.

Hmmm... It should be! Not in the sense that you need to understand the equations for triple-leaf isolation walls, but in the sense that the very reason why you even have a studio, is because you want to listen to clean, clear, precise sound: and achieving that, is called "acoustics"!

That's what I was getting at. I couldn't do my job without a base level understanding of acoustics and phsycoacoustics. It's just that, statistically, I don't have enough time left on this planet to really study acoustics. I'd have to start with Math 101. That being said, my understanding of acoustics is scattered, outdated, and probably colored by instincts derived from my working habits.

Well, I've been to Las Vegas many times (I used to attend the famous NAB trade show every year), and I sure wouldn't mind going back again! But actually there's no need.

Thanks for coming out to attend! At least 30% of my work is (was) on the trade shows. Now that you mention it, I can see how tools like REW have changed your world. We live in the future. I love the fact that I can print mix revisions while I'm on the phone with a client. "That should be in your inbox now."

My desk is unruly and I don't know that lowering it will be easy,

I shouldn't have said that out loud without clarifying what I meant. I guess now is as good a time as any to come out of the closet with my desk. It's not too high, but my chair is incorporated. My ears are 48.5" off the floor. So to cover the floor with wood would mean trimming up the bottom of the desk. Which, I don't think is possible. Glues and screws and such.

From the beginning I have always wished that tracking and mixing rooms were different facilities. The big consoles are a bear to mix around and as soon as it was feasible I ditched mine. Early 90s I should think. I have been designing and building desks like yours for decades. (Less the legitimate acoustical concepts. But they look almost identical.) I even go one step further by recessing the video monitors. Nowadays I have two pieces of rack gear and both can be remote. (Speaker control is in software.) So I don't need, nor will I build wings on the desk. I am always baffled when I see pictures of studios that are obviously mixing in the box, so they have ditched the console, but then built a giant work surface the same size as the console or bigger!

Oh, back on topic. My desk is a <cough> racing cockpit </cough>. I only have one room to both work and play. I am very much a racing enthusiast. I race IRL and virtually nearly every month of my life. It is the one thing I will not compromise on in the room. That being said, the desk is currently built to support three video monitors at eye level. I went VR over a year ago. Once I hack off the top of the foot well it will be truly low profile acoustically. The only surface higher than 27" is the wheel mount. However, it also needs rigidity for muscle memory and accuracy so I'm thinking of rebuilding it with aluminum frame rather than routing the sides.



I think my main question is where do I start?

* Walking test without desk.
* 3 superchunk in the corners then walking test without and then with desk. + second baseline.
* As you said above, find the speaker/ear locations.
* Should I put the floor boards down as soon as possible?

Looking at SPL only, I notice that there is a dip at 78Hz in the left and right speakers only. 43" is the 1/4 wave length of 78Hz which is the distance from the acoustical center of the speaker to the side wall. Add the sub and it smooths out dramatically. The dips between 97Hz and 131Hz appear in all measurements. Am I looking at evidence of SBIR in the former and modal interference in the later? SBIR being a phenomenon that also takes place regardless the listening position?


I'm gonna study these plots and see if I can come up with an assessment of the room that is somewhat aligned with reality.

Mark

Starting To Build

What are my goals?
* Isolation is really not a concern to me. I have spent most of my adult life making good sound in noisy environments. Truth be told, a little background noise helps me make those last adjustments that might otherwise be missed.
* Only one person will ever be in the room.
* The bass is out of control. Flat isn't too much of an issue as I have had good success with the Geddes method. (Unless that's a bad idea in a mix room.) But there are some big dips in the fundamental range that I can't live with. Gentle EQ on gentle peaks is OK with me.
* Early reflections are out of control. I'm interested to find out how much can actually be done in a room this size.
* Door in the rear corner is nasty. I just put 3 superchunk and it really threw off the symmetry of the response.
* Frequency response. I have always liked a bit of downward tilt. 3-6dB, depending on the environment, between 80Hz and 8000Hz.
* Decay times need to be even. Although I haven't noticed my personal preference, lower and smooth tilt sounds alright to me.
* At this point I have an embarrassingly low amount of cash. All the music venues are closed, but I have mix and sound design work barking up my tree. I've got to switch gears.

