How 12 dBA becomes 25 dBA

[halcyon]

So, you're putting that supa-silent 12 dBA Papst fan into your case and thinking it solves your noise problems.

Think again.

Here's an example how vibration, restriction of airflow and other issues can make even very low dBA rated fans make at least 25 dBA of noise:

http://www.dirkvader.de/page/fan-special.html

I'm sure most of us have already experience this in practise and in effect this is nothing new.

The questions remain, what measure can one take to dampen the noise of a fan once one has already picked the lowest noise fan possible?

Some examples:

- Rubber grommets / attachers instead of screws
www.siliconacoustics.com/fanisolators1.html

- Unrestricted airflow to avoid additional swooshing sounds

- A vibration damper between the fan and the case
www.directron.com/tnpcs90.html

Is there anything else?

Has somebody succesfully modified a good fan to be even more silent after installation?

Of course one can always lower the voltage for less rpm / airflow, but that's not necessarily what I'm after here.

regards,
Halcyon

[jojo4u]

So, you're putting that supa-silent 12 dBA Pabst fan into your case and thinking it solves your noise problems.

These 12dBA are much too low. Only with a very high priced equipment and special rooms you can measure under 20dBA. Look at the reviews here at SPCR....

[dukla2000]

We need to be careful trying to correlate dirkvader's results with published acoustics. Their setup admits to having a hard drive and power supply, the mic is not 1m from the fan and the fans have the AX-7 'obstruction' right in front of their outlet (compared to manufacturers numbers at 1m in free air etc).

The main point they are trying to make is that a Papst 8412NGL is quieter than the others, and an 8412NG about the same as a Panaflo L1A in both noise and cfm (everything at 12V). To me it seems a valid comparison between Papst & Panaflo at 12V.

Has somebody succesfully modified a good fan to be even more silent after installation?

I have started 'lapping' my fans with about 400grit paper around the blade edges. Very gently, just to remove any imperfections. Not sure that they are more silent (get me that extreme sound lab cause I am talking about a Papst 8412NGL at 12V and an NMB 4710NL-04W-B10-P00 at 7V) but at least I feel better!!

[ez2remember]

Firstly the 12dBA is over exagerated, no way is it 12dBA!

A fan mounted inside a PSU will cause a lot of noise even if you cut out all the fan grills. The fan is too close to the internal components of the PSU such as the heatsink, wires, capacitors etc. I have a decoupled Panaflo 80mm L1A@7v mounted outside of my PSU and it made a huge difference in noise compared to it being on the inside, which caused a lot of air turbulance from the inlet side.

The farther the fan is away from anything from it's path the less noise it will cause, although maybe undectectable to the human ear as long as there is atleast a small gap. So free air is quieter, nothing to block it's path from the inlet or exhaust side, which causes air turbulance.