View Single Post
  #9   Report Post  
Posted to rec.audio.pro
Frank Stearns
 
Posts: n/a
Default Reducing ventelation noise

Jay Kadis writes:

In article .com,
"Matrixmusic" wrote:


I have 6 inch ventelation going into my studio and it's causing noise.
Any suggestions on how to reduce the noise floor through muffling the
noise
kevin


Is the noise from the air handlers or from turbulence in the ducts?


There are duct lining products that can reduce noise, but low-noise A/C systems
for studios employ oversized ducts with very low air flows rates to avoid
turbulence and that won't be attainable with 6" ducts.


That's always true, but sometimes you also have to punt.

Our mobile rig has 6" flexi ducting to an external AC unit. Fan noise was
griping me. Investigated duct silencers, but they cost Big Bucks and were
bulky.

Found a cut-away picture of one such animal. Stupidly simple concept.

At both ends of each duct, I cobbled together duct slats the duct diameter
(plus a bit to make for a snug fit) and about 10" in length, made from 1"
703, "v"d at the wind edge of the slat to avoid (as much) turbulance, and
wrapped with cloth so that fiberglass dust wouldn't spew into the space.

Shoved two such slats down the flexiduct, one after the other, but turned
90 degrees to each. Same on both ends; same for both the plenum and
return. (Total of eight of these slats.)

Dead, I mean DEAD quiet. The only way you could tell it was running was to
feel the cool air moving. I'm guessing some 30-40 dB noise reduction (and
for about $10 in 703 and cloth vs. $500 minimum for a commercial unit.

You will lose some duct capacity, but fiddle with the cross-area numbers
of the duct and what's taken by the edge-on of the slats. 10-15% loss
isn't too bad, and it works really well, at least for us.

Hope the helps,

Frank Stearns
Mobile Audio
--