if its going to be running in your room as you sleep i strongly suggest you also look beyond the noise from the CPU fan.
of course, an efficient heatsink can use a slow (and thus quiet fan). this can be enhanced by using
A. a large heatsink like the alpha 8045 or the swiftech mcx-462 and a slow fan or
B. using a smaller HS with a 80mm fan and a 60mm to 80mm adaptor.
but thats not all.
i would strongly reccomend you invest in a quality aluminium case, this has a couple of advantages, namely built in quiet casefans and good thermal dissapation, requiring less active cooling all round.
i also suggest a 'whisper' enermax PSU, both for the quality of the PSU and the noise level.
finally look at other things, make sure u have a quiet hard drive, cd rom, and graphics card fan.
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