killswtch.netA geek’s thoughts on various stuff

I received yet more odd looks and comments at work when a few weeks ago I received a delivery of 24 foam tiles. I ordered them from eBay as an experiment in trying to reduce the amount of noise eminating from the rack cabinet. At about £30 it was a bit of a gamble.

The tiles arrived packed in a tower, and were a lot lighter than I expected. I have installed sound absorption material before, inside the HTPC case that used to house boron, but that was specifically designed for noise reduction within computers. This foam was much thinner but had several layers. The bottom layer was very high density and hence quite heavy. The weight is designed to dampen vibration in whatever it’s attached to as well as absorbing sounds. The foam for the cabinet is not layered but it’s much thicker at about 4cm. One of the larger surfaces is flat and the other has an egg-crate relief pattern which apparently prevents the formation of standing waves.

The tiles are normally attached using spray-on adhesive, but to keep costs down I decided to give my glue gun a go. However, since hot-melt glue is obviously a liquid when applying, the foam tended to absorb quite a lot of it rather than presenting it to the side panels to which the foam was being attached. The solution to this was to add more glue and only press very lightly and hold until the glue had cooled. Despite this method, I managed to use up 5 or 6 sticks – my entire supply – doing both sides of the cabinet.

24 tiles turned out to be the exact amount needed. I thought I might only use about 8, but 12 on each side fitted just right. Only 2 offcuts were made as a result of having to account for the 4-way power strip mounted to one of the uprights in the cabinet.

The resulting noise reduction is better than I expected. I can now sleep at night despite the 40mm fans on the two 19″ rackmount switches whirring away. It’s far from totally silent, but the elimination of reflection of the sounds inside the cabinet has greatly reduced the amplitude of the eminating noise, which escapes from the top of the cabinet. I have attempted to add the top to the cabinet which again drastiacally reduced noise, but it caused the temperature inside to rise significantly and I discovered that the top of the cabinet is not square enough to mount the top without modification.