Sound Suppression within HVAC Ducts

  • Thread starter Thread starter Jack Russell
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Jack Russell

Jack Russell

I smell home cookin!
I'm about to add HVAC ducts to my studio project. I'm nearby a furnace and AC unit, thus I want to limit the sound that travels through the duct to the studio, but keep the air flowing.

My HVAC supplier says that he knows about a new product that can be placed inside the ducts to help cut down the sound transfer. He is looking into it. I figured I'd post that here as well. Has anyone heard of such a material?

I did a search in here but am not finding what I'm looking for, unfortunately.
 
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BAFFLES
Here's a quote from Frederic a while back concerning ducts:

Whoever said there is more than one way to skin this... is correct.

If you have air ducts linking rooms to provide airflow (hot or cold), you can reduce the amount of audio going through them simply by making bends in the ductwork, putting in "traps" which are nothing more than metal boxes made out of the same material inline with the ductwork, full of foam. The foam will of course reduce some of the airflow, so you put the foam at the end of the duct right above (or below) the vent depending if its a floor or ceiling installation. I've done this before and it works fine. Make sure you can get at the box with the foam in it (use a hinged cover, etc) because the foam will become saturated with dirt, smoke, lint, dead bugs thus needing to be replaced every so often. If you can't figure out the foam block idea, you can put three staggered filters much like a muffers, and achieve similar results like so:

/\ /
airflow----> / \ / --- airflow -->
/ \/


Someone on this BBS posted pics of a baffle "box" one or two years ago. That might be what you are looking for. Your AC guy should be able to determine how much airflow restriction baffles would cause. This is very important because if you don't/can't move enough air you'll freeze up the evaporator.

DD
 
DigitalDon said:
BAFFLES
Here's a quote from Frederic a while back concerning ducts:

Whoever said there is more than one way to skin this... is correct.

If you have air ducts linking rooms to provide airflow (hot or cold), you can reduce the amount of audio going through them simply by making bends in the ductwork, putting in "traps" which are nothing more than metal boxes made out of the same material inline with the ductwork, full of foam. The foam will of course reduce some of the airflow, so you put the foam at the end of the duct right above (or below) the vent depending if its a floor or ceiling installation. I've done this before and it works fine. Make sure you can get at the box with the foam in it (use a hinged cover, etc) because the foam will become saturated with dirt, smoke, lint, dead bugs thus needing to be replaced every so often. If you can't figure out the foam block idea, you can put three staggered filters much like a muffers, and achieve similar results like so:

/\ /
airflow----> / \ / --- airflow -->
/ \/


Someone on this BBS posted pics of a baffle "box" one or two years ago. That might be what you are looking for. Your AC guy should be able to determine how much airflow restriction baffles would cause. This is very important because if you don't/can't move enough air you'll freeze up the evaporator.

DD
Click to expand...

Excellent. Thanks for the tip! I'll talk this over with the guy.
 
I'm no expert, but I've read on these forums that duct liner like the one you mention and Johns-Manville SuperDuct are very good solutions for quieting ducts. You also have to consider the distance, number of bends, and air velocity (whoosh).

I've used ordinary flex duct with a few bends and the sound absorption is very good, but the air flow is lousy. Flex duct is inefficient at transferring air and can easily crimp and obstruct the flow. Mine was used in a basement that had pretty good temperature control anyway so this didn't bother me much.
 
Update: Just talked with the HVAC guy. They supply a material that is essentially an identical duct shape that replaces all the metal in the duct. He calls it 'duct board'. So the whole duct will be constructed with this stuff without any special liner inside. He claims this will eliminate sound as well as anything. I'm going with it.

I think he knows what he's talking about because the owner of the company also has an in-home studio.
 
Jack Russell said:
Update: Just talked with the HVAC guy. They supply a material that is essentially an identical duct shape that replaces all the metal in the duct. He calls it 'duct board'. So the whole duct will be constructed with this stuff without any special liner inside. He claims this will eliminate sound as well as anything. I'm going with it.

I think he knows what he's talking about because the owner of the company also has an in-home studio.
Click to expand...

Duct board is basically highly compressed fiberglass. It is much quieter than metal, but you'll still probably want to design a baffle. This could be done with the duct board itself.
 
mshilarious said:
Duct board is basically highly compressed fiberglass. It is much quieter than metal, but you'll still probably want to design a baffle. This could be done with the duct board itself.
Click to expand...

With a good quality duct board (such as JM Super Duct) - making sure that the duct is sized large enough that you get the volume you need with out high velocity (and by this I mean I would like to see velocities kept below 100 fpm for a studio invironment) a single 90 degree turn will be enough to keep any noise from the system out of your room.

If your duct guy is going to provide a product different than the JM SD - make sure it is a polymer lined duct board. The polymer adds to the isolation and keeps the glass fibers from breaking free.

Sincerely,

ROd
 
Thanks for the suggestions, guys.

Of note: I told the guy that I regularly correspond with studio types on a forum. He said: "do what they say; I'm sure they'll know more them I!" :D

This place is a gold mine of information!
 
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