HVAC vents (registers) are killing my sound

  • Thread starter Thread starter rothy
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rothy

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Hello all - I am looking for your wisdom yet again...

I am setting up a new studio in my home and am having trouble silencing the A/C vents supplying cold air to the room. I live in Phoenix, AZ and simply turning off the A/C would not be an option... the A/C runs even when the thermostat is set at 78 - I even have a high-efficeincy Trane package heat pump - but it's 120 flippin' degrees outside.

I am just looking for low-cost DIY solutions, as I am not ready to build a room within a room or construct an iso booth. My room is about 20'x20', and there is one 20"x20" return air (sucking vent) and 2 12"x12" registers (blowing vents). All vents are in the ceiling, one of which is directly above my recording/mixing space. The room is also very well insulated and isolated from the rest of the house - this means no outside noise is getting in, but when I close the door to the room, it creates a very "tight" space, and the vents blow even harder. I have also installed some corner traps and other wall treatments - no egg crates.

My first idea is to create a box from acoustics foam (13"x13"x6") that can be placed over the vents, attaching to the ceiling with velcro. I would place holes on the sides that would still allow air to flow, just directed up/sideways instead of right DOWN into my mics. I won't know if this works until I try it I guess.

Has anyone else had this problem, or been able to overcome this with a specialty vent or something?

Thanks!!
 
Item one; is the vent noise level ok until you close the door? If the supplies and returns (the total system) are sized well, the flow should not be changing. (Although I'm having trouble guessing why the flow would go up closing the door.. unless the return path for that room is restricted.)
Second, if part of the problem is the air hitting the mics (rumble?) the guides might help that. But if they are open to airflow they might only cut some of the high freq noise.
Wayne

edit add on; Also, the quietest (normal type) vents are the ones that are the most 'open' and have the least amount of small parts. Also consider removing the grills completely.
 
mixsit said:
is the vent noise level ok until you close the door?
Click to expand...

No, it is still way too noisy even with the door open.

mixsit said:
If the supplies and returns (the total system) are sized well, the flow should not be changing. (Although I'm having trouble guessing why the flow would go up closing the door.. unless the return path for that room is restricted.)
Click to expand...

I am 100% positive the system is sized right. I work for an HVAC sales/marketing training company, and had complete control over entire installation. This room is a converted garage, and I think it is simply too tight of a room. I have 18" between me and the amin house (brick, plaster, drywall and insulation). The rest of the house is very open.

mixsit said:
If the supplies and returns (the total system) are sized well, the flow should not be changing. (Although I'm having trouble guessing why the flow would go up closing the door.. unless the return path for that room is restricted.)
Click to expand...

I am 100% positive the system is sized right. I work for an HVAC sales/marketing training company, and had complete control over entire installation. This room is a converted garage, and I think it is simply too tight of a room. I have 18" between me and the main house (brick, plaster, drywall and insulation). The rest of the house is very open.

mixsit said:
Second, if part of the problem is the air hitting the mics (rumble?) the guides might help that. But if they are open to airflow they might only cut some of the high freq noise.
Click to expand...

No air hitting mics directly.

mixsit said:
Also, the quietest (normal type) vents are the ones that are the most 'open' and have the least amount of small parts. Also consider removing the grills completely.
Click to expand...

I have removed the grills completely... to test it. There is a lot less noise. Though still audible on my recordings.

Thanks for the help, we are making progress. :)
 
I built a sound absorbing box on my A/C vent using 3/4" plywood, 2x2 lumber, lots of caulk, and 1" thick rigid fiberglass insulation (Owens Corning 703) wrapped in cloth. I don't have any A/C noise at all to speak of. The big thing that I think helped was that the output is at 90 degrees compared to the input of the absorbing box. There are some pictures of what I built here: http://www.gracesongmusic.com/studio_c_2.htm

-lee-
 
you want diy, baby, here is diy............

rothy said:
No, it is still way too noisy even with the door open.



I am 100% positive the system is sized right. I work for an HVAC sales/marketing training company, and had complete control over entire installation. This room is a converted garage, and I think it is simply too tight of a room. I have 18" between me and the amin house (brick, plaster, drywall and insulation). The rest of the house is very open.



I am 100% positive the system is sized right. I work for an HVAC sales/marketing training company, and had complete control over entire installation. This room is a converted garage, and I think it is simply too tight of a room. I have 18" between me and the main house (brick, plaster, drywall and insulation). The rest of the house is very open.



No air hitting mics directly.



I have removed the grills completely... to test it. There is a lot less noise. Though still audible on my recordings.

Thanks for the help, we are making progress. :)
Click to expand...



absolutly remove the grills, get about 20 feet of 18" flexiduct (insulated r5 will do. totally duct tape it over the outlets with NO leaks, put at least one 90 degree curve or better an s curve. run them bother over ot opposite where you record, at least 3 feet from the wall. do the same with the return vent, but take to to the middle of the room.

you want the air to kind of tumble out, not be pushed out, no grills, no obstructions.
 
rothy,

as much as you might want to believe that the system is set up correctly - it isn't.

It might be fine for standard home system - although I am very puzzled why you have only have 288 square inches of supply into this room yet you have 400 square inches of return - but the fact of the matter is that your velocity is too high.

For quiet HVAC in a studio = you need high volume with low velocity.

If you want to quiet it down the 1st thing you need to do is add more supply line (off the same trunk) to maintain the volume while you decrease the velocity in each trunk.

I wouldn't have much more then 250 to 300 fpm - I would guess (just from your description) that you're over 800fpm.

In a perfect world I wouldn't exceed 100fpm - but that gets fairly expensive.

Rod
 
Rod Gervais said:
I am very puzzled why you have only have 288 square inches of supply into this room yet you have 400 square inches of return
Click to expand...

I forgot to mention that the 20'x20' room also includes a bathroom (with another 6"x6" register) and a sectioned off closet (about 6'x4'). With these taken out, the actual room becomes about 13'x20'.

Not sure if any of that matters... but it would make sense that adding another register would reduce flow rate, while maintaining same volume. That is probably the best bet.
 
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