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Mix Magazine

This installment of The Bitstream column appeared in the January 2004 issue of Mix Magazine.

The Bitstream

This column discusses acoustical and electrical noise reduction techniques for computers…

The Sound of Silence

Wellie, wellie, well, it’s 2004 already. Where’s my flying car? But seriously, it’s a new year and I sincerely hope this is the one during which our economy miraculously wakes up from its long slumber…Thanks so much, George and friends.

Heads up, all you underpaid musicians and engineers…It’s fairly easy to find an older computer for FREE, or less than $50 at least, that someone has in their closet gathering dust. The price is right but, you’d probably not want it sitting next to you when your working, since the noise it makes will ruin your day. Last month I was discussing an open source DAW, so this month, let’s take a look at some hardware aspects of that DIY DAW by taking what is close to a FREE COMPUTER (that always gets your attention, doesn’t it?) or nearly so and shutting up everything that creates so darn much acoustical noise. In a word or three: a silent PC.

There are actually two considerations in this whole effort to quiet down a garden variety PC, one being electrical and the other acoustical. Let’s start with electrical or RFI noise within the box making its way into your sound card. Suffice it to say that you want both directions of analog conversion outside the case, otherwise you’re asking for a less than ideal noise floor in your signal paths. Granted, with careful grounding and shielding, it’s possible to convince an analog converter to make nice in such a hostile environment but, why fight it? Better to simply take an electrical digital audio signal, either AES/EBU Type I or Type II unbalanced, MADI, USB or Firewire, out of the computer and convert it externally. Notice I didn’t say optical since POF (Plastic Optical Fiber) is high loss and thus jitter-prone so, unless cable lengths are kept short, it’s crap. Once the data’s outside the case, convert it to analog using the best that your budget can afford and, boom, you’re there…wherever “there” is for you.

As to RFI/EMI escaping the box, one has to assume that the entire case is conductive, grounded and all air gaps in the case are conductively gasketed. Though I can’t imagine not having one already included inside your PeeCee, an inline filter on the incoming AC goes a long way at keeping the power cord, all 3 prongs intact please, from becoming a noise–radiating antenna.

OK, so we’ve got the radio spectrum noise dealt with, now let’s take a look at the acoustical issues. Motors, turbulence–induced noise and mechanical resonances: the three strepitant horsemen of the acoustical apocalypse. The number one problem is motors: they cause the other two problems so, if we could eliminate them entirely, we’d be way ahead of the game. This is possible to do as long as the high current drawing parts, like the CPU, are cooled in some unconventional manner.

Cooling a CPU the old school way entails increasing the surface area of a passive heat sink, which is great if you’re not using a modern, hot running Intel part. Another approach is water cooling, quite common in over–clocking circles (see Pedants below…), while a third method of waste heat removal is heat pipes, either of which requires coupling to oversized heat sinks, a viable if not visually pleasing and space saving choice. Heat pipes (see Pedants below…) distribute the unwanted heat to the farthest reaches of the heat sink and, from there, convection transfers the heat to the surrounding air. A fourth option, which seems to have fallen somewhat out of favor due to efficiency and design limitations, not to mention reliability issues, is to use yet more electrical current to run a Peltier device (see Pedants below…), usually in conjunction with water cooling or heat pipes. Despite the drawbacks of earlier designs, modern Peltier coolers lend themselves nicely to a silent PC outcome. By the way, the water cooling thing is basically an active alternative to passive heat pipes that uses forced cool water instead of a volatile working fluid.

Right then, let’s assume we’ve cooled down the CPU, graphic card, disk drive and any other toasty thing in the case. How about reducing the waste heat itself rather than simply (re)moving it? Power factor correction in the power supply is one answer. Without getting into the gory details of power factor correction and having everyone’s eye balls roll back in your head from dweeb overload, suffice it to say that better quality power supplies incorporate additional electronics that greatly improve the efficiency of the unit. This means less waste heat to remove from the case, so look out for that feature if your budget permits.