It's been a heck of a week. I had to take the desk into the garage to chop it up and aerate it. We've been setting heat records here in Las Vegas NV USA. Average temps at my house have been 115 F. That means it's been 125 F in the garage. So working out there has been an exercise in how to slow all of my movements. On top of that, I rest and drink water every third move. So... measure, mark, cut, stop, drink. Glue, assemble, clamp, stop, drink...

I've been playing Team Ketchup in acoustics. I love this forum. For some reason I've gotten better understanding here than elsewhere. Perhaps it's simply because it's so new there is less unproductive argument over semantics and/or questionable info having become the popular ideas. Unfortunately, the more I grasp the basics, the more I realize that in order to design a room that works one needs a big picture understanding. That includes knowing the effects of specific designs and how they interact with the environment.

I've also been inspired by the most basic stimuli. I have assisted on several studio builds over the years. Not the least of which - I assisted from start to finish on my own ground-up recording studio. (My ex-wife now has one of the best sounding pool rooms in New Mexico.) I always get a kick out of how this, that, or the other fixture acts in the acoustical space and like to put my ear up next to them. It seems like building these things is a bit like twisting the knobs on a parametric EQ. It's more pure though. Beautiful.



I had the room empty and moved the speakers around some and did some measurements. I literally wore out a metal tape measure. There are kinks every few inches along the first twelve feet. If I'm not careful extracting and returning it I will cut my fingers. This is a small room. If I get too far off the front wall that back wall starts crowding me. I can't go too close to the front wall or I won't be able to get my center speaker far enough away. The best listening position seems to be very sensitive to within a few inches at best. The more I fidget and measure the more I start to wonder if the soffit won't change everything? How do I know the best position when the soffit is not in yet.

In the attached mdat the measurements 66b and 60 PI were of the greatest interest to me. I chose to go forward, for the time being, with 60 PI based mostly on the early reflection levels.


desk LRS Baseline - Where I set everything when I moved into the room.
90b LRS Baseline - Same position but with the desk removed. Woof!


66b LRS Baseline - Is this even good? I felt like I was getting somewhere at the time.
60 PI LRS Baseline - I thought I liked everything about this better, but I still have a ways to go in understanding the ramifications of the graphs.
60 SC LRS Baseline - 60 PI LRS Baseline but with superchunk in 3 corners.

The first thing I noticed after the superchunk was increased ineligibility in the low end. Not by any means perfect, but at least I can tell what's going on. There seemed to be more dynamic range and space in the room. And more clarity along most of the frequency range.

After measuring with REW I was initially confused by what I was seeing. There were greater dips and peaks in places. Looking at the REW screenshot below I noticed that the dip at 84Hz with superchunk corresponds to 1.0.0 and the peak at 89Hz corresponds to 0.1.0. (All of the sudden they're looking a little close for comfort.) Considering that the mic was dead in the middle between the side walls and 18" forward of the middle lengthwise I'm thinking the energy of 0.1.0 was masking the dip at 84Hz? Is masking the correct term there? The next biggest green peak is at 168Hz which would be 2.0.0 if my thinking is right.


Then there is next section of dips between 103Hz and 128Hz which I think might be SBIR as they move dramatically in the walking test.

The next big green peak is at 168Hz. That would be 0.2.0? But why the greater summation?


Looking at the waterfalls and spectrograms it is clear that pink fluffy has an effect on the space.

There is a 'tone' at 144Hz that pops up in certain measurements and rings with almost perfect sustain at 45 or 50dB. It's not in all measurements. I have yet to figure out what it is.

Also, early reflections have increased by a couple of dB. Is there now more room to move in the room? Not so much pressure filling the volume?


This is hard...

Mark

The main elements of the Reflection Free Zone design concept are pretty straight forward. I have found several explanations that make it clear to keep early reflections below a certain level within an initial time gap, 20ms typically, and allow a diffuse field to support our natural expectations above the gap. By my reckoning this is fine and dandy in a room that's 40 feet deep. But I am struggling to figure out how to make it work in a room where the back wall is 8' 6" from my ears. Everywhere I look it is said that small rooms can't have enough bass treatment. But if I put 12" of material around 5 walls I'm sure it will be too dark. Which leads to the problem of how to design and place fixtures that do the right amount of damage but not too much. I have run headlong into Kyle's E Chord. I'ma strummin' - but it aint pretty.

