Ask Dan: I want to talk to you about ducts.Date: 23 June 2007 Last modified 03-Dec-2011.
Yes, ducts like this work, though I've got to say $AU22 delivered (Aus PC Market's price - Australian shoppers can click here to order) for a piece of foam-lined plastic is a bit rich for my blood.
Still, it's cheaper than a Lian Li PC-S80, which has a similar duct as standard equipment.
My sound meter wouldn't tell us much, though, because it's impossible to quantify exactly how well one of these things is going to work in a real-world situation. There are too many variables involved.
If you've got an ordinary sort of tower PC with only the power supply as an exhaust fan and maybe one or two fans sucking air in at the front, a large slice of the noise it produces really will be coming out of the PSU grille. That noise shoots straight out of the back of the computer, and then usually encounters a wall and reflects with very little loss out into the room where you can hear it.
A duct that just turns the exhaust air around so it blows down towards the floor will make a significant difference to the noise level if, and only if, the floor is carpeted or similarly softened. If the duct's lined with foam then that'll help a little, but not a huge amount, unless the duct turns another corner or two before it lets the air out.
If you're interested in this idea, then before you spend any money on a commercial product you should try lashing up some hideous arrangement of tape, cardboard and packing foam that does much the same thing. You may well find the jury-rigged version works just fine, especially if it's under your desk where nobody can see it. It may well work better than a pre-built duct, if your computer's got more than one exhaust fan - every noise exit needs to feed into the duct, or it won't achieve a lot.
Other low-dollar passive computer quietening options include:
Softening up hard surfaces around the computer with an old towel or a small rug or something.
Isolating the computer itself from the floor with something a bit squishy (a rubber car floor mat, say) so it transfers less vibration into the floorboards.
Increasing the mass of the computer's side panels so they vibrate less.
I'm not sure what cheap substances would work best for that last job. Clay would be fine for testing purposes; if it worked, you could try screwing a sheet of plywood onto the outside of each side panel. If you've got some old lead-sheet flashing sitting in the shed, you could attach it to the panels with double-sided tape (or a plethora of rare earth magnets, if the case is steel) and get a pleasingly steampunk look.
(A reader's now pointed out that you can get bituminous "asphalt" pads meant for silencing car body panels quite cheaply these days. Check with your local car stereo outfitters. Another reader's pointed out the existence of "barium-loaded vinyl" under various names, which is dense and nonresonant and flexible and not very expensive, if you can find someone who won't try to sell you a box of several 20 foot rolls for $US250.)
Back in the days when dot matrix printers roamed the land (and big offices often had something even louder), you used to be able to buy "printer hutches", which often looked rather like a giant breadbox. Big hinged lid, foam lining, quiet cooling fans.
Compact and portable a printer hutch, or modern recreation of one, is not. But a hutch for a 132-column printer could accommodate a modern mini-tower PC quite comfortably. Or as many as four babies.
Australian shoppers can buy the Silverstone Power Supply Acoustic Cover from Aus PC Market for $AU22
Click here to order!