Garden Recording/Mixing Room in Surrey, UK - Build Diary

#46

OK. I'm back!

Combination of issues with my knee and the terrible weather we have been having has halted progress. Finally had an MRI and it has revealed that I need an ACL reconstruction. that is going to take me out of the game for quite a while so I need to get more of the studio done before the op (waiting for date)

Thankfully I did manage to get the roof finished on the odd day at the beginning of this month that wasn't frigid/raining. Pictures to follow.

#47

So, Back to the Vent boxes...

I think I have finally worked out a solution. I have calculated that I can fit in a box, on the inner leaf, at each side that is:

520mm width
280mm height
2400mm length

Using the beer mat calculations that you kindly put together, Jennifer, I have worked out:

Calculate Z: Start with 280mm height. Subtract 2 x 36mm for the double skin silencer box gives 208mm. Subtract 2 x 25mm for the duct liner gives 153mm

Calculate X

In Gregwor's box he uses the formula X = (Y - 7) / 2

The 7 represents 7 inches, and must be deducted to account for the size of the walls & duct liner as above, and also extra space to allow the internal baffles to overlap each other to some extent. Let's convert that to metric for our purposes:

2 x 36 + 2 x 25 + 75 = 197mm

With Y of 520mm that gives:

X = (520 - 197) / 2 = 161mm

Cross section through the silencer can now be calculated by X * Z:

197 x 161 = 24,633 mm2 ~= 246 cm2

A recap of one possible set of requirements:
Assuming 5 people and 75 cfm, the cross section area of the silencer can be calculated:

CSA = CFM/300 = 75/300 = 0.25 ft2 ~= 232 cm2

If my calculations are correct, 246 cm2 is more than adequate. Please correct me if I am wrong

I'll have to cut away some of the 2 joists to fit them in, as you can see below, but that is no issue as there is a supporting joist very close to both sides.

Please advise if you see any issues with this, otherwise I can move forward and start building them.

Cheers,

#48

the long pipe coming out of the box - if that is the supply (or return), then the opening and the pipe are still exposed to external noise and also allowing sounds to escape. you want the opening into the room to be on the box itself and sealed, and then the exterior-side pipe can be whatever length it needs to be since it's already exposed. so essentially move the box to the opening and put the hole on the bottom of the box.

#49

gullfo wrote:Source of the post the long pipe coming out of the box - if that is the supply (or return), then the opening and the pipe are still exposed to external noise and also allowing sounds to escape. you want the opening into the room to be on the box itself and sealed, and then the exterior-side pipe can be whatever length it needs to be since it's already exposed. so essentially move the box to the opening and put the hole on the bottom of the box.

Thanks Glenn; good catch.

Duh! that was rather silly of me. I did have it that way originally but didn't want the vent in the middle of the room so made that quick change without thinking about it too much. I will revert the design and have the return/supply outlets/inlets coming directly out of the box on both sides.

Cheers,

#50

Sorry to hear about your knee Sam, all the best for getting that sorted.

These silencer dimensions look good, nice one. How many baffles will you fit in these?

Glenn is correct about the location of that long pipe. What material will you be using for the correctly sited pipe by the way? I used 150mm diameter insulated flex duct for the equivalent duct here, with the notion it would decouple the outer leaf and fan from the silencer. I used the non perforated type. You can get perforated types that apparently have better sound attenuation properties, but those are not to be used in potentially damp spaces e.g. lofts.

Do you have a way of assessing the amount of fan noise you'll end up with inside the studio before covering the works in plasterboard? If this is potentially a concern it might be worth attempting. Glenn has mentioned building a silencer style box around the fan itself to reduce fan noise. This is something I would do if I had space, but it may not be necessary for your requirements.

Another consideration is the location of the silencer opening into the room. I had no choice other than to place mine near the tri-corners. I wonder if this amplifies low frequency sounds coming out the opening (e.g. fan rumble) in the same way it does when you put a speaker in a tri-corner? I've no idea if I'm putting 2+2 together here and getting 5, but it might be worth considering placing the opening away from a tri-corner.

Remember to size all ventilation grilles etc. appropriately to keep static pressure manageable.

Will you be using positive pressure (fan blowing in) or negative pressure (fan sucking out) ?

