from an earlier posting, repeated as reference:
YL SM 1041RPM 560prop 48.2dBA
GW NCB 970RPM 560prop 44.9dBA (NCB sample #2)
SC PWM 910RPM 560prop 48.6dBA Kama PWM 100%
AC PWM 902RPM 560prop 46.1dBA Arctic Cooling PWM 100%
UC12EB 880RPM 560prop 41.2dBA (a sweet-sounding fan)
SilenX 866RPM 560prop 45.4dBA "11dBA" version
SFlexE 852RPM 560prop 42.3dBA (quieter than NCB!)
9blade 686RPM 560prop 39.6dBA Scythe SlipStream
The above measurements were made under zero backpressure conditions: free air! All
of the fan measurements us SPCR folks encounter are made under zero backpressure, whether by the staff of SPCR or in anechoic chambers by big business. Since we commonly use fans exhaust hot air from cases or to cool HSFs, both of which involve backpressure, these measurements aren't very helpful. But they're the best data we've had available.
Here's how that can be fixed: Use a single HS such as the Thermalright U120E (TRUE). Use a single airflow sensor propeller to measure the airflow provided by various fans (when mounted on the TRUE) and adjust the fan voltages so all the airflows are the same (equal airflow); see above for the free-air example. Measure the fan noise under equal airflow conditions through the HSF fins
(again, see above example). The lowest noise level wins.
Two possible configurations, upstream (air source) to downstream (air destination):
1) Sensor prop, fan under test mounted on the TRUE, TRUE with sensor prop as close as possible to the fan.
2) Fan under test mounted on the TRUE with the sensor as close as possible to the backside of TRUE.
This test should NOT be performed in a PC case or on a mobo. The TRUE has no reason to be mounted on a CPU socket; all we're measuring is the effect of the HSF fins on airflow. My present equal airflow fixtures (for 120, 92, 80, 60mm fans) are standalone devices and need no PC.
PC systems with HSFs like the TRUE always have exhaust fans to overcome the resistances associated with the case.
The above is an exceedingly simple (and obvious) extension of my existing equal-airflow test jigs (which work fine).