sound proofing heating ducts problem - AVS Forum
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post #1 of 19 Old 12-29-2008, 09:45 AM - Thread Starter
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Hi,

We have a 2 storey home with a finished basement.

The basement room that we wish to watch movies in has a problem where by the sound travels through the metal heating/AC ducts of the house up into the 2nd floor bedrooms. The sound is definitely coming through the heat registers in the floors. We have 2 young children. If you put your ear to the duct you can hear conversations almost perfectly down in the basement "movie" room.

We would like to watch movies in the basement louder than we currently do on the first floor. Because of the way the ducts are working, sound in the basement carries up into the 2nd floor bedrooms louder/worse than the first floor. However we can't use the bass much at all. The potential for the basement movie viewing is greater than the 1st floor if we can just solve the ducts problem.


I've done some research and know that we could line the duct pipes with sound proofing insulation. But I don't believe that is the root cause. Root cause is sound entering the heating registers in the cieling of the basement acting as conduits to the rest of the house, which explains why 1st floor sound is more quiet than basement sound reaching the 2nd floor.

there are baffle boxes and sound baffles? Are these for insertion into the ducts? Where can they be bought?

any advice would be greatly appreciated. I've called some custom sound installation "expert" installers/contractors in my town who do home theatre builds and they know nothing.

Thanks

haggisns
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post #2 of 19 Old 12-29-2008, 10:44 AM
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First off, lining ducts with duct liner reduces the ability of the duct to transmit sound down the length of the pipe. Sound entering at a register has a tougher time making to the other end, if you have some bends even better.

Do you have access to the ductwork in the ceiling of the basement? If so you might think about putting in some acoustical ducts instead of your pipes.

see product 6M on the flexmaster.com web site.

Also, they do sell in-line duct mufflers which attacks the problem the same way by inserting a section of pipe that is lined with acoustically absorbent material. Google will get you some vendors.

here is one:
http://www.suncourt.com/DuctMuffler.html
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post #3 of 19 Old 12-29-2008, 11:43 AM
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I'd get some dynamat. They sell "hoodliner" for cars that would work perfect inside the ducts right where the sound is entering your ductwork.

I just finished my basement and I put dynamat extreme all over my duct work, as it would "boom" when the furnace kicked on. Now, my whole furnace is silent. The only way you know it is on is my walking by a duct and feeling it!

I plan on buying some dynabox's for my in ceiling speakers next... The bass from mine is super loud upstairs. Those force the sound into the theater and eliminate it from anywhere else, also increasing your speakers effeciency and power capacity... Plus you can install them even when your room is already done!
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post #4 of 19 Old 12-29-2008, 02:23 PM
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Use duct liner to line ducts to reduce longitudinal sound transmission...Linacoustic RC.

Use Dynamat to dampen noise caused by vibrating sheet metal.

And Free FYI, I just ordered some Dynamat Extreme this weekend to tame my furnace. I hope you are right.
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post #5 of 19 Old 12-31-2008, 06:47 AM - Thread Starter
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Thanks everyone for the reply.

I was hoping I could insert something into a duct, but if required I do have access to the duct work in the basement cieling and will think about acquiring the duct mufflers.
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post #6 of 19 Old 12-31-2008, 06:54 AM
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If you have access IMHO replacing a section of the duct with true acoustical duct will be a cheaper and probably have a better effect compared to the duct mufflers.

I have no scientific evidence to back MHO it just seems that a 10 ft length of acoustical duct is better than a 3 ft length of muffler.

If you can add some bends even better.
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post #7 of 19 Old 12-31-2008, 08:07 AM
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Quote:
Originally Posted by BIGmouthinDC View Post

Use duct liner to line ducts to reduce longitudinal sound transmission...Linacoustic RC.

Use Dynamat to dampen noise caused by vibrating sheet metal.

And Free FYI, I just ordered some Dynamat Extreme this weekend to tame my furnace. I hope you are right.

I couldn't believe the difference...

Even my wife noticed!

Plus, I had a duct under the floor in my bedroom. And every time I stepped on it, it would make a noise...

I threw some extreme on the bottom of the duct, where it was easy to reach from below, and it fixed it! No more noise.
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post #8 of 19 Old 12-31-2008, 09:11 AM
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My box of extreme arrived yesterday. I took some db sound readings of the before, I will start a thread documenting the results in 2009.
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post #9 of 19 Old 12-31-2008, 11:39 AM
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Quote:
Originally Posted by BIGmouthinDC View Post

My box of extreme arrived yesterday. I took some db sound readings of the before, I will start a thread documenting the results in 2009.

