I got some good help from you guys in this thread, and I'm hoping you can help out again.

This is for the same project: an LED-based torchiere lamp. Cooling for the LED's is to be supplied by an 80mm-square fan, 1" tall. My power supply (discussed at the above link) allows for an adjustable DC supply voltage to the fan, so I can dial the fan RPM down to the lowest (quietest) speed that provides adequate cooling.

Well, I picked this Sunon fan. They brag about their unique bearings and how quiet their fans are, so I decided to try one out. I suppose the bearing itself is quiet, and there's not much wind noise when I slow it down, but the big problem seems to be mechanical vibrations due to the torque pulses caused by the fan's internal ESC switching the current on/off to the motor's poles. Those torque pulses get transmitted to a sheet-metal ductwork assembly that I've built for directing the airflow to the heat sinks, and of course that sheet metal vibrates accordingly. It's unacceptably noisy.

I haven't tried soft-mounting the fan yet; that's something to do this weekend, and will involve securing the fan with soft foam cushions instead of screws. But...if that doesn't work, can anyone recommend an 80mm square fan that really does run quiet? Not just wind noise or bearing noise, but something that mitigates those torque pulses?

 

That fan is not variable its designed for 12v use, you need one like this..
http://www.ebay.com/itm/60mm-25mm-N...CPU-Computer-Ball-Brg-2pin-347a-/180986620372

Failing that why dont you put sound proofing on the ducting like rubber foam pads?
http://www.ebay.co.uk/itm/CAR-VAN-V..._Body_Shop_Supplies_Paint&hash=item336b0cb45f

 

mechanical dampening..

 

That fan is not variable its designed for 12v use, you need one like this..
http://www.ebay.com/itm/60mm-25mm-N...CPU-Computer-Ball-Brg-2pin-347a-/180986620372

It most definitely is variable. If you reduce the supply voltage, the RPM decreases. This is not a matter of conjecture; I've actually done this.

The noise doesn't seem to be related to the supply voltage; if I give it a full 12 volts (per fan spec), the noise is the same quality as it is with lower supply voltages (just proportionately louder).

Failing that why dont you put sound proofing on the ducting like rubber foam pads?

I was hoping to avoid that. The ductwork is extremely complicated: it connects the fan to six different heat sinks arranged in a circle, with the fan in the center exhausting upwards. It was hard enough to make the manifold, covering it with foam would add more complexity. If I can't find another solution, I might have to do this, though...

 

just isolate the fan with rubber washers/gasket or whatever..very common and you are done.