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Old 07-31-2011, 11:33 AM   #1
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Reducing A/c Pipe noise


I have the wall board down on my home theater and this has exposed the copper air conditioning pipes. The warm high pressure is not insultated and the cold low pressure is insulated with the usual rubber foam material. Now that the wall board is down the pipe noise from the compressor is very audible. I'm hoping to kill this sound before I put back the wall board to insure I do not hear it, though I didn't notice it much before the wall board was removed. I tried spray in foam insulation in the wall stud bay and this didn't help at all. In fact in may have gotten worse so I've carefully removed the foam to try something else. The pipe goes through outside brick siding, up the the 2 x 6 outside stud bay, through the top plate and through a 2 x 12 ceiling joist bay. I'm not sure which pipe is generating the buss noise as both are strapped together. Has anyone succeeded in killing this noise with isolation or insulation before putting up wall board?

Thanks for any help.

Keith

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Old 07-31-2011, 12:18 PM   #2
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Reducing A/c Pipe noise


check the condenser where that liquid line comes out might be picking up a vibration and travels down the LL to the evap inside....have somebody in the room as you move the pipes out side...is the condenser padded onto the concrete base if there...eye ball the compressor in the base of that condenser support rubber might of weathered and the base of the compressor is sending the messages along the pipe if that LL is wire tied to that insulated suction all the way into the air handler it has to be catching a rock or foundation or the condenser to send out harmonics acrosss the room..freon in the pipe will'nt produce it all of a sudden....

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Old 07-31-2011, 12:30 PM   #3
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Reducing A/c Pipe noise


If the noise is liquid sound from the pipe,
Insulation is not the way to fix this. The problem is caused by the pipe which may be blocked somewhere inside, or a sharp turn that narrows the passage of the pipe. By reducing/increasing the amount of freon may change the situation, but you need to make sure the level of charge is OK. If you know where the noise come from and they are not from compressor or evaporator coil,(some of the experienced AC tech can figure that out) replace that section may be the only way to fix it.

Last edited by clocert; 07-31-2011 at 12:36 PM.
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Old 07-31-2011, 02:18 PM   #4
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Reducing A/c Pipe noise


The condenser is mounted on a plastic footing sitting on the ground. Both the small, high pressure line and the cold low pressure lines are suspended in air and touch the house where they go through the brick siding (foam stuffing in the gaps). The complete unit is fairly new and in good working order.

Your questions prompted me to get my stethoscope and listen. When I put it on the insulated, cold, vapor line the buzz is loud. When on the high pressure, hot line there is not much sound but the contact area is very low (small line, larger flat stethoscope sound board). If I put the stethoscope on the face of a putty knife I hear the sound and it increases as I move the putty knife, in air, closer to both lines. I'm sure the buzz is normal compressor noise, transmitted down the pipes. As I indicated I didn't notice this noise before I took down the wall board in the room. It's now fairly pronounced within a few feet of the pipes. The pipes are not affixed to any part of the structure but mostly run through the stud and joist bay to the evaporator while hanging in air by their own stiffness. The high pressure and low pressure lines are tied together with tie wraps along there length. The structure contact points are 1) at the brick; at the wall; the top plate pass through to the ceiling joist bay; and at the evaporator. The rubber inslulated low pressure line touches the ceiling joist periodically with large single point clamps that do not compromise the insulation, but again it is not clamped tight to the structure.

What surprised me was after spray foaming insulation the sound got worst. I suspect the spray foam, though a good insulator and sealant provided a good sound connection between the pipes and the structure making it worst. I've now dug out the foam in the stud bay and am looking for an alternative. The putty knife experiment shows that where I’ve removed the foam the stud noise (stethoscope against wood) is low but still there. At the bottom of the stud bay where I’ve not yet removed all the foam the buss is much louder in the wood stud bearing out this theory that the foam is transmitting the sound.

Perhaps this noise will again disappear with new wall board, but a big part of this project is to sound deaden the home theater. So I'll feel much more confident if I deal with it before I put up the new wall board.

1) Questions does anyone know if this buss is primarily in the large cold line or the other?
2) Has anyone tried to deal with this buzz before simply installing wall board?
3) Obviously connecting the pipes to the structure with spray foam was bad idea has anyone tried something else?

Thanks Keith
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Old 07-31-2011, 03:05 PM   #5
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Reducing A/c Pipe noise


Are you talking about the normal compressor noise ? do you hear (you should) compressor noise in the room right next to the condenser unit ? Is your theater room far away from the condensor, but you still hear the noise ?
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Old 07-31-2011, 03:15 PM   #6
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Reducing A/c Pipe noise


The compressor is about three from the outside brick wall and the pipes go directly into the wall and go up the stud bay. And the noise is compressor operating noise or vibration. It sounds just like the outside compressor without the fan noise. Please note its its not obtrusive but this is a home theater and witiin a few feet of the pipes you can hear it.

Keith
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Old 07-31-2011, 03:38 PM   #7
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Reducing A/c Pipe noise


the suction is moving with the compressor pulling the gas back to itself the LL is the compressor pushing the Liquid to the evap/furnace i think the spray caused more sounding up then deadened...might of narrowed down the harmonics and your listening for it now might be psyc'g yourself out do you have surround sound neutralize it with the WOOFEERER

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