best way to dampen exhaust 'woosh' sound?

[Shliite]

High everybody - thanks for stopping in. As usual any input and discussion are welcome.

The title pretty much says it all. I have a 150 inline can fan pulling through an odor sock and pushing through a 400w hood then right to the exit. A 4" flex duct runs through the entire system and exits through the closet door (made of plywood). I've added 2" foam boards to the doors to dampen sound from inside the closet, but still the noise from the exhaust hole is overly noticeable for my worries to be at ease.

so.. for a little visual help thats:

Odor Sock ---> 150cfm can fan ---> 400w enclosed hood ---> closet door
- 4" flex-ducting
- ~90 cf closet
- (2) 4" passive intakes

I've considered wrapping the last 2 feet (give or take) of flex duct with that fiberglass insulation wrapping material you see at the hardware stores (i think its supposed to be used for water pipes etc.)

I've also considered widening the last foot or two to some 6" flex duct and trying to pack some poly-fill cotton batting around the edges - thus leaving a 4" cylinder for the air to pass through. I cant think of a good material to form the inner cylinder. Perhaps just leaving the 4" duct and putting the 6" over it. ...but then that would pretty much just be the same as idea #1...
sorry just thinking out loud.

And lastly I've considered putting some sort of breathable sound dampening material over the exhaust hole... or packing it about 1/4 - 1/2" thick at the end of the flex duct (so it is internal rather than external). I wouldnt want to use anything that would constrict too much airflow though.

anyways... if your asking yourself why i haven't tried any of these ideas yet, the answer is that i don't foresee any of them to be effective (enough) - so i have a little time on my hands and I'd like to hear other suggestions or some encouragement .

Thanks in advance ..

 

[StealthFarmer]

Hey Shliite,

Theres a thread in the Growrooom Designs and Equip forum that tells you how to make a DIY Exhaust muffler for around 30 bucks. I haven't tried it yet but it looks like it will do the same thing as those duct mufflers that sell for around eighty bucks at hydro stores.

If you haven't already, I would check that thread out and I would try to make one of those duct mufflers. Its supposed to reduce the whooshing sound made by air rushing out of the ducts.

I have a 6" vortex which was connected to a short piece of duct and it made a pretty loud whooshing noise. I needed to vent my heat out the growroom so I connected a twenty foot piece of regular aluminum ducting to it and it reduced the sound alot.

It probably cuts down on the effectiveness of the fan a little because the air has to travel alot further but my cab is still staying cool and I dont really worry about that wooshing sound no more. Its still there but it cut it down by half or so just by adding a longer piece of ducting to the fan.

If I wasn't so lazy I'd probably make one of those mufflers but I'll save that for another day.... Good luck and let us know how it goes

 

[Budweiser13]

Duct mufflers work check em out........

 

[Rolling_Stoned]

IMHO when silencing a blower, its always a trade off between noise and efficiency.

 

[Nubie Biatch]

Check out the link below. The muffler really helps. I use mine on a 6" vortex. (449CFM)

DIY Fan Muffler

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