Unfortunately, all the brands mentioned are flunked in size 60mm with me as too loud or annoying sounds. The Noctua is the first 60s of REALLY is silent.
I bought the fan to 251 finally get my QNAP living room-compatible, because the built-in 70mm fan is very loud (and turns in the lowest level at 900 rpm). Since the holes do not match, I simply plugged the rear through the supplied rubber buffers in the "groove" of the circular fan opening on the unit and connected to the fan. Since the Noctua is rubberized everywhere anyway, he can not give vibrations to the housing of the NAS.
=> It works! The fan keeps bombenfest still and the speed was immediately recognized by the NAS and controlled via PWM fan. Even at high revs (> 900) is directly on the NAS a draft to hear, but no unnecessary noise from the bearings, etc. Thus, in the living room rack completely silent! (Disk accesses one hears of course still).
We flew in, the fan is too low, but do not worry, there's loads of space in the housing of the 251st
At ~ 650 revolutions arise with me following Temps (degrees Celsius):
- CPU 45 degrees
- System 40 degrees
- HDD1 31 degree (WD Red 3TB)
- HDD2 31 degree (WD Red 3TB)
- Fairly high price, but rather once expensive than twice cheap.
- PWM capability (in the 60's I think the only PWM enabled => Top!)
- Great accessories, stop with various cables, vary the speed / at 2000 rpm, the PWM
- Rubber buffer
- Absolute silence, only the draft is at higher speeds from making
If the fan buy definitely again! Those looking for absolute silent fan, is always in good hands with Noctua.