Cheers,
Jennifer

#51

you could use pvc if you decouple the pipe from the silencer in/out with a coupler of soft rubber and wrap the pipe with the duct liner to insulate (temperature) -- follow Jennifer's advice to use the flex duct.

on the fan - i prefer to have them outside the room and push and pull (supply and return) so the fan noise is part of the attenuation of the silencer job rather than in the room. but it will depend on your option to maintain them (fans need cleaning, or go bad) and if they're buried in the unit or inside the structure then maintain them becomes a problem.

#52

Makes sense. So unless you have easy access to the cavity, your options for siting the fan are either inside the room, or outside, presumably in some sort of weatherproof enclosure.

#53

endorka wrote:Source of the post Sorry to hear about your knee Sam, all the best for getting that sorted.

These silencer dimensions look good, nice one. How many baffles will you fit in these?

Thanks for the kind wishes, and assistance!

As I plan the boxes to be 2400mm in length (same as the length of the OSB boards I have to make life easier) and 520mm wide, I see that as per Gregwor's silencer design calculations:

Y=520mm = 20.4”

X = (Y - 7) / 2
= (20.4 - 7) / 2
= 6.7”

6.7” = 170mm

If I divide the box length by 170mm (rough calculations) I get 14. The liner will take up space so I'm thinking 13 baffles. Let me know if I have that wrong.

Glenn is correct about the location of that long pipe. What material will you be using for the correctly sited pipe by the way? I used 150mm diameter insulated flex duct for the equivalent duct here, with the notion it would decouple the outer leaf and fan from the silencer. I used the non perforated type. You can get perforated types that apparently have better sound attenuation properties, but those are not to be used in potentially damp spaces e.g. lofts.

Yes, I will be putting the outlet from the box directly in the room and having the long pipe going to the outer leaf/fan.

I'll be going on what you have recommended; the 150mm flex duct - This stuff looks great! https://www.justfans.co.uk/acoustic-alu ... -p-71.html - It will be situated in under the 'warm roof' so should not get damp.

Do you have a way of assessing the amount of fan noise you'll end up with inside the studio before covering the works in plasterboard? If this is potentially a concern it might be worth attempting. Glenn has mentioned building a silencer style box around the fan itself to reduce fan noise. This is something I would do if I had space, but it may not be necessary for your requirements.

Unfortunately not. I am happy to proceed and just live with the end result. If I get the quietest fan I can it should mitigate noise from that at least. Plus it will be me on my own for the majority of the time so can have low speed on the fan. Getting to a point where I need to get the project done asap. Once I have my knee op I'll be out of action for a while again.

Another consideration is the location of the silencer opening into the room. I had no choice other than to place mine near the tri-corners. I wonder if this amplifies low frequency sounds coming out the opening (e.g. fan rumble) in the same way it does when you put a speaker in a tri-corner? I've no idea if I'm putting 2+2 together here and getting 5, but it might be worth considering placing the opening away from a tri-corner.

Yes, I have thought about this. as the boxes are near the front right/rear right of the room (facing mixing position) I can have the outlets in the corners.

Remember to size all ventilation grilles etc. appropriately to keep static pressure manageable.

I assume you mean to keep the 150mm diameter with all duct and grills etc?

Will you be using positive pressure (fan blowing in) or negative pressure (fan sucking out) ?

I'm not sure what is best tbh. I don't want the cold air coming in over the mixing position, and as the fan will be situated over the door, rear right corner, I think pushin in the air on this side so that air is sucked above mix position is best.

on the fan - i prefer to have them outside the room and push and pull (supply and return) so the fan noise is part of the attenuation of the silencer job rather than in the room. but it will depend on your option to maintain them (fans need cleaning, or go bad) and if they're buried in the unit or inside the structure then maintain them becomes a problem.

Thanks. I plan to have the fan connected to the outer leaf under the roof on the outside of building (protected from the elements and accessible), basically the same as Gareth's room; we have an identical roof design:

As my fan will be in the same position as above, is it worth the extra expense of the Fan you have suggested, Jennifer (https://www.justfans.co.uk/silent-500150-p-1906.html) over Gareths one (https://www.justfans.co.uk/td500-mixven ... p-202.html)?

It's only £50 more but the difference is 27dB vs 35dB respectively (on max speed) I guess in the grand scheme of things a quieter fan, even if only by 8dB is probably worth it; what do you guys think?

Also, does this fan accept the speed controller (https://www.justfans.co.uk/speed-contro ... p-656.html - love the look of this bty, perfect for the soviet-style studio

, Jennifer? I can't find that info...

