Audio Cooling – How to Stop Fan Hum

For years I’ve had fans in the back of the audio cabinet to keep my stereo stuff cool. Even modern equipment generates a lot of heat, esp the Receiver or any Amps you have.

When I got this audio cabinet about 8 years ago I put 3 fans in it. I got the best fans that I could find to reduce the hum that fans all make – Vantec Stealth 5″, and a Vantec Stealth 3″ for the center bay. There is a small transformer hooked up to the Aux power of the receiver so that the fans turn on whenever the receiver is on.

Here is what I came up with only now after all these years to quiet the fans:

The original scheme had the fans mounted on a piece of 1/2″ plywood and that is isolated from the very thin cabinet back with 4 screws through grommets. Notice the slot in the plate and cabinet back for cable access. While this doesn’t seal the fan to the cabinet, the cooling does not suffer and cable access is greatly simplified.

See the next photo for the grommets:

The grommets hold the plywood and fan away from the back of the cabinet, but the screw still allows hum to conduct from the fan plate to the cabinet back, which acts like a sound board. The hum was not very annoying, but you could hear it.

In the past the fans were screwed directly to the 1/2″ plywood plate. But the recent idea, which totally deadens the hum, is to isolate the fans from the cabinet back with thin sheets of foam. This is shown in detail in the next photo:

The new scheme adds two thin – door skin 1/8″ plywood – ears to the fan. Then two sheets of open celled foam is glued between these ears and the plywood plate. Using open-cell foam allows the use of wood glue to glue the foam to the wood. Elmer’s or TightBond both work fine. Closed cell foam might work as well if it is rough so the glue can work. Of course you can use contact cement as well to glue the foam. You should pick as swishy a foam as you can find. stiff foam obviously will conduct more vibrations to the cabinet back. Using the foam, there is no solid coupling between the fan and the back of the cabinet. So the sound is completely deadened. It would no longer be necessary to use the grommets at this point. The 1/2″ plywood plate could be attached directly to the cabinet back. If I were doing a new design, I would use thin plywood instead of the 1/2 plywood since the weight of that mounting no longer contributes to the sound isolation.

Finally!! 😀 No fan hum!!

Good luck and I hope this gives you an idea if you have a similar problem,