# Sound transmission in air returns



## lazerguy (Sep 28, 2007)

Hi guys,

We just moved in a new building with medical offices, and there is too much sound transmission between rooms. 

The walls and ceilings are OK, but the sound goes from one room to the next through the air return grids.

The suspended ceiling is the air return plenum, so we must have one air return grid in each room.

We tried locating the grids as best as we could, but there's still too much sound going through the grids.

Any idea if someone sells some special air return grid that blocks sound?

Thanks a lot!


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## SLSTech (Sep 13, 2008)

It has been years since I did commercial work - but this should not be happening. Each business should have its own AC unit(s) or fire dampers should be in use eliminating the noise transference

Are we talking only about inside your area & the med center is irrelevant? Maybe try a white noise generator or bring in an HVAC company


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## westernhvac (May 26, 2008)

*simple fix*

A couple of ways to attack this. Make a ductboard square back elbow to go over each return. These will just open into the ceiling space. Most times this will solve the problem. If ductboard is not ok then lined sheet metal els will work well also.


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## greghvacguy (Jan 3, 2009)

I have seen this. sounds like to me your ceiling is the return all open if you run duct work lined or duck board back from each office/room for 5 to 10 feet this will stop.


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## mdshunk (Mar 13, 2005)

Duct liner and flex to the final termination will both help.


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## flashheatingand (May 3, 2008)

From what I read, the problem is the whistling noise of air through the grids. In troubleshooting, I would remove one tile in each room that had a return grid to see if the noise ceased. If the noise ceased, the problem is not enough return air. 

How would adding flex lines or ducting stop this problem? I am not being critical, as I have been wrong many times and open to learn something new. Just inquisitive.


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## lazerguy (Sep 28, 2007)

Thanks guys.


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## izy (Jan 12, 2009)

*Return air boot*

Thermaflex makes a product for this application called a FlexaBoot that is designed to be installed on top of a 24x24 or a 24x12 return air grill. You can also rotated which way the flex is rotated to direct any sounds away from each other. The insulation in return air boots absorb sound and redirect it.


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