I'd be very interested in your findings.
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post #10 of 19 Old 01-02-2009, 10:00 AM
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How much of the Dynamat Extreme do you need to place on the duct to be effective? I assume you don't have to cover every inch of the duct. Where did you place it? Just near the registers? On the furnace?
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post #11 of 19 Old 01-02-2009, 04:06 PM
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I went way overboard on mine... You don't need much. Once I realized this, I started cutting it into strips, and then tapping on the cold air return, and ductwork, and when it was loud (vibrating and booming) I would put it on. I've put enough on there so that I can tap it all over, and it sounds like wood instead of sheet metal.
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post #12 of 19 Old 01-02-2009, 04:30 PM
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Quote:
Originally Posted by Tom Bley View Post

I'd be very interested in your findings.


Just a preview, disappointing in my particular situation. As it turns out most of the noise from my gas powered furnace is the burner noise that radiates out of the open air vents which of course can not be covered. If your noise is the rumble of the fan transmitted by the sheet metal then it may prove useful. More results, pictures and measurements to follow after I complete all the remediation steps I'm planning.

If you have one of the newer higher efficiency furnaces from my experience they are much quieter and the fan rumble is the most noticeable sound. I have one in the attic and I've been kind of waiting for the unit in the basement to fail.
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post #13 of 19 Old 01-05-2009, 01:02 PM
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Quote:
Originally Posted by BIGmouthinDC View Post

Just a preview, disappointing in my particular situation. As it turns out most of the noise from my gas powered furnace is the burner noise that radiates out of the open air vents which of course can not be covered. If your noise is the rumble of the fan transmitted by the sheet metal then it may prove useful. More results, pictures and measurements to follow after I complete all the remediation steps I'm planning.

If you have one of the newer higher efficiency furnaces from my experience they are much quieter and the fan rumble is the most noticeable sound. I have one in the attic and I've been kind of waiting for the unit in the basement to fail.

Thanks. I'm going to try it because mine pings when it kicks on and off in areas. Even after the heat shuts off for a few minutes I get a bunch of pinging noises.
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post #14 of 19 Old 01-05-2009, 01:09 PM
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Quote:
Originally Posted by Tom Bley View Post

Thanks. I'm going to try it because mine pings when it kicks on and off in areas. Even after the heat shuts off for a few minutes I get a bunch of pinging noises.

IMHO if applied to the section of the duct that is pinging you should have some improvement.
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post #15 of 19 Old 02-16-2009, 04:34 PM
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This is probably a silly question but did you put the dynamat INSIDE the ducts or wrap the outside... Im assuming inside Im just hoping Im wrong as I have no clue how to disassemble and reassemble ductwork
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post #16 of 19 Old 02-18-2009, 07:16 AM
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I would assume that the extreme is installed externally to the duct as I doubt that it's rated for in-duct applications. The Dynamat website shows it being installed on the outside of pipes, ducts, dishwashers, etc.

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post #17 of 19 Old 09-22-2013, 11:38 PM
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How did you make out with your duct noise problem? Curious since we have the same issue.

Thanks
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post #18 of 19 Old 09-22-2013, 11:42 PM
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Quote:
Originally Posted by BIGmouthinDC View Post

First off, lining ducts with duct liner reduces the ability of the duct to transmit sound down the length of the pipe. Sound entering at a register has a tougher time making to the other end, if you have some bends even better.


Do you have access to the ductwork in the ceiling of the basement? If so you might think about putting in some acoustical ducts instead of your pipes.


see product 6M on the flexmaster.com web site.


Also, they do sell in-line duct mufflers which attacks the problem the same way by inserting a section of pipe that is lined with acoustically absorbent material. Google will get you some vendors.


here is one:
http://www.suncourt.com/DuctMuffler.html


It's been a while since you suggested the 6M by flexmasterUSA - is this still the acoustical flex duct of your choice or have better products come out since then? What have you worked with?

Thanks
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post #19 of 19 Old 09-27-2013, 11:07 AM
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hi! I've got a somewhat similar issue...looking at buying a new house...there's an upper main floor, a middle floor with master bedroom, and then lower basement level...all three floors have a large cold return vent connecting them like a column in the center of the house..
...I'd like to have a piano on the upper floor, and rent out the lower basement...however, one major problem right now is, I turned on my ipod on the upper floor, not even at a loud volume and down in the basement you can hear it almost as if you are right next to the ipod...you
can hear people's conversations clearly as well...
...i'm thinking about sealing off the basement cold return and closing all vents, and installing a ductless heat pump for heating down there....what do you guys think of this, and how would you suggest to deal with the sound travelling issue? welcome all suggestions!


Thanks!
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