Adding a rubber strip between the fans and a tight rubber band around them reduces the resonance but they still make quite a lot of noise. These fans are just too loud for this use.
The best result I can report is the following super-simple and effective rubber band mount for the fan:
- I wish I had thought of this earlier.
- rubber-mount.jpg (43.35 KiB) Viewed 17661 times
The band is a slice from a mountain bike tire; quick to make and fit, and very adjustable: sliding the band on the plastic mount points up or down changes the tension on each side of the band, the tighter side pushes the fan in the opposite direction, and you can then adjust the vertical position to the millimeter.
It also holds fans of different thicknesses, so instead of 6mm it could be a more common 10mm or even 15mm. A deeper tunnel makes the fan more efficient and I think you could get the same amount of airflow with a slower-spinning and therefore quieter fan.
You could use a 12V fan at 5V like Dr.BeauWebber did in the thread . For that you need to check the starting voltage of the fan: it varies from model to model, I've seen some with 8, 6, or 4.5V of starting voltage. One that needs more than 5V will not start, or if it is close enough it might spin once you push it but then if it stops for whatever reason it would not start again on its own and your board would fry.
For the Sunon fans, you can find that information in the extended specification PDF from here:
http://www.sunon.com/pro.php?c1=16Select some parameters, for instance size 30x30x10 and voltage 12, then in the result table you have the PDF link at the right side for each model.
Using one fan instead of two the temperature goes up 3 degrees.
In both cases, having the opposite long side of the case in place means around 2 degrees more.
Cheers,
-- Alberto