ventilating an iso booth......ssssshhhhh

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erichenryus

erichenryus

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anyone have any DIY tricks for silencing ventilation ducts for a homebuilt iso booth?

i'm about to start on this project but there's this last detail of breathing and not allowing noise from the outside getting in through the ducts.

i checked around on the web and there's a company called fantech that sells silencing kits but i'm wondering if anyone knows any DIY tricks that achieve the same result using common ducting and inline fans from Home Depot.
 
You could do what Whisper Room does - use a small squirrel cage type fan (quieter than axial flow types) and build an S-shaped duct with about 4 feet run, reverse direction, 4 feet, reverse again, so that there is no straight path from inside to outside - line at least the inside corners of this S-shaped duct with foam and rubber mount the squirrel cage fan for vibration. You might need to build two such ducts on opposite sides of the booth, one for outflow... Steve
 
erichenryus said:
thanks steve.

what's a squirrel cage fan?
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It's like a hampster cage with a wheel in it - you put a squirrel in it, and when he runs on the wheel it turns the fan. The only method that is quieter is to use a gerbil cage fan. :D

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OK, surprisingly enough all the jokes were close to a REAL explanation -

An AXIAL fan is one like your typical window fan - the air flows on the same AXIS as the fan blade spins.

A squirrel cage fan is called that, because it really DOES look like a hamster wheel. Picture a small water wheel inside a shroud, with an air opening into the center of the wheel. the buckets, instead of being solid, are louvers. These louvers (slots) are shaped so that they push a little bit of the air in the center of the wheel out a spout on the shroud's outer perimeter. There are dozens of these little louvers, each one putting a small amount of air out the spout, so no single louver causes a drastic disturbance in the air. End result: more air, less noise.

Picture be worth 1000 words...

http://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId=1611630888

There are sizes of this type of centrifugal blower from very tiny, to several FEET in diameter. One for a vocal booth would be about the size of the one in the link, or maybe a little larger... Steve
 
Actually, for a vocal booth I'd use this one

http://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId=1611630892

I'd cut a 4x12 hole thru the upper wall, build a plywood duct about 6x12, and mount the dual blower blowing horizontally into the duct, which would turn 90 degrees, go up the outside wall, turn 90 degrees, go thru the wall, turn 90 degrees and go to near the bottom of the wall, and vent into the booth. This would give you 3 90 degree turns, put foam on all inner surfaces of the duct, and you should get enough air with good isolation.

The blower in this link has flanges on the air outlets, which should be mounted with neoprene to minimise vibration. Maybe another neoprene pad under the housing to take the strain off the flange mount, so the rubber isn't compressed as much.

If the blower is still too loud, you can use a plug-in speed control like this one

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=43584

to slow the fan down. Moving air generates noise that is roughly proportional to the 4th POWER of velocity, so a small reduction in air speed would get you a large reduction in air noise.

By having the outlet of the duct near the floor, you would lessen the amount of air noise getting into mics, especially for vocals.

Hope this helps some... Steve
 
Thanks so much Steve. Never seen one of those before, and you certainly can't buy that at Home Depot!

I framed my booth this weekend and I'm close to this part of the process so this is very timely! I'll build the ducts into the frame so I can drywall over them.

I have a really stupid question though. Can you reverse the direction of the airflow on those things? So for the air going OUT of the vocal booth can I do everything the same way with the fan mounted flush to the outside wall of the booth and just reverse the rotation of the fan?
 
Save your money, and just build the same kind of duct (without a fan), but with multiple right angles and foam, for sound attenuation. Unless you plug up the hole, whatever you pump into the booth must go out.

This has the added advantage of giving a slight positive pressure in the booth, so when you open the door any dust will go OUT instead of being sucked in.

I.m not positive, but I think that shaded pole motors are NOT reversible. For that, you need either a DC motor or a 3-phase, neither of which is practical for most applications...

If I were doing it, I'd put the outlet at the TOP of the booth (inside), and run the duct down the inside, thru the wall, and back up to the top to another 90 degree, so that the HOT air will be the first to exhaust.

And remember to use non-hardening, either silicone or Butyle caulk on EVERY joint. You want everything hermetically sealed, and preferably double-walled for isolation... Steve
 
I cannot thank you enough for all of that info knightfly! I really was tripping over how to ventilate this thing.