One thing I did find in the last couple of weeks was Stuart's posts in the Barefoot soffit thread. That has eased a lot of my anxiety over mounting the speakers. I was overthinking the process and had imagined pulleys and ballast and all sorts of nonsense that don't need to be the case. I'm still puzzled by the math, but the materials I can work with. I'll explain in a bit.

So my starting point is a soffit in 9 pieces in a room. Sitting on 3 sheets of MDF. Three corners filled 32" across with super chunk. An angled cloud above with a hard back. Absorbent side walls. Absorbent back wall.


Naturally, this leads me to even more questions.

The back wall, if I've got the right idea, is pretty straight forward. Bass attack. Using Safe N Sound and AMCalc it seems like 3 inches of SnS, 3" air, 3" SnS, and 3" air gives me the best low end performance. So that's what's in the drawing.

In this graph, the 9" trap is SnS/air/SnS/air as described above. The other three are simply one layer of material 1/2" from the wall.


The side walls are a bit harder for me to conceptualize. At first I was thinking that perhaps it's a job for 705 or 703 in an effort to keep some of the ambiance in the room. Then I thought, no, those early reflections will take away my ability to make good decisions, I need to wipe them all out. I don't have any practical experience to guage the difference between 0.86 and 0.93 absorption coefficient at 1000Hz. Perhaps I should go with max absorption and then use less surface area. Make them 5, or 6 feet tall and leave some wall to reflect? They will need to be free standing as there is a double sliding glass door on one side.

Reading Stuart's 2008 or so description of how to mount the speakers makes me happy. Basically build a box with exact clearance on all sides. Cut sorbothane to deflect the right amount under the weight of the speaker with the added pressure caused by sorbothane on the top of the box pressing down. The sides of the box are distanced to deflect the sorbothane the right amount laterally. Nice. Straight forward. My 2 questions here are; How on earth do you calculate how much weight will be added by the top of the box? Does the side pressure relieve the need for blocks on the back of the speaker limiting fore/aft movement?

And.... I got my head into a place with more wiggle room than there was previously and set to placing my speakers better. Where they are now sounds much, much better when playing any program including, and of course, music. Oddly, the measurements seem to be slightly worse all the way around. Higher early reflections, not quite as even decay times, slightly higher peaks... but it really does sound miles better.

The measurement names in this file are all messed up. I changed convention part way through. That being said, I have detailed notes as well as full measurement sets for each. "6660 LR-S-- Base" is the placement that I currently think sounds best.


Then I started thinking about the soffit. OY! My brain hurts. In the drawing above the height of each section is arbitrary. All of it place holders for the most part. Can the cabinets fill the entire space, can they have acute angles on the interior? Or is square the best way to go? How far out do I want my shortest side? My speakers' electronics have a roll off centered at 50Hz so 200 Hz is where they start rolling. The filter is all the way in now and I wouldn't mind reducing any boost below 250Hz. How do I terminate the soffit? Should there be a bevel? Heavy absorption? Hard sided cabinet? Are the wings all absorption? Or should they be more reflective angles?

[EDIT] I forgot to clarify what's going on in the drawing. There will be 3 soffits, each consisting of 3 cabinets bolted together. I only drew one stack in the drawing, the footprint of a second, and baffle of one. I am familiar with the idea of leaving 6mm air around the speaker and 12mm between speaker and baffle and how to balance the speaker in the box. But how does the baffle attach? Is it simply bolted to the cabinet?

Oy...




Mark

I have found several explanations that make it clear to keep early reflections below a certain level within an initial time gap, 20ms typically, and allow a diffuse field to support our natural expectations above the gap.

Right! 20ms at least, 30ms or more ideal, and it's not just the early reflections, but all reflections, to one degree or another.

By my reckoning this is fine and dandy in a room that's 40 feet deep. But I am struggling to figure out how to make it work in a room where the back wall is 8' 6" from my ears.

