John Sayers' Recording Studio Design Forum Archive

I'm finding baffle boxes more and more baffling as I delve into them. I'd love to just type down my workings out and see where I'm going wrong as something isn't adding up for me. I recognise that this is going to be a long, arduous post but would really appreciate any advice on this as I've been stuck on baffle boxes for months now and every time I think I get somewhere I come across a new problem.

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Let's start with room dimensions I've added the area and volumes of the studio and the booth together labelled 'both rooms'. This is so I can calculate the size of a single baffle box on the outer skin feeding the air feed in of both the studio and the booth, and also have a box the same size with the air returns, again, being fed by both the studio and the booth.

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Working out baffle box sizes
Here are my workings out on how to find out the sizes needed based entirely on Gregwor's silencer box diagram (above) and this post by Gregwor: https://www.johnlsayers.com/phpBB2/view ... gn#p153517
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Problem
So based on those workings out, I need a baffle box to feed both rooms that has a 'Y' value of 27 inches. I've since discovered that I really need to make a baffle box with a 'Y' of 21.5 inches to fit between the studs. I reworked the formula to find the dimensions I need to create a Baffle Box with a 'Y' of 21.5 inches.
Ok. So I've found out the size of my baffle and discovered that the 'X' value is 7.25 inches. First issue, is that I need an 8in fan to feed my rooms as outlined in 'Step 2' above. Second issue is that this box ends up being smaller than the baffle for the studio, but bigger than the booth baffle:
Clearly this won't provide enough air flow to service both the studio and booth even if I have extended plenums within the rooms themselves.

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Solutions

I'm feeling that the solution here is to not combine the baffle boxes on the outer skin for both the studio and booth. This means punching 4 holes in the outer skin rather than 2, and have double the amount of outer skin baffle boxes - but if this is the solution, then that's what needs to be done.

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Questions
1. Are my calculations correct that these are the sizes I need for the rooms?
2. Am I correct that the solution is to create multiple baffle boxes on the outer skin to feed the rooms?
3. Am I ok with the outer skin baffle box feeding the studio being smaller than the one for the inner skin? The studio still requires a 'Y' of 25cms, so having an outer skin baffle with a 'Y' of 21.5 cms again doesn't seem enough. The fan itself needs to be 7in (18cms) to provide enough CFM to the studio so this feels tight.
4. I thought having a 20cm air gap between the studs was going to be loads, but squeezing a baffle box into this tight space seems very difficult (actual air gap is more, as it includes the depth of the studs themselves). How are people doing this with even less space than I have?

so back to basics:

1. room is 1200ft3 and you need a system to provide 6x per hour. so 7200ft3/hr = 120ft2/min = 2ft3/sec.
2. if you have a 1ft2 opening, you need to push through 2ft/sec velocity (120ft/min). these are good velocities.
3. can your system go that low? if not, perhaps some additional duct work and wrap-around cross-duct controls etc. to ensure that.
4. outdoor ventilation - 25%-35% of air needs to be refreshed. so a 50cfm HRV/ERV unit will do it.

so...

on the silencer question:
1. can you build a silencer that has a 1ft2 profile through out?
2. your in-room plenum - make it so it expands into say 2ft2 profile reducing the speed by roughly 1/2. distribute symmetrically in room. extract symmetrically same way larger plenum into smaller silencer.

this should avoid too many calculations and make it simple to build and install. the key is low system velocity.