Here are 4ea brand-new, yet unpackaged fans for testing, and the tool needed to open the Enermax Cluster package:
The fans are the A-C PWM 1500RPM, the Scythe PWM 1200RPM, the Enermax Cluster PWM fan at 1200RPM, and the 1200RPM Slipstream 3-pin fan to provide a reference for the PWM fans. A white spot was added to the plain black hubs so a stroboscope could be used to measure RPM:
First, I tested the four fans to see which pushed the least air at 100% (or 12.00V for the Slipstream). The Scythe PWM proved the weakest by a small margin, with 611sensorRPM at 100%. The Cluster was almost identical, while the A-C needed to be turned down to 82% (as you would expect from a higher RPM part). The Slipstream pushed even more air that the A-C, with a sensorRPM of 848 at 12.00V.
Kama PWM 100% 48.0dBA .5" 611sensor 1292fanRPM (39.0dBA @5")
50% 38.4dBA .5" 332sensor 759fanRPM
Clus PWM 100% 48.2dBA .5" 611sensor 1275fanRPM
50% 35.9dBA .5" 361sensor 794fanRPM
A-C PWM 82% 48.4dBA .5" (note 1) 1198fanRPM
42% 33.2dBA .5" (note 2) 556fanRPM
Slipstr 6.84V 40.6dBA .5" 611sensor 932fanRPM
A cautionary note: the A-C PWM was the last fan tested. I was getting anomolous sensor RPMs, a small anomoly at first (note 1) and a whopper at the last (note 2), where I measured 474RPM that should have been in the mid-to-upper 300s. I repeated that test 4 times and got 474sensor 4 times. If the fan was really
pushing that much air, the fan RPM and the noise level should have been higher... but they weren't.
This 120mm fixture was the first I constructed. The sensor prop shaft was originally taped to the pylon, and since the pylon was not put on completely straight, I just bent the prop shaft. This fixture, and its plastic sensor prop, have seen a great deal of use. I repeat, the problem showed up on the last fan and was much worse on the second of two measurements.
You should know this, and decide for yourself how much trust to put in the above figures. I didn't measure the Slipstream at half-RPM because the noise reading would have been near the ambient (27.9dBA, as usual). And, I measured the Slipstream before I measured the A-C.
My other fixtures - 92, 80, and 60mm - incorporated things learned on the 120mm fixture, esp. re the sensor prop assembly. No bent shafts! I've started building a new 120mm fixture with the same improvements.
Now, pretending that nothing is amiss, note that all the PWM fans had the same noise levels near 100%, but there are definite differences lower down (the A-C is quietest there). All the PWM fans are 7.4 to 7.8dBA noisier than the Slipstream when near 100%. This is something to think about when deciding on 3-pin or PWM fans.
I didn't use a 5" distance for the noise measurements - except one - because the reading is 9dBA lower and would have placed some of the other readings below the ambient noise. Similarly, I couldn't measure the noise levels at 30% PWM.
edit: changed "at" to "with" and "constant" to "equal" in the title.