81 lines
4.7 KiB
Plaintext
81 lines
4.7 KiB
Plaintext
Run Silent, Go Feep
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<p><em>Warning: The following blog entry provides way more than the<br />
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recommended daily allowance of geeking. If you don’t have a serious<br />
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propeller-head streak, surf outta here now before it’s too<br />
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late.</em></p>
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<p>I’m mainly a software guy, but occasionally I build PCs for fun.<br />
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Design them, rather; the further away I stay from actual hardware the<br />
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happier it usually is for everybody. Last year, I designed an <a href="http://www.catb.org/~esr/writings/ultimate-linux-box">Ultimate<br />
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Linux Box</a>; the good folks at <a href="http://www.laclinux.com/">Los Alamos Computers</a> built it and<br />
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will cheerfully sell you one. It was a successful design in most<br />
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respects, but unpleasantly noisy. This year, as we do the 2002<br />
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refresh, I’m going to be working hard at getting the most noise<br />
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reduction I can without sacrificing performance. I’m experimenting<br />
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now with ways and means.</p>
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<p>So I spent a couple of hours today disassembling the case of my<br />
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wife Cathy’s machine (minx.thyrsus.com) and lining three sides of it<br />
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with <a href="http://www.dynamat.com/">Dynamat</a>, a kind of stick-on<br />
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rubber acoustic insulation often used in car-stereo installations.<br />
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The malevolent god that normally attends me when I futz with hardware<br />
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must have been off tormenting some other hapless ex-mathematician; no<br />
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hardware was destroyed, no blood was shed, and I’m typing this on the<br />
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selfsame reassembled machine.</p>
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<p>Minx is a pretty generic mid-tower system made with cheap Taiwanese<br />
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parts in mid-2002 by my local <a href="http://www.abestpc.com/">hole-in-the-wall computer shop</a>: I<br />
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spent only $150 to have it built, recycling a few parts from an only<br />
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slightly older machine. It has a 300W power supply, Athlon 950 mobo<br />
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with stock CPU cooler fan, one 80mm case fan, 7200RPM ATA drive. I<br />
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succeeded in lining both 14″-square side panels and the case top; this<br />
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used up the 4’sq piece I bought so efficiently that there was only<br />
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about 10″sq in two small piece left over. I used those to cover the<br />
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only exposed solid section of the back panel.</p>
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<p>If you want try this yourself, the tools I found useful were a<br />
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utility knife and a metal footrule, the latter useful both for<br />
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measuring to fit and as a cutting guide.</p>
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<p>I took before and after measurements with the db meter. dbA scale,<br />
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measurements made with the probe one inch above the center-rear edge<br />
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of the case.</p>
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<table border="1">
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<tr>
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<td>Machine off:</td>
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<td>44dbA</td>
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</tr>
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<tr>
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<td>Machine on, before:</td>
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<td>63dbA</td>
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</tr>
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<tr>
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<td>Machine on, after:</td>
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<td>61dbA</td>
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</tr>
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</table>
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<p>In other words, only a 2dbA drop — marginal when you consider<br />
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that the meter is only rated 1.5dB accurate! but it’s worth bearing in<br />
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mind that the scale is logarithmic; 2dbA is more than it looks like.</p>
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<p>I have studio-engineer ears and sensitive musician fingers. I took<br />
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before-and-after measurements with those, too, listening to the sound<br />
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tambre and feeling for case resonance.</p>
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<p>My ears tell me that the box is only slightly quieter, but the noise<br />
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spectrum has changed. The proportion of high-frequency noise has<br />
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dropped; more of what I’m hearing is white noise due to turbulant<br />
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airflow, less is bearing noise. This is a good change even if total<br />
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emission hasn’t dropped much.</p>
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<p>My fingers tell me that the amount of case resonance has dropped quite<br />
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dramatically, especially on the side panels.</p>
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<p>Was it worth doing? I am not sure. There would probably be more<br />
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benefit on a system emitting more bearing noise from 10K or 15Krpm<br />
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drives. On this one, I think the power supply is emitting most of<br />
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the noise, and acoustic lining can’t do much against that.</p>
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<p>In fact, my clearest take-away from this is that the big gains in<br />
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noise reduction on conventional PCs are likely to come from<br />
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obsessing about power-supply engineering — including details like<br />
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whether the fan blows through a slotted grille or a cutout with a<br />
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wire-basket finger guard (the latter will generate less turbulence<br />
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noise).</p>
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<p>I’d like to retrofit minx with a Papst 12dbA muffin fan and see if<br />
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that makes a measurable difference. But the best change would<br />
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probably be one of the <a href="http://www.endpcnoise.com/cgi-bin/e/00005.html?id=LhadbVAh">Enhance</a><br />
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300W PSUs that are supposed to only emit 26dbA. I’ll bet that would<br />
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win big.</p>
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<p><a href="http://enetation.co.uk/comments.php?user=esr&commentid=79200649">Blogspot comments</a></p>
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