Thanks again for the support on this stuff!

Sam,

#54

BeardMusic wrote:Source of the post
X = (Y - 7) / 2
= (20.4 - 7) / 2
= 6.7”

6.7” = 170mm

If I divide the box length by 170mm (rough calculations) I get 14. The liner will take up space so I'm thinking 13 baffles. Let me know if I have that wrong.

I think you may have gone about this back to front - I'd work out the total length with a certain number of baffles and see if it fits. Your earlier X calculation was 161mm, so I'll go with that for the following off the cuff calculation.

2 end walls + duct liner = (36mm + 25mm) x 2 = 122mm
One chamber of X size = 161mm
One baffle is 18mm OSB + 2 x 25mm duct liner = 68mm

So if you have 10 chambers and 9 baffles this gives 1610mm + 612mm = 2222 mm
Adding end walls gives 2344 mm, which will fit within your size limit.

That is a boss of a silencer!

Yes, I have thought about this. as the boxes are near the front right/rear right of the room (facing mixing position) I can have the outlets in the corners.

Just to clarify, if my assumptions in the previous post are true, I would try to avoid placing the silencer outlet coming from the fan away from a corner to reduce corner based amplification of fan rumble. If you want the air to come out of a corner it is possible to run duct from the silencer outlet to vent in the corner.

Good location of the inlet and outlet to get ventilation throughout the room is important. I took the simplest approach which was to have one in the front floor left corner, the other in the back ceiling right corner. More sophisticated approaches with branches etc. are of course possible.

Whether you have fresh air coming in at the bottom or top alters things too. There's a bit in the Rod Gervais book about this; from memory, fresh air near floor is best if you are heating, fresh air near ceiling is best if you are cooling.

Remember to size all ventilation grilles etc. appropriately to keep static pressure manageable.

I assume you mean to keep the 150mm diameter with all duct and grills etc?

Nominally, yes. It is worth noting that the grilles will only have a certain percentage of their area free for air though, as part of it will be covered with fins or similar. So for example you may need a 200 x 200mm grill to get a free area equivalent to your 150mm diameter duct.

Will you be using positive pressure (fan blowing in) or negative pressure (fan sucking out) ?

I'm not sure what is best tbh. I don't want the cold air coming in over the mixing position, and as the fan will be situated over the door, rear right corner, I think pushin in the air on this side so that air is sucked above mix position is best.

That's good, as most applications favour positive pressure - see Gervais book for more details.

As my fan will be in the same position as above, is it worth the extra expense of the Fan you have suggested, Jennifer (https://www.justfans.co.uk/silent-500150-p-1906.html) over Gareths one (https://www.justfans.co.uk/td500-mixven ... p-202.html)?

It's only £50 more but the difference is 27dB vs 35dB respectively (on max speed) I guess in the grand scheme of things a quieter fan, even if only by 8dB is probably worth it; what do you guys think?

Assuming those figures are correct, 8 dB is a lot! To hear the effect, fire up some pink noise through your monitors at a decent volume from your DAW or REW. Then reduce it by 8dB. Very noticeable - I'd easily pay ten times that amount for such a reduction!

Recall also that Gareth's build used 4 silencers in total, two on each leaf, so likely has a better fan noise reduction that you will get. This also points in the direction of the quieter fan.

Also, does this fan accept the speed controller (https://www.justfans.co.uk/speed-contro ... p-656.html - love the look of this bty, perfect for the soviet-style studio , Jennifer? I can't find that info...

I love the look of it too! No idea if it will be appropriate or not. The key is to get a variac controller. Normal dimmer type controllers will generate hum.

#55

to add some -- generally having the air entry on the "door side" but centered over the console or couch -- this makes any air vent or movement noise behave more symmetrical in the room. then the return (exhaust) farthest away. this will cause the (generally) correct air flow whether the room is fed from an open door (or window) or the supply. this is important because if you have a situation where doors are opened a lot or regularly, this can end up with air pockets of stale air. so a good cross-movement of air to remove co2 and distribute the oxygen is important. in large enough rooms i'll split the supplies and returns across multiple locations.

#56

Also, have you thought about an air filter? If you're going to use one it should be before the fan inlet to prevent dust & debris being drawn in to your studio.

I used an inline filter box like this and it was easy to install. After a while in use a significant amount of debris had accumulated on the filter itself, requiring replacement, so I'd say it was worth considering.

https://www.justfans.co.uk/duct-mounted ... -2946.html

#57

another consideration (#moreExpensive) is an ERV unit to manage humidity and preserve energy (transfer temperature across inbound and outbound air), as well as a filter. basically a single unit which pushes fresh (relative thing if you're in an urban area) and pull stale air.
some info: https://www.ecohome.net/guides/2276/cho ... nd-an-erv/

#58

And yet another consideration before you commit to the fan would be estimating the static pressure of the entire system - grilles, ducts, silencers, filters etc. You can use this with the datasheet for the fan (linked below) to determine the likely air flow rate at different fan speeds.

If you'd like some help with this let me know and I'll post my workings here. Some static pressure values can be accurately derived from manufacturer test data for filters, grilles and duct. The silencers are trickier and based on estimates. IMHO is there is any doubt whatsoever that your chosen fan might not be up to the task, go for a more powerful model. You can always run it slower if it's over specified.

https://www.justfans.co.uk/pub/EN_TD-SILENT.pdf

Cheers,
Jennifer

#59

Sorry for the delay in responding; work/life has been crazy this week...

Thanks for the feedback! Some answers below:

endorka wrote:Source of the post

I think you may have gone about this back to front - I'd work out the total length with a certain number of baffles and see if it fits. Your earlier X calculation was 161mm, so I'll go with that for the following off the cuff calculation.

2 end walls + duct liner = (36mm + 25mm) x 2 = 122mm
One chamber of X size = 161mm
One baffle is 18mm OSB + 2 x 25mm duct liner = 68mm

So if you have 10 chambers and 9 baffles this gives 1610mm + 612mm = 2222 mm
Adding end walls gives 2344 mm, which will fit within your size limit.

That is a boss of a silencer!

Yea, I wasn't exactly sure how to calculate it correctly; 9 baffles (the walls inside the silencer I assume) sounds good. I can just divide the inner area equidistant to the 9 baffles. PLeased you think it will be a Boss of a silencer; as I'm only going for 2 (as opposed to Gareth's rig) I think they need to be substantial!

Yes, I have thought about this. as the boxes are near the front right/rear right of the room (facing mixing position) I can have the outlets in the corners.

Just to clarify, if my assumptions in the previous post are true, I would try to avoid placing the silencer outlet coming from the fan away from a corner to reduce corner based amplification of fan rumble. If you want the air to come out of a corner it is possible to run duct from the silencer outlet to vent in the corner.

Good location of the inlet and outlet to get ventilation throughout the room is important. I took the simplest approach which was to have one in the front floor left corner, the other in the back ceiling right corner. More sophisticated approaches with branches etc. are of course possible.

Whether you have fresh air coming in at the bottom or top alters things too. There's a bit in the Rod Gervais book about this; from memory, fresh air near floor is best if you are heating, fresh air near ceiling is best if you are cooling.

What I planning is to have the outlet/inlet grill on the actual boxes themselves, if you imagine on the pic below, as the end of the boxes fall roughly in the center of the room (front and back) this seems to be a good placement for them room-wise. Left one (rear) will be over the sofa at the rear of the room (Setting up the room facing the long dimension) and the right one (front) will be over the mix desk:

I can create a better image if that is not clear.

Remember to size all ventilation grilles etc. appropriately to keep static pressure manageable.

I assume you mean to keep the 150mm diameter with all duct and grills etc?

Nominally, yes. It is worth noting that the grilles will only have a certain percentage of their area free for air though, as part of it will be covered with fins or similar. So for example you may need a 200 x 200mm grill to get a free area equivalent to your 150mm diameter duct.

OK. not sure how to calculate this, as I siad I was planning on just having 150mm outlet/inlets on the boxes in the room. I could make them 200mm wide if that helps.

Will you be using positive pressure (fan blowing in) or negative pressure (fan sucking out) ?

I'm not sure what is best tbh. I don't want the cold air coming in over the mixing position, and as the fan will be situated over the door, rear right corner, I think pushin in the air on this side so that air is sucked above mix position is best.

That's good, as most applications favour positive pressure - see Gervais book for more details.

Sticking with this idea. Don't want cold air pumping down on my head in the mix position.

As my fan will be in the same position as above, is it worth the extra expense of the Fan you have suggested, Jennifer (https://www.justfans.co.uk/silent-500150-p-1906.html) over Gareths one (https://www.justfans.co.uk/td500-mixven ... p-202.html)?

