Even if you pay some extra to get low dB fans and set your BIOS to have varying fan speeds it still can be quite far from quiet. 20 dB isn’t that loud, but it’s not silence, and— let us be blunt —adaptive fan speeds seems pretty much to alternate between off and full blast. If your computer is near a wall, the noise reverberates through the room, and the low-frequencies leak in the room on the other side of the wall.
So to muff the sound, I build a “sound shield” made out of custom upholstered panels.
The first thing is to cut the frame. Taking measures isn’t the hard part. To muff my box I needed two panels. One 18″×28″ (w×h) and one 28″×28″ (w×h) to be joined at 90°. I got a few 8’×1½”×¾”, and cut them to 18″, 28″, and 25″ (there are other acceptable cuts to get the desired frame sizes). The next step is to assemble the frames.
The only thing to make sure is that they are absolutely at 90°. You drill holes (just a tiny bit smaller than the screws’ shafts) (glue optional) and you screw them.
When the frames are assembled, they should look like this:
You then pick a rough fabric (which is, I think, more likely to absorb sound) to match your furniture (or scare your co-workers).
You cut the fabric and use a stapler to fasten it to one side of the frame. One or two layer of stuff:
and you’re ready to fasten the other side. I’ve never done this before, and I should advise you to be careful with the staples: make sure they do not poke out on the other side. A finished panel should look like:
(I’ll let you decide whether you think it matches my furniture or scares my coworkers.) The two panels are then assembled at 90° using metal right angles:
Finally, you slide it around the noisy thing: