The "Deco Box"
By Dave Benz
Posted on December 15, 2004
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PSU Muffler

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Because I wanted the server to be as quiet as possible, I did a lot of research before I designed the case. One popular strategy for silencing a PSU is to hang a "muffler" off the back end of a store-bought case. Another strategy is to build ducts into (or onto) a PC case to help silence it. I decided to build a muffler into the top of the case and then hang the power supply inside the case. I put it in the top to take advantage of convection.

It seems like the point of a car muffler is to maximize air flow while minimizing noise flow. Since these goals match up well with muffling a power supply, I figured it would be a good place to start. Not knowing very much about muffling sound, I chose a generic car muffler design which would be easy to build out of foam.

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I got my crayons out to illustrate the airflow.

Car mufflers use a bunch of different strategies to soften sound, including sound-cancelling echo chambers, sound absorbing materials, band-pass filters, and even little holes drilled into the main exhaust pipe which diffuse the sound. (Click here for a "How Stuff Works" discussion on car mufflers.)

I'm totally out of my depth trying to talk about acoustics and noise dampening, but I figure this design does a couple of things. First off, it doesn't allow sound to exit in a straight line, and forces the sound to travel further to get out. Second, everything is made out of foam, which absorbs the sound as it bounces around. Although I'm not entirely sure, from some things I've read I think this design may also form a band-pass filter of some kind.

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Here's the muffler with the case lid. The foam I used on the lid came from the sleeping bag mat, and as you can see it has something of a egg-crate wave to it, which helps to diffuse the sound. Because of how I hung the power supply inside the case, if I ever needed to replace it, or had some trouble with it, I would need access to the muffler chamber. So I made it in a way that the lid can be taken off. This turned out to be advantagous later.

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Here's a shot of the completed computer with the lid off. You can see how I built an extension cable that goes from the power supply down to the bottom of the case.

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One last shot into the muffler chamber from the back of the case, with the lid on.

As I said before, the Enermax PSU is whisper-quiet already. With the muffler lid off on a normal day in our livingroom, a person can still hear the power supply from about three feet away. Using the muffler, a person has to put their ear to the back of the case to hear anything at all.