Author Topic: Soundproofing a Rooftop Centrifugal Exhaust Fan  (Read 1605 times)

kbarb

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Soundproofing a Rooftop Centrifugal Exhaust Fan
« on: February 19, 2015, 06:42:12 PM »
Hi,

This is the 3ft. diameter, round aluminum fan I'm talking about :

Rooftop Centrifugal Exhaust Fan

The problem is the fairly low frequency (?) sound of air rushing from the fan itself, that bothers the residential neighbors bordering the property. It's about like the sound you hear when you hold a large shell up to your ear at the beach, i.e., white noise.
The roof vibration is not a problem as the fan is well isolated.

I had an idea to build an 8ft. high cylinder and set it over the fan, about 1-1/2ft. below the top lip of the fan, and the rest above it. Then, line it with some kind of soundproofing material.

Is there a better approach, perhaps with baffles ? And, what would the materials list be.

I'll be building the project myself as I'm very experienced with building and quite proficient with tools.

Any advice would be greatly appreciated !

Thanks,

Kent

Randy S

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Re: Soundproofing a Rooftop Centrifugal Exhaust Fan
« Reply #1 on: February 19, 2015, 07:45:53 PM »
Ok Kent,

You are on the right track, go ahead with your plan however you need to give the sleeve a 90* turn and face it away from the neighbor.
Go ahead and line the sleeve with our SSP foam mat
http://www.supersoundproofingsales.com/SSP-Foam-Mat-3_8-thick-by-48-wide-with_PSA-per-foot/productinfo/09-42723-PSA/

You will need to modify the sleeve so that sound and air can not escape from the bottom.
seal it to the unit or roof deck.

Randy S.
760-752-3095
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

Randy S

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Re: Soundproofing a Rooftop Centrifugal Exhaust Fan
« Reply #2 on: February 19, 2015, 08:03:31 PM »
One more note:
at 1 / 90* we will get a reduction if we need more reduction we can add baffles after the 90* turn or add turns.
It will all depend on how much sound reduction you need to achieve with impeding the fan.

Randy S.
 
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

kbarb

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Re: Soundproofing a Rooftop Centrifugal Exhaust Fan
« Reply #3 on: March 03, 2015, 04:24:31 AM »
Thanks a lot for your advice and recommendation for the foam mat material. I'll figure out how much I need and order it.

I think a 90ยบ turn is probably going to be a bit difficult to fab but . . . what about something like this . . .

RoofFan - sound dampening hood_3

1. What materials should I make the cylinder out of ? what about sheet metal, and if so, should I spray it with a sound deadening compound ?  I think you sell one, no ? 

2. For the baffles - if I need them - should they overlap as in my diagram, so as to make a labyrinth type passageway for the air flow ?
About like I have it . . . more/less ?

3. I'm wondering if I can just leave the top open actually (although protecting the foam mat material from the rain and sun might be a good idea.)

I really appreciate your help ! !

-Kent


Randy S

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Re: Soundproofing a Rooftop Centrifugal Exhaust Fan
« Reply #4 on: March 03, 2015, 04:42:56 PM »
Kent,

Good job on the design! Pass!
You can do sheet metal and paint it with the dampening compound to prevent it from making noise as well.

Close the top leaving a 90* out the side of the tube and Yes for the baffles over lapping in your diagram this is exactly how you fabricate a baffle system.
Now remember that the more the 90*'s the greater the reduction however there is a limit on air flow...

Randy S.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040