On to turbulence…If you must incorporate a fan, run it as slowly as possible to reduce chaotic air flow. Smoothly flowing air makes little or no noise as long as the velocity isn’t too high. Most fans make a racket because they create turbulent flow on their blades or through the surrounding housing. Thermostatically–controlled fans reduce the blade speed unless more cooling is needed and sophisticated blade and venturi housing designs smooth the air flow, reducing a fan’s operating noise. As an example, Apple Computer chose an inexpensive, proven forced air cooling design for their new G5 Tower, but also chose to employ nine independent, thermostatically–controlled fans in four separate chambers with perforated metal front and rear fascia to keep everything cool and quiet. Each fan runs at optimal speed and the large, 35% perforated surface area ensures low turbulence while preventing RFI leakage.

We’re closing in on our ephemeral goal but, wait, I haven’t talked about resonances. Whether it’s cheap, sheet metal cases or thin metal grills, “ya gets whats ya pay for…” and what you get is buzz and rattle. There are many materials that damp vibration and they all work by adding mass to the offending part. Whether it’s strategically placed lumps of Mortite or carefully applied sheets of Dynamat, you can bet that adding a pound of prevention is worth far more than an ounce of cure.

Humm, we’ve gotten rid of every source of noise that we can but, somehow it’s still not quiet enough. Once you’ve exhausted all other options, your only choices are to fall back onto the old tried and true: stick the whole ’puter in an enclosure or remote it with a KVM. Recent innovations in enclosure design from AcoustiLock include those self same heat pipes to transport heat from the noisy and hot interior to the quiet and cool exterior. Other than that, a basic acoustic labyrinth concept, either actively cooled or passive, remains the most effective and inexpensive choice. It was June of 2000 when I last visited the subject of KVMs, devices that remotely provide keyboard, monitor and mouse functions to one or more computers. These days, the latest thang is an embedded web server with IP connectivity, which replaces the old, hardwired style with an Ethernet connection and any web browser — simple and cost effective if you already have a run of UTP or unshielded twisted pair.

That’s about all for this month’s Bitstream. I hope you found this little survey useful and also that this new year brings renewed health, happiness and prosperity to you all. See you next month!


Between a bevy of phone consults and a bout of GPS madness, OMas took time to soak in the unalloyed mayhem of Sergio Leone’s The Good, The Bad, And The Ugly and the bright, sophisticated bop of McCoy Tyner’s The Real McCoy.

Pedant In A Box

This month’s timely technobabble includes…


To over–clock is to modify a computer’s clock circuitry, Millennium Falcon style, in an attempt to improve performance. A higher clock speed means more operations per second which in turn means more useful work done per unit time. Unfortunately, it also means drawing more current in what is usually an already heat–stressed part, not good for reliability. [back]

Heat Pipe

A heat pipe is simply a sealed tube that contains a wick and a liquid that vaporizes at a relatively low temperature. If you heat up one end of the pipe, the liquid at that end vaporizes, which dries out the wick. Cool liquid moves, wicks actually, into the hot end of the tube while the newly created vapor condenses back into liquid at the cold end, replenishing the supply of liquid for the wick to suck up…and the whole process goes ’round and ’round. The result is that heat is drawn away from the hot end, raising the temperature of the cold end, all without any external power requirements save the heat source itself.

Peltier Device

Named after Monsieur Jean Charles Athanase Peltier, who demonstrated the thermoelectric effect that bears his name way back in 1834. Peltier devices are solid state, thermoelectric heat pumps that, in response to an applied electrical current, move heat from one physical side of the device, the “cold” side, to the other, “hot” side in direct proportion to the current applied. If the polarity is reversed, the “pumping” changes direction.

Modern Peltier coolers use such exotic semiconductors as bismuth telluride doped with selenium and antimony. The Sharper Image, that bastion of questionable exotica, sells a “trim, discreet,” personal “climate–control system” utilizing a Peltier device. Now, that’s dope!