Bingo! That is, indeed, the problem! It is impossible to get a 20ms delay for a wall that is only 16ms away.... So for a small room, you just have to do the best you can to get those first reflections as low as possible in intensity, and as diffuse as possible... but that leads to the next problem: if the first reflections are basically dead, then there's no diffuse field either! But you need a diffuse field... and you can't even use most types of numeric-based diffusion anyway, directly behind you, since you need at least ten feet between the face of the diffuser and your head, to ensure optimal smoothing of the diffused lobes and things.

It is, indeed, a complicated issue with no ideal solution, for a small room. The goal then is to just get as close as you can.

Everywhere I look it is said that small rooms can't have enough bass treatment. But if I put 12" of material around 5 walls I'm sure it will be too dark.

It would also be a mistake to do that! Yes, I know that some places tell you that you should, but that's not the best way of getting the results you need. Killing the side walls and ceiling is a bad idea: the rear wall is the key.

That has eased a lot of my anxiety over mounting the speakers. I was overthinking the process and had imagined pulleys and ballast and all sorts of nonsense that don't need to be the case.

Right! The concept isn't that complicated, and the implementation doesn't have to be overly complicated either.

I'm still puzzled by the math, but the materials I can work with

Me too! That's why I wrote a Dynamic Component program in SketchUp, to do most of the hard work for me. It took me many months to get right, and I went crazy for a while figuring out all that math and putting it into the program, but now it's a hell of a lot easier for me, because it does all of that automatically, based on the parameters I feed it. I can then adjust things a bit if I don't like the way it worked out in the room, and it will then re-calculate everything for the new parameters. It takes a lot of the drudge work out of designing the mounting details for the speaker in the soffit. Of course, the result is only as good as the parameters I give it! But at least it does the math for me.

Three corners filled 32" across with super chunk.

If you are going to soffit-mount your speakers, then there won't really be much space to build superchunks in those two front corners. At least, not enough space to make them large enough to be effective. I normally do hangers in the corners, as well as above and below the speakers themselves. They are quite effective.

An angled cloud above with a hard back.

Definitely! Do make sure you calculate the angle correctly! And do leave some adjustment on the chains when you hang that, so you can change the angle again, if need be, after the first REW tests.

Absorbent side walls.

Only on the first reflection points! And maybe some additional panels to deal with flutter echo, if you have that problem. But not the entire side wall. If you make your side walls completely absorptive, you will end up with a very dull and lifeless room, and a "hole" around 250 Hz that will be difficult (if not impossible!) to fix.

Absorbent back wall.

That's where you should concentrate a major portion of your treatment effort. The rear wall is the key, in pretty much any room. That's where a large chunk of your problems will be, so it is also where a large chunk of your treatment should be.

The back wall, if I've got the right idea, is pretty straight forward. Bass attack. Using Safe N Sound and AMCalc it seems like 3 inches of SnS, 3" air, 3" SnS, and 3" air gives me the best low end performance. So that's what's in the drawing.

That's only 9": not very much, when you need to get down low. In theory, 9" will have some absorption down to around 90 Hz, but you need to go a lot lower than that. Your room will have serious modal stuff giving you problems, down to much lower. 9" would be fine for the center of the rear wall, but you should go more like 36" in the corners. 24" at least. 24" will, in theory, get you some absorption down to maybe 40 Hz.

Of course, the big problem with having such a large area of absorption that covers the entire spectrum, it that it will suck the life out of the room! You can see on your graph that you might be getting 0.65 alpha at 100 Hz, for example, but you are also getting around 1.0 alpha for everything above 3 kHz. So the room will sound very dead. You need to do something to return the missing mids and highs, but diffusely.... or at least, not specularly.

I don't have any practical experience to guage the difference between 0.86 and 0.93 absorption coefficient at 1000Hz.

Not a lot, to be honest! It's the difference between about 17 dB and about 23 dB reduction in the intensity. In reality, the limit is about 20 dB: even though the alpha numbers tell differently, it isn't realistic to expect more than about 20 dB attenuation from porous absorption. However! Once again, there is frequency involved, and depth. The thinner it is, the less of the spectrum it covers, and to cover down deep, it has to be unrealistically thick, and also not too dense.

This is why it is impossible to create an RFZ with absorption alone: sometimes people try to do that, but it isn't realistic. You can't get enough spectrum coverage, nor enough attenuation, from realistic absorption, and instead of getting th RFZ you wanted, you get a dull, dead, unbalanced, lifeless room that is unpleasant to work in.

