Well, turns out that the fans in the Ampro 4000G are powered with 20V. This of course causes the ‘quiet’ vantec fans to run much faster than they would from 12V.
I tried connecting them in serial, effectively giving each fan 10V. They are much quieter, but had a ‘beat’ sound that was sort of annoying. I suspect that this was too low to run them and get them to run smoothly. They may have been causing interference with each other as well.
Having picked up some 47Ohm 1W resistors today, I tried using them to slow the fans down. The down side to this is that I’m creating heat to slow the fans down. Using one 47Ohm resistor cuts the noise quite a bit, but its still too loud for me. I used 2 in series, effectively doubling to 94Ohms. This was quite a bit better, but not ‘silent’. This should have been roughly the equivalent of 14V.
In theory, I need 133Ohm resistor to bring them down to 12V. I’ll have to take another trip to the electronics store.
It seems quite a bit of the noise is due to the mounting of the fans as well. I’ve removed the grills entirely, so there isn’t too much turbulance, but the case seems to vibrate quite a bit from the motion of the fans. I may look into ways to isolate the fans from the case, or dampen the case. Possibly both.
While I was writing this up, I realized that if I used 3x the 47Ohm resistors, I’d be pretty close to 133Ohms. So I ran downstairs to give it a shot. The fan is pretty much silent at this speed. I can’t comment on the ‘beat’ sound since I only have 1 fan running — but interestingly I was attributing a buzz sound to the fan, when it is in fact the long circuit board that runs next to the blue tube. I proved this by running with no fans.
I’m tempted to try using 2 of the 47Ohm resistors in series to slow the fans down to something close to their proper speed, and see how things work out in terms of airflow & cooling.