From a review at SPCR:
"To get a PC any closer to silence than the 20-22 dBA/1m noise floor imposed by the quietest desktop hard drives, we have to look at other storage options. With the best low noise fans, it is possible to achieve as much as 20~25 cubic feet per minute at a noise level of <18 dBA/1m. However, the lowest noise achieved by any desktop hard drive has remained unchanged at 20~22 dBA/1m for several years."
One day, when I don't have a server/noise room I can put a hole through the office wall to, I'll build a truely silent case for lots of drives. I've already drawn it up.
It will consist of two long sheets of copper (4-5mm thick) that the drives are stacked closely between. Next bend heaps of 10mm copper tube so it snakes along the outside of the copper sheets, and braze/solder it on for good thermal contact.
Pour a 10cm (4"?) thick walled concrete box to place over the top of the drive array, with two water tubes snaking through to the outside, along with data & power cables. Also set a strong metal bar to act as side handle.
Once set, poured enclosure is placed face down a on sheet of rubber & alum/concrete slab floor/whatever, with h/d's & water pump inside. Full sized copper car/truck radiator
is fixed on top of enclosue for passive cooling & to act as the water res. Dedicated fanless PSU can also sit on top.
Need to swap a drive, flip up enclosure (probably using a car jack!) & remove drive from between copper sheets. Use coloured data cables for easier drive identification. A water flow or temp alarm would be wise in case of pump failure, and a row of LEDs showing drive status would be a nice touch.
Low cost, long lasting, totally silent, fun project to do with kids.
If you don't need true silence (I have a hearing condition that computer noise aggrivates), just use large, low speed fans.
Cheers.