Which is why I usually design soffits such that there are no first reflection points, and therefore no absorption is needed at those points. In a decent sized room, that is usually possible. But sometimes for a small room, there is still a need for absorption on the first reflection points.

Basically build a box with exact clearance on all sides. Cut sorbothane to deflect the right amount under the weight of the speaker with the added pressure caused by sorbothane on the top of the box pressing down. The sides of the box are distanced to deflect the sorbothane the right amount laterally. Nice. Straight forward.

That's basically it, yes.

My 2 questions here are; How on earth do you calculate how much weight will be added by the top of the box? Does the side pressure relieve the need for blocks on the back of the speaker limiting fore/aft movement?

2 answers:
1) It's complicated, because it isn't really weight, but rather pressure. The weight of the top panel is irrelevant here: it's the pressure that it will apply once it is in place. It applies that pressure to the top of the speaker,and also therefore to the pads under the speaker. Thus, the ones at the bottom have to account for the weight of the speaker, and also the extra pressure applied by the top panel.
2) Yes. There's enough resilience in the side pads that they also resist and damp the front-back motion, and in my design there are also front pads... you just cant' see them with the baffle in place! I thought about doing rear pads as well, but found it to not be necessary. Of course, when you calculate the resilience for the front/back motion, you have to take the lateral dimensions of the pads into account, not just the thickness.

It's complicated!

Then I started thinking about the soffit. OY! My brain hurts. In the drawing above the height of each section is arbitrary. All of it place holders for the most part. Can the cabinets fill the entire space, can they have acute angles on the interior? Or is square the best way to go? How far out do I want my shortest side?

Yup! All that, and much more, you need to take into account. And don't forget ventilation: you do need to allow for plenty of cooling air flow around the speaker! Don't make the mistake of only having airflow up the rear face.... I've seen some designs like that, and it leaves you wondering.... The entire speaker gets warm, not just the rear panel. Yes, there's a heat sink on the rear of many active speakers these days, and that does get hot, but it's not the only part that gets hot. When you realize that speakers are only about 1% or 2% efficient (perhaps a couple more points for really good, exotic speakers), you realize that there's a hell of a lot of "watts" that end up as heat, not acoustic power. So, for example, if you are really pushing your speakers to pump out high dB range, and let's say they are consuming 500 watts of electrical power, probably around than 499 watts is being converted to heat, and you are only getting maybe 1 watt of acoustic power. So there's a hell of a lot of heat inside that box, that needs to go somewhere! If the only way out is through the front (driver cones) and the rear (heat sink), then you have quite a thermal gradient building up across the rest of the box.... Hmmmm. Ventilation is important. To be sure, you don't normally run your speakers full bore, roaring out at 110 dB, but the point is still valid: keep them cool.

My speakers' electronics have a roll off centered at 50Hz so 200 Hz is where they start rolling. The filter is all the way in now and I wouldn't mind reducing any boost below 250Hz.

For the room testing, and initial tuning after the soffit is built, set that flat. You don't need any of the speaker settings, if the speakers are properly mounted in soffits. The soffits eliminate the need for that (with a couple of exceptions).

How do I terminate the soffit? Should there be a bevel? Heavy absorption? Hard sided cabinet? Are the wings all absorption? Or should they be more reflective angles?

So many questions.... so many answers! A lot of that depends on what you are trying to achieve, and the room itself, and the speakers too. Even the furniture, to a minor extent. And a lot depends on the room "geometry": relationship between the speakers, mix position, and room boundaries. There is no "one size fits all" for soffits (or any other aspect of room treatment, for that matter). All rooms are different. Each has its own quirks and benefits and problems, so the soffit design should take that into account too. There can be a basic design concept for soffits that works in most rooms, but it still needs modifying to fit each specific case.

It also depends on how accurate you want the room to be: if you are going all-out to get it as good as it can possibly be, then EVERYTHING matters! But if you are happy with just a fairly decent room, and have no interest in chasing the specs of ITU BS.2226-3 or EBU Tech.3276 down to the last millisecond or tenth of a dB, then you probably don't need to go crazy about the soffit details.

- Stuart -