Air duct soundproofing

[Oscar Engber]

I read about using an S-shaped air duct to achieve soundproofing in ventilation in the "soundproofing a garage" article. Do you have (general) specs for constructing such an air duct? I need to keep out noise above approximately 150Hz. If you have any links about constructing a ventilation system that doesn't let sound out I would appreciate it.
/Oscar E

[bjnash]

: I read about using an S-shaped air duct to achieve soundproofing in ventilation in the "soundproofing a garage" article. Do you have (general) specs for constructing such an air duct? I need to keep out noise above approximately 150Hz. If you have any links about constructing a ventilation system that doesn't let sound out I would appreciate it.
: /Oscar E
 Not rocket science!  The duct needs to be at least as big as the air inlet for proper cooling and air transfer.  The length of the center section can be ajusted: the longer it is, the more sound it will have a chance to absorb.     =
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Something like this. Some people have left off the lower angle of the duct, creating an inverted "L" shaped duct with good results.
The key is to line the ducting with sound absorbant mat like our 1/2"  mat.

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