If you need any vocal or drum tracks in the future let me know.

I'll post pics for all when I'm done.
 
Cool, glad I could help - The booths from WhisperRoom are pretty neat, but they want around $6 to $10 THOUSAND for one with double walls and a vent kit - you can save enough by building your own to pay for a SERIOUS piece of gear for the studio... Steve
 
That's exactly why I'm building this! I was looking into a 4X6 room from soundsuckers.com but it was 3500 when the shipping was figured in! Then I thought....hmmmmm with the extra 3 grand I'll have after sweating it out I could buy a serious microphone.

I'm photodocumenting the whole process so I'll post pics when I'm done. I mean if I can do this......anyone can!
 
Wow, I actually have 3 of those squirrel fans stored in my barn. My sound man gave them to me. I haven't found a use for them yet. Cool. unless someone wants to make me an offer. of course i'm planning a vocal/amp room beside my control room, I guess i should keep em. Thanks for the tip.

Terry
 
knightfly, wanted to let you know that i just got that fan (the second one you mentioned) and that sucker is LOUD! I'm gonna try the voltage dial you referred to cause at lower speeds it seems pretty tolerable but when it revs up it's like an airplane. Louder than my furnace actually. I'll tell you what though, it moves a LOT of air so I definitely won't suffocate in there. :).
 
If you want quiet, get a Trane XV80 Variable Speed furnace. I can't even tell mine is on (which is sometimes a bad thing). Of course, this may be over your budget.

Also, if you want an idea of just how quiet they are, you can literally be standing directly in front of one and not even know it is operating. Unless you have completely bogus ductwork (as in a state of needing repair, or very poor design), this is a great option.
 
Interestingly enough I just bought a Trane XV-90 last winter and you can tell when it's on! So that upgrade has already happened and I'm not buying a new furnance ever hopefully. but it is still quieter than this squirrel cage fan....for now. I'm gonna try lowering the voltage on this thing and see what that does.

come to think of it.....maybe i should just be tapping into the existing ducts since the thing runs constantly? hmmmmm.
 
Hows your ductwork? I have been up to an XV90 and Xv80 at full speed (2nd Stage), and it is VERY tough to hear. And if you have the proper diffusers at the end of a good ductwork line, you simply cannot hear it....

Where I work we sell a ton of these things, people call all the time complaining that the furnace is "broke".....lol

BTW - If you are going to lowering voltage on that XV90, you may run into problems. That is a DC motor, not AC. There is a board inside the case that converts the voltage. Plus that is a ramping "intelligent" motor. It will run at speeds necessary to deliver the proper CFM.

However, there is a board in there also that contains a set of dip switches. The settings on these switches dictate to the motor optimal or "run" settings. You could try tweaking those for a better result. If you need info on those let me know (I happen to work for Trane, trying to NOT let this be an ad). Perhaps these switches were not set optimally at installation time???

- RichHead
 
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erichenryus said:

come to think of it.....maybe i should just be tapping into the existing ducts since the thing runs constantly? hmmmmm.
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Yes, all Trane's with the variable speed are designed to cycle as little as possible. Because they cost so little to run, and are reliable, its not a huge deal. I would tap off of there actually the the straightest run possible. Hard bends in ductwork can actually cause turbulence too, insulated or not. Unless they are, of course, very well built ducts.
 
rich, it's a 75 year old house that i'm sure was retrofitted for ducts so i'm sure the ducts aren't optimally layed out. But then again I don't know the first thing about ducts. But I'm about to find out! There's a freaking vent that's never open right next to my booth! Duh! I've been fucking around with squirrel fans and such and I can just tap the main trunk! Anyone wanna buy a 'Dayton shaded pole blower' ?
 
erichenryus said:
rich, it's a 75 year old house that i'm sure was retrofitted for ducts so i'm sure the ducts aren't optimally layed out. But then again I don't know the first thing about ducts. But I'm about to find out! There's a freaking vent that's never open right next to my booth! Duh!
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lol...right on man. Go get 'em. Well, if you were in las vegas I would know exactly which sheet metal shop to point you to. If you want somebody to build ducts for you (or even design them), call a local HVAC contractor and ask who does their metal work. you could save some cost by installing them yourself. Either way bro, good luck....wish I had your setup (even with the old house).
 
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