As with my previous review the first thing to consider is that the db rating doesn't tell the whole story. Tone, resonance and other factors can be more important than pure sound levels.
Motor wine and rhythmic speed related clicking may not show up on the sound meter but when present I can confirm that they are very apparent and can be annoyingly intrusive. On the flip side you could have a fan that made no discernable whining or clicking but was 'showing' as rating high on decibels!
Alpenföhn Föhn 140.
The Föhn 140 is certainly the big brother to the 120. A great quiet performance in terms of the dB rating but once again I noticed an inherent clicking. As I've mentioned before it could well be down to the PWM motor on board pulsing at the lower voltages.
Indeed, running at 12v there is no discernable 'clicking' noise only the whooshing of the fan blades - drop the voltage to 7 or even 5 and the clicking rears its ugly head.
Besides the clicking there is no motor whine, no resonances and no chuffing. At 12v back pressure is excellent but is somewhat at the expense of noise. A couple of these in a PC case will certainly be noticeable. It's very quiet at 7v however and still maintains a good pressure - at 5v it's virtually silent but back pressure does suffer.
I'd also like to point out that although tested at 5v the fan was unable to spin up at this ultra low voltage. That being said, I do find this unsurprising as Alpenföhn only state that the Föhn 140's operating voltage ranges from 7v to 13.2v. If you did want to run this fan at 5v it will happily do it you'd just have to start it up at 7v+ and then reduce voltage.
Lastly the Föhn 140's rubber frame and mounts certainly help aid quiet operation and the inclusion of both the 120mm and 140mm mount holes are certainly a thoughtful design addition too.
