On Tue, 29 Jul 2014 13:47:00 -0700 (PDT), whit3rd
wrote:

On Tuesday, July 29, 2014 10:55:47 AM UTC-7, wrote:
I'm building a box to hold a small compress[or].
Can anybody recommend a filter or filter material that reduces noise
transmission but still allows air to pass through it?

Anything that has different sound propogation than air will work.
I'd be tempted to start with coarse steel wool contained by screen
wire. Alas, low frequency noise will require some thickness of
filter to get any attenuation.

For best performance, use distance: put the compressor on the
roof, and run extra plumbing and wire length.

The garage works well. I'd do something like that for dust, too,
except that it moves too much air (kinda the idea).