Ventilation for a small Audio Booth!

[Karlz]

Hi there, hoping to find some much needed help!
Have made a Audio Booth for voice overs, inside a room, inside a wooden house, inside a rain forest.
Its pretty much looking like a retro phone booth as its only 2.400m long x 1.200m wide, and not knowing anything about building, its, lets say...got a lot of character!!
Its heating up here in the tropics & ventilation is a must.
Please refer to diagram: Studio room is next to bedroom & the current unadvised plan is to put the quietest of nexus 140m or Noctua 200m computer fan at the bottom of the wall of the adjoining room next door, (bedroom), so it can pull in the cool air-conditioning from that room in through that fan, where behind it, in the studio room it will be attached to a baffle box under a bed, which will be attached to some duct that I'll cover in acoustic insulation & tape that will curl its way around to the bottom of the booth where it will find a hole running onto the booth.
I will have the computer & interface on a table outside the booth.
But whatever computer fan I choose, they all talk about 3-4 points for connection, when I just want to plug it in via a usb electrical outlet that is in the bedroom right near where the fan would go.
Is there a way to do this, as it wont be connectered to computer?
And if so, would this plan work?
If not, would be most happy to hear one that would!
Thank-you for your time
Karlz

[Gregwor]

Do the math to calculate the CFM/Tons to provide 6 air changes in your booth per hour. Make sure your AHU and duct size permits that flow. Flex duct has a lot of downsides in that it causes a lot of friction loss. Try to avoid it and if you do use it, use it in as short of lengths as possible and use oversized. Typically you want 4 silencers, not one. You typically want one of each leaf, and for both supply and return. To get quiet air flow, make sure your air velocity is equal to or slower than 300 feet per minute. That often means large ducts/registers. For your supply, you'll want your inner leaf silencer to be at least twice the cross sectional area of your supply duct (the one that you calculated you need to provide the correct CFM for your room. It may need to be even larger to achieve the 300FPM air velocity. Or, if your silencer cannot be mounted directly to your inner leaf, you can run duct from it's outlet throughout your booth to hit a register. But, that duct will have to be large enough to get your CFM low enough. Don't try to use smaller duct and have a large register because all of that turbulence and change will create noise. Do it upstream.

For your returns, do all of this backwards.

IF you make sure all of these parameters are met, you'll have an excellent booth (temperature-wise).

If you need some equations to sort this out, let us know. They are scattered throughout the forum though. You can even find them with a quick google search.

Greg

[Karlz]

Thank you Greg for all that great info. Now i hve something better to jump off into the land of the vents from.
Muck appreciated!

[Gregwor]

Awesome. I thought I'd just post these for you to save you the hassle of finding them:

Cubic Feet per Minute (CFM) = [# of air changes per hour multiplied by the volume of your room (in cubic feet)] divided by 60 minutes.

example: a 1000 cubic foot room would equate to:

[6 air changes X 1000 cubic feet]/60 min = 100 CFM

Cross Sectional Area (in square feet) = CFM divided by air velocity (in feet per minute)

example with the 100 CFM from the example above:

100 CFM / 300 feet per minute = 0.33333333 square feet

To convert that into square inches, you just multiply your square feet by 144.

So, 0.33333333 square feet X 144 = 48 square inches.

What that means is, your furnace/air conditioner needs to supply your room with 100 CFM. Looking at online charts, or using an online ductulator, you will see that a 6" round duct will supply 100 CFM. I'm not calculating friction loss because our runs are probably going to be pretty short AND we are going to have an extra fan on the return duct to help move air along through the silencer box. Plus I'm not that smart with this stuff.

Therefore, the inlet of your silencer box will be a 6" round duct.

A 6" round duct has the cross sectional area of:

π r squared = π X 3 squared = 28.27 square inches

The inside of your box has to be at least double that. You can divide up that 56.55 square inches in any rectangular division you want.... let's just say 5.5" X 10". Your silencer has to have 1" of duct liner in it and must be made out of material that equals the surface density of your walls. An inch of OSB is probably a good starting material (which should equal a bit more surface density that two sheets of 5/8" drywall).

Leaving that box should either maintain that cross sectional area or get bigger depending on what speed we are achieving with that 56.55 square inches. We already calculated that with 100 CFM of air at the maximum allowed air velocity of 300 feet per minute, we would require a cross sectional area of 48 square inches, so we are good to go maintaining that 56.55 square inches. You could either use a 1" thick OSB sleeve to penetrate your inner leaf, or connect that to a lined duct (probably need a 6" x 10" interior dimension. Add 1" of duct liner and you'll be sitting at an 8" x 12" rectangular duct. Run that to a register where it's cross sectional area matches your 56.55 square inches or bigger.

If you're curious what your air velocity would be with the 56.55 square inches, just rearrange the formula and come up with:

air velocity = CFM divided by the CSA

So, 100 CFM divided by (56.55 square inches divided by 144 to make square feet) = 100 CFM divided by 0.39269908 square feet = 254.65 feet per minute. That's pretty awesome.

I'm self taught so hopefully I didn't screw any of that up, if I did, I sure hope someone corrects me because I'm designing my place using these calculations!! If I am correct, I hope this saves you some time and maybe someone else too.

Cheers!

Greg

[Karlz]

Wow! Thanks so much Greg, very much appreciate your input & time.
This side of this business is a nightmare for getting information in this isolated place.

Am still at a loss at what kind of fan to get that can connect to electricity outlet or a USB outlet on the electrical board.
I called up Noctua to ask if there is a way I could change the connection for their computer fan Noctua NF-A20 FLX 200mm & they said they could not advice usage of their product if intension was to be used in another way than what it was intended & would loose my warrenty!
Then I saw on u-tube 2 vids of people doing just that! They connected a smaller computer fan using a plug in transformer! It looked very simple but a little concerned Ill set my house on fire!
The particular Noctua fan i think i want has Max Input Currant- 0.08A.

Thanks again.