Sound Dampening Panels on Ductwork?

Submitted by Casked_Away t3_yp9by9 in DIY

Hello DIY,

I have been searching for ways to reduce noise transfer from one part of my house to another that is coming through my HVAC ductwork. For example, we have our TV/movie area in our basement, but a movie, not even that loud, can be heard two floors up in a bedroom with an air return vent. Most of the things I have seen through Googling are just aimed at reducing the noise of the HVAC system itself, but that isn't my problem. Is there a way to insulate or perhaps use sound dampening panels on the outside of the ductwork in my basement ceiling to reduce the noise that is being carried up to the upstairs room? Would something have to be placed inside the ductwork instead? Or is there an easier way to handle this than what I am describing?

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Thanks in advance.

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systemdelete t1_ivib9wz wrote

In construction of studios we oversized the HVAC ducts to slow the air flow down and added internal alternating baffles lined with mass loaded vinyl which the air could wiggle around but knocked down sound transmission via the vents. / \ / \

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ShanghaiNick t1_ivi3wgj wrote

You would need to make an acoustic panel in your basement at least around the wall where the vent and duct is. You could use acoustic foam around the duct to prevent sound to some degree. But it sounds like you have a vent that is having sound transferred through it.

Since you cannot block the ventilation you will need to create barriers that prevent sound from entering closer to the sound source or at least a little ways away from the vent.

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drprofessional t1_ivi7ql3 wrote

You won’t be able to get rid of this 100%

Here’s what I did: removed drywall, filled every tiny hole with acoustic compound, and put in noise proofing insulation everywhere. I bought noise dampening blocks that you can attach to your ducts, but I’m not sure they do much.

Next, if I know I need quiet, I’ve put magnetic vent covers on the vent, which helped substantially. But, then you’d need to remember to take it off afterwards for proper airflow, and preventing carbon monoxide buildup…

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PerspectivePure2169 t1_ivi8dgw wrote

Nothing you put on the outside of the duct is going to help this, because the sound is traveling along the duct. The same as the speaking tubes they used to use on ships.

You may be able to cheat and absorb some sound with an air filter. Or if ducts are way oversized (as in plenum or joist chase returns) you could line them with acoustic board at openings. You may also be able to get noise blocking diffusers.

But mostly I think you're going to be stuck with this unless you remove and replace with duct board or similar.

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bandaidworld t1_ivjbk1w wrote

Spray some automotive undercoating or similar on the outside of ductwork. Same as they do for high-end dishwashers and under big metal sinks.

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Disarango t1_ivi4udh wrote

Use insulated foil ducting

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PerspectivePure2169 t1_ivi7k5t wrote

There's a big tradeoff with efficiency going this route.

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Maplelongjohn t1_ivlgxup wrote

There can be for poorly installed flex duct.

However properly installed,using even a short length of flex on each branch significantly reduces sound transmission.

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PerspectivePure2169 t1_ivmx0fr wrote

I'm just about as anti flex duct as they come, but I do think this is a reasonable way to do it. It uses it where it's strengths are. I used to do HVAC design and this was common and good practice there, from a properly sized branch system, with flex from the ends to the diffusers.

As the whole duct run, as is common in residential, it's no good. It falls into the realm of things that while theoretically possible to do well, just require a level of diligence and effort that aren't going to happen the vast majority of time.

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ntyperteasy t1_ivigbr0 wrote

Look for a product called "sound deadening duct liner" or "acoustic duct liner". Both are about 1" thick and meant to control vibrations traveling inside the duct. Adding mass loaded vinyl and securing the duct better will help with sound traveling in the duct metal. These people sell a lot of good choices - https://www.soundproofcow.com/soundproofing-101/how-to-soundproof-a-home-2/how-to-soundproof-hvac-systems/

I personally would avoid the open fiberglass duct board. It was (maybe is) widely used for a long time, but the fiberglass material is exposed on the inside and you invariably have to be introducing some fiberglass fibers into air circulation. There is no good way to clean it because it is friable and porous, and any vigorous rubbing will just release a bunch of fiberglass into your house...

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