It's only £50 more but the difference is 27dB vs 35dB respectively (on max speed) I guess in the grand scheme of things a quieter fan, even if only by 8dB is probably worth it; what do you guys think?

Assuming those figures are correct, 8 dB is a lot! To hear the effect, fire up some pink noise through your monitors at a decent volume from your DAW or REW. Then reduce it by 8dB. Very noticeable - I'd easily pay ten times that amount for such a reduction!

Recall also that Gareth's build used 4 silencers in total, two on each leaf, so likely has a better fan noise reduction that you will get. This also points in the direction of the quieter fan.

You are of course correct. I'll go for the Rolls Royce Fan (more on this below with your additional posts)

Also, does this fan accept the speed controller (https://www.justfans.co.uk/speed-contro ... p-656.html - love the look of this bty, perfect for the soviet-style studio , Jennifer? I can't find that info...

I love the look of it too! No idea if it will be appropriate or not. The key is to get a variac controller. Normal dimmer type controllers will generate hum.

Great catch! I'll check this one with the company and if not, get a Variac one. Love the look of this though lol.

gullfo wrote:Source of the post to add some -- generally having the air entry on the "door side" but centered over the console or couch -- this makes any air vent or movement noise behave more symmetrical in the room. then the return (exhaust) farthest away. this will cause the (generally) correct air flow whether the room is fed from an open door (or window) or the supply. this is important because if you have a situation where doors are opened a lot or regularly, this can end up with air pockets of stale air. so a good cross-movement of air to remove co2 and distribute the oxygen is important. in large enough rooms i'll split the supplies and returns across multiple locations.

Good Shout Glenn! Something to take into consideration for sure.

endorka wrote:Source of the post Also, have you thought about an air filter? If you're going to use one it should be before the fan inlet to prevent dust & debris being drawn in to your studio.

I used an inline filter box like this and it was easy to install. After a while in use a significant amount of debris had accumulated on the filter itself, requiring replacement, so I'd say it was worth considering.

https://www.justfans.co.uk/duct-mounted ... -2946.html

Thank you! this look good. As I'm sure you're getting now, I'm not very clued-up on this stuff, haha. I will get one of these too! If there is anything else I may have missed, please chime in; I haven't had the time to research this properly recently, being so busy...

gullfo wrote:Source of the post another consideration (#moreExpensive) is an ERV unit to manage humidity and preserve energy (transfer temperature across inbound and outbound air), as well as a filter. basically a single unit which pushes fresh (relative thing if you're in an urban area) and pull stale air.
some info: https://www.ecohome.net/guides/2276/cho ... nd-an-erv/

Thanks Glenn, I'm in quite a rural area and not sure this is needed.

endorka wrote:Source of the post And yet another consideration before you commit to the fan would be estimating the static pressure of the entire system - grilles, ducts, silencers, filters etc. You can use this with the datasheet for the fan (linked below) to determine the likely air flow rate at different fan speeds.

If you'd like some help with this let me know and I'll post my workings here. Some static pressure values can be accurately derived from manufacturer test data for filters, grilles and duct. The silencers are trickier and based on estimates. IMHO is there is any doubt whatsoever that your chosen fan might not be up to the task, go for a more powerful model. You can always run it slower if it's over specified.

https://www.justfans.co.uk/pub/EN_TD-SILENT.pdf

Cheers,
Jennifer

thanks for this; As I said, there will very rarely be more than 2/3 people in the room at one time. I do want it comfortable for the odd time I may have the band in there (4 of us in total). Looking at the specs for the TD 500 (https://www.justfans.co.uk/silent-500150-p-1906.html) That you suggested, I was pretty happy with it. Do you think I should go more powerful?

Been trying to work out how much liner I need for these boxes and again it's not an easy calculation. Tom still has some liner left over that he is happy to sell me but I am looking into the logistics of shipping it. For now I think I need about 10 m of the 1200 mil wide by 25 mm thick liner.

I have a week off work next week so I'm going to try and get some stuff done on the studio in between days out with the kids.

Cheers, Sam.

#60

once the air is in the room, you can use flex duct in a ceiling soffit to route it. so if you don't want the cool supply air directly over your mix position (although if the air is moving slowly as it should -- it can mix with the equipment heat) you can route it to smaller vents on either side etc.

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