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[TowerTalk] RE: idea(l?) hamshack

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Subject: [TowerTalk] RE: idea(l?) hamshack
From: (Jim Lux)
Date: Mon Jun 2 17:21:30 2003
>Regarding a ceiling fan for ventilation, if I buy a quiet whisper
>bathroom-type ventilation fan do you think I need to worry about EMI from
>the fan?

Those fans are shaded pole, and should have very low noise (other than the 
existing 60 Hz noise you've already got everywhere). Brushed motors are the 
ones that will generate plenty of noise (i.e. vacuum cleaners, blenders, etc.)

>  If so, do you all know of an electrically quieter fan?  Also,
>there was some mention of sound proofing, ideas on where to get this or what
>to use?

Sound proofing is a big topic.. What sounds are you trying to 
suppress?  High, low, internal reflections, etc.

High frequencies are usually reduced by attenuation with multiple 
scattering in stuff like fiberglass or foam.

Low frequencies are attenuated by making them move something lossy and 
massive (lead sheet, sand, etc.)

If all you're looking to do is kill the "liveness" of flat, plain walls, 
then carpet works fairly well at reducing the reverberation time (it 
doesn't attenuate much, but reverberation is a multiple reflection kind of 
thing, so after a few tens of reflections, even a 1 dB loss is a lot)

The real challenge in soundproofing is usually eliminating conduction paths 
(i.e. a standard wall with wood studs is pretty bad... drywall sounding 
board on one side, 4" rigid connection through the stud, then drywall 
sounding board on the other side).. Offset studs (3.5" studs, but wall 
thickness of, say 6", so each side has it's own studs, with the studs 
offset from each other (16" o.c. on each side, but one side is set 8" from 
the other) works fairly well at minimal cost. You could go to 24" o.c. 
studs even.  They make "z-strips" for just this sort of thing. They are 
vibration isolating mounts for the drywall.

Jim, W6RMK 

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