Damping rear fan noise with a foam-lined pvc pipe

Yomat · Post by **Yomat** » Tue Jun 17, 2003 8:50 pm

Noone doubts that its possible.

Keep us updated on progress/degress.

cuban8 · Post by **cuban8** » Sat Jun 21, 2003 1:02 pm

edlight,

Do you know the science behind this or did you just stumble across it?

The reason I ask is because I had an idea and am looking for someone who understands the science behind noise cancellation.

jafb2000 · Post by **jafb2000** » Sat Jun 21, 2003 4:17 pm

Noise absorption is bad enough, cancellation very difficult.

Using directional change is cancellation but not by "magic",
ie, there is a cost to it as will become clear (albeit small here).

o Everytime you turn sound thro 180-degrees
o You reduce the noise level by 6dB(A)
---- thro superposition of out-of-phase waves.
o You also reduce the cfm slightly
---- however in this case it is very small re 90-degree turn

In this application you are stopping a clear line of sight for
the noise out of the PC case from the hard surfaces in front
of the fan (and the fan) against the wall and at your ears.

If you line the labyrinth you also use a trick in soundproofing:
o Soundproofing parallel to the front of a speaker
---- your soundproofing is just 6mm thick
o Soundproofing sheets perpendicular to the front of a speaker
---- your soundproofing is as thick as the sheets are long

Soundproofing works best by:
o Force sound waves along it, multiple reflections & absorptions
o Reflecting sound waves front it, preventing "line of sight" exit
---- so increasing the /effective distance/ of the sound absorber

Obviously PC cases have "line of sight" exits thro fan holes and
acoustically transparent materials, plus many holes & gaps in PCs!

Breaking the line of sight & multiple holes is difficult.
However, realise how much noise can come thro a tiny hole.