The U.L.N.A is very simple to install, (it’s simply a 3 pin extension with a resistor) and lowers the actual RPM of the fan, reducing the noise even further.

E-tailing for around about £14.99 GBP (~$29.00 USD), a bit more expensive than your average quiet fan but really good value for money. 

I took the two thermal probes I have in my rig, and installed one on the inside compartment where the fan draws most of the air out, and one at the rear in the fan's exhaust. This would measure the temperature of the area which is being cooled, and also of the air being extracted from the case.

I ran the test under idle and load for 10 minutes each with both fans, and then the NF-S12 with the U.L.N.A installed. (The load test I used was 3D Mark 2003 running a full benchmark)

The Aspire fan;

The NF-S12;