Run Silent, Go Feep
<p><em>Warning: The following blog entry provides way more than the<br />
recommended daily allowance of geeking. If you don&#8217;t have a serious<br />
propeller-head streak, surf outta here now before it&#8217;s too<br />
late.</em></p>
<p>I&#8217;m mainly a software guy, but occasionally I build PCs for fun.<br />
Design them, rather; the further away I stay from actual hardware the<br />
happier it usually is for everybody.  Last year, I designed an <a href="http://www.catb.org/~esr/writings/ultimate-linux-box">Ultimate<br />
Linux Box</a>; the good folks at <a href="http://www.laclinux.com/">Los Alamos Computers</a> built it and<br />
will cheerfully sell you one.  It was a successful design in most<br />
respects, but unpleasantly noisy.  This year, as we do the 2002<br />
refresh, I&#8217;m going to be working hard at getting the most noise<br />
reduction I can without sacrificing performance.  I&#8217;m experimenting<br />
now with ways and means.</p>
<p>So I spent a couple of hours today disassembling the case of my<br />
wife Cathy&#8217;s machine (minx.thyrsus.com) and lining three sides of it<br />
with <a href="http://www.dynamat.com/">Dynamat</a>, a kind of stick-on<br />
rubber acoustic insulation often used in car-stereo installations.<br />
The malevolent god that normally attends me when I futz with hardware<br />
must have been off tormenting some other hapless ex-mathematician; no<br />
hardware was destroyed, no blood was shed, and I&#8217;m typing this on the<br />
selfsame reassembled machine.</p>
<p>Minx is a pretty generic mid-tower system made with cheap Taiwanese<br />
parts in mid-2002 by my local <a href="http://www.abestpc.com/">hole-in-the-wall computer shop</a>: I<br />
spent only $150 to have it built, recycling a few parts from an only<br />
slightly older machine. It has a 300W power supply, Athlon 950 mobo<br />
with stock CPU cooler fan, one 80mm case fan, 7200RPM ATA drive.  I<br />
succeeded in lining both 14&#8243;-square side panels and the case top; this<br />
used up the 4&#8217;sq piece I bought so efficiently that there was only<br />
about 10&#8243;sq in two small piece left over.  I used those to cover the<br />
only exposed solid section of the back panel.</p>
<p>If you want try this yourself, the tools I found useful were a<br />
utility knife and a metal footrule, the latter useful both for<br />
measuring to fit and as a cutting guide.</p>
<p>I took before and after measurements with the db meter.  dbA scale,<br />
measurements made with the probe one inch above the center-rear edge<br />
of the case.</p>
<table border="1">
<tr>
<td>Machine off:</td>
<td>44dbA</td>
</tr>
<tr>
<td>Machine on, before:</td>
<td>63dbA</td>
</tr>
<tr>
<td>Machine on, after:</td>
<td>61dbA</td>
</tr>
</table>
<p>In other words, only a 2dbA drop &#8212; marginal when you consider<br />
that the meter is only rated 1.5dB accurate! but it&#8217;s worth bearing in<br />
mind that the scale is logarithmic; 2dbA is more than it looks like.</p>
<p>I have studio-engineer ears and sensitive musician fingers.  I took<br />
before-and-after measurements with those, too, listening to the sound<br />
tambre and feeling for case resonance.</p>
<p>My ears tell me that the box is only slightly quieter, but the noise<br />
spectrum has changed.  The proportion of high-frequency noise has<br />
dropped; more of what I&#8217;m hearing is white noise due to turbulant<br />
airflow, less is bearing noise.  This is a good change even if total<br />
emission hasn&#8217;t dropped much.</p>
<p>My fingers tell me that the amount of case resonance has dropped quite<br />
dramatically, especially on the side panels.</p>
<p>Was it worth doing? I am not sure.  There would probably be more<br />
benefit on a system emitting more bearing noise from 10K or 15Krpm<br />
drives.  On this one, I think the power supply is emitting most of<br />
the noise, and acoustic lining can&#8217;t do much against that.</p>
<p>In fact, my clearest take-away from this is that the big gains in<br />
noise reduction on conventional PCs are likely to come from<br />
obsessing about power-supply engineering &#8212; including details like<br />
whether the fan blows through a slotted grille or a cutout with a<br />
wire-basket finger guard (the latter will generate less turbulence<br />
noise).</p>
<p>I&#8217;d like to retrofit minx with a Papst 12dbA muffin fan and see if<br />
that makes a measurable difference.  But the best change would<br />
probably be one of the <a href="http://www.endpcnoise.com/cgi-bin/e/00005.html?id=LhadbVAh">Enhance</a><br />
300W PSUs that are supposed to only emit 26dbA.  I&#8217;ll bet that would<br />
win big.</p>
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