Test Methodology
I use an LW-9266 Fan PQ performance measurement apparatus to evaluate cooling fans. This is a highly sophisticated scientific instrument made in Taiwan by Long Win.
Fan Testing Machine Technical Specifications:
- Manufacturer: Long Win Science & Technology Corporation
- Air Flow Rate: 2.4 – 250 CFM
- Accuracy of Air Flow Rage: <3.5% INFS
- Repeatability error: < 2%
- Static pressure: 0-20mmAq (100mmAq with the high static pressure throttle device)
- Overall Dimensions: 0.7 (W) x 2.2 (L) x 1.6 (H) m
- Power Source: 220VAC, 5A, Single Phase, 50/60Hz
- Based on Standards: ISO 5801-2007, AMCA 210-0, ASHRAE 51-2007, IEC 61591-2005, GB/T 1236-200
Besides the Long Win machine, I also use the following equipment.
Testing Equipment:
- Noise Test Environment: Hemi-Anechoic Chamber with 6 dB(A) noise floor
- Conditions: 25 (+-2) degrees Celsius, 40-50% humidity
- Sound Analyzer: Bruel & Kjaer 2270-S G4
- Microphone: Bruel & Kjaer Type 4955-A
- Mic Calibrator: Bruel & Kjaer Type 4231
- Data Logger: Picoscope TC-08
Pages:
First of all, many thanks Aris!
Well, I was expecting bigger difference at lower RPMs. In the higher I expected very similar results, as it is, because the main source of noise, which covers other sounds, is created by a moving air mass that radiates a sound wave into the environment. And since the geometry of propeller is the same, there should be no major differences.
This 2nd DBB fan is not so disturbing at 10% (although it’s very near) as the 1st DBB (spike at 5 kHz). However, at 25% it is even more annoying than 1st one because of the harmonics/resonance, which starts between 2nd and 3rd second in the recording.
FDB has much nicer sound at 10% and 25% PWM level.
One note: I have one hypothesis as to why the 1st DBB has higher power consumption than the 2nd. The spike at 5 kHz reminds me of grinding/scraping metal on metal. The bearings may not be sufficiently lubricated, or the tolerance of the bearing balls is not tight enough … but its only a guess 😀
for sure there was something wrong with the first sample, since its peak RPM on the longwin were also off.
The double ball bearing model is gone in the US. Arctic decided to change it to FDB.