Timothy Daniels wrote:

"Johannes H Andersen" replied:
Timothy Daniels wrote:

Have you thought about just building a 4-sided plywood box
around it that had cheap carpeting stapled to the inside surfaces?
The box could even have a carpeted floor that didn't extend all
the way to the rear wall so that cables could still drop down
behind the desk. The front and rear walls could be doors that
swung open for access to cables (rear) and to drives (front),
and the front door would be open at the bottom (à la bar room
door) to allow fresh air intake. Essentially, that would be giving
up on quiet fans and relying instead on a sound absorbing partial
cabinet around the case. The reason that companies haven't
offered them is that they are so low tech (and bulky and heavy)
that there would be no profit in them. But that makes them
perfect for the homebuilder.

A problem though with this solution is that it also keep the heat
inside. Sound absorbing material is usually also heat insulating.
Secondly, our sound perception follows a logarithmic scale; a
small audible reduction of 3 dB require a 50% reduction in sound
energy.

Read the description again. There is no top to this cabinet,
and there is free convection in the rear since there is no floor
under the rear cables, and the front door does not go all the way
down to the desk surface. There is no interference with air flow,
and there is no dependence at all on conduction. All this cabinet
does is force most of the sound to bounce at least once off a
carpeted surface. A reduction of more than 50% of sound energy
is easy. I did a crude experiment of just suspending a 2'x3' sheet
of carpet against the wall behind my midi tower, and the reduction
in sound was surprising.

*TimDaniels*

Then you have cut out reflections of noise from the wall. It's OK if
you can remove noise by some simple means. It is unfortunate that the
cabinet sometimes amplifies the noise, I've found that opening the
cabinet on my PC actually reduces the noise, but then it diverts the
airflow which you don't particularly want. Hence there are acoustic
considerations as well. I have tried to shield my PC with a plywood
box, but it gave little result and access was cumbersome if I wanted
to do something. Instead I now have a good CPU heat sink with
temperature control (the CPU fan rarely runs) plus a 50 Ohm 3 Watts
resistor in series with the PSU fan. The PSU fan resistor was
carefully chosen by feeling the temperature of the PSU components.