small audible reduction of 3 dB require a 50% reduction in sound
energy.

o The letter after dB is the Weighting applied
---- (A) is used for humans - poor at 25dB(A) since it is an approximation
-------- qualitative nature of the noise becomes important
-------- for fans bearing choice, vibration, resonance, blade-to-housing gap
---- (A) is really aimed at industrial noise
-------- hence there is a new ISO standard aimed at super-silent noise
levels

o A reduction of 10dB(A) is a 50% reduction in sound energy
---- 3dB(A) is the margin most people can detect
---- however this too depends on the noise level re 20s or 70s

o Each 180-degree turn you make sound go thro reduces it 6dB(A)

o The most cost effective sound dampening is treating the Cause
---- then treat the Effect - which is much more difficult re sound-proofing
-------- you have lots of holes in a PC
-------- you have case-fans outside the soundproofing inside the case
-------- CPU-fan / drives / soundproofing / case-fan / ear :-)

QuietPC 3-pk soundproofing is very good re price - good peelable stick,
since it's very heavy & ok closed-cell foam. Of course the foam is a bit
lame as it's just ~5mm thick (limited by PC space in present designs).

You need mass for low frequency, and closed-cell foam for high frequency.
Most PC sound emitters are few milli-watt, so it's a foam issue vs just
mass.
Resonance is an issue re fan & other motorised object mounting & vibration.

Treat cause, treating effect is more difficult.

The new BTX form-factor will initially solve a lot of problems:
o Blow thro heatsink, blow thro PC design -- like the G5
---- that will allow sub 30dB(A) PCs
o However CPU & Graphics & HD power output are rising fast
---- 125W CPUs are the first, and frankly dual-CPU machines will hit 400W
---- IDE HDs are moving from 7200rpm to 10,000rpm & SCSI beyond 15300rpm

So the silence may be short-lived - but at least better than the ATX
alternative.

Have fun :-)
--
Dorothy Bradbury, backup email:
www.stores.ebay.co.uk/panaflofan (Ebay)
http://homepage.ntlworld.com/dorothy...ry/panaflo.htm (Free 1st-Class
Shipping)