Natural Science Forum / Physics / Acoustics / February 2005

Sorry I don't have any web address, but let's take a look at the noise
generation in the attenuators on a general level. Hope it helps to
understand the problem statement.

It is nore or less common knowledge that, roughly, up to Mach number 0.3
noise generated in ducted systems is dipole-like, meaning that upstream and
downstream levels should be (close to) equal. To my understanding, