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Who has solved the HVAC air noise problem?

I am in the redesign stage of a totally dedicated listening room which will inlcude tube amp, pre-amp and cd player. The reconstruction will include a flat ceiling and tons of sound isolation and insulation. The central air system for the house with constant air flow produces way too much background noise and hum through the vents. I want to add a separate dedicated a/c system for just this room (25Lx15W x 9.5H). I am looking for the advice of those who have managed to baffle internally in the ducts sufficiently to eliminate the air flow noise and machine hum, while still having an effective a/c system. I want an invisable a/c system with five overhead vents. Duct size should not be a problem as the walls will be at least 12" thick at one end. I presume that fiberglass or lined/insulated sheet metal with all surfaces covered are the way to go. BUT, I really don't know. What I know is that I want to be able to never hear the environment, only the music.

All thoughts welcome including my obvious need for more therapy.

Bill E.
lakefrontroad
dweller's avatar
dweller
3,781 posts
 
Installing staggered baffles inside of your vents will help. This means extending a padded piece of plywood, or whatever, halfway into the duct then doing the same on the opposite side a foot or so further along. four flanges should do it. Also, flare the air exit so the register is (3 or 4 times) bigger than the main shaft. This slows down the air-stream and associated noise. Consult a pro for the nitty gritty...
lakefrontroad OP
302 posts
 
Dweller,

I've done very similar baffling in hvac systems in a prior home to reduce air noise. The staggered baffles were metal disks with the centers cut out which slowed down the air in line ahead of the vents by a few feet. It reduced the noise enough that I could tolerate being in the room, but I wasn't looking for zero noise and can't remember how quiet it was.

Your solution sounds more effective. As to the flaring, it makes sense to me. I can't imagine that the loss of back pressure to the vents would have any effect since I'm only trying to balance one rooms vents.

Is there an excellent solution for dust management?

Best wishes,

Bill E.
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jeff_s
20 posts
 
Why not just turn the HVAC system off when you are doing critical listening?
artemus_5's avatar
artemus_5
1,927 posts
 
The biggest reason for a noisey HVAC system is generally a poor return system. Many will try to use 1 return air duct which is centrally located in the house. The better alternative is to put 2 in and try to keep them in hallways if possible. This is the way I did my house and I cannot tell when it is running. Another problem may be an air handler too big for the system.
If you use a separate system you will have to put a return air duct in the room which is not desireable. A better alternative is to increase the size of the existing system (heat pump I pressume) and install another return air duct. An experienced HVAC contractor should be able to remedy this noise problem for you. Also DO NOT use duct board unless you like breathing in fiberglass particles. You probably cannot find it anyway. I haven't seen it used for years and it is probably against code also. Metal trunk lines with flex duct is the way. Trunk lines should be wrapped with insulation. HVAC should not be noisey. Good luck
karls
332 posts
 
Several things:
1. not all blowers are created equal; shop around.
2. keep the blower as far from the room as possible.
3. make the ducts as big as possible; the drop in noise from doubling the size of the duct will astonish you and is probably more effective than anything else you can do. I cannot emphasize this enough.
4. Mechanically decouple the ducting from the pump/blower unit with a flexible coupling to eliminate vibration transmission.

There is tons of good info in F. Alton Everest's Master Handbook of Acoustics, around $40 in paperback. It is well worth getting a copy before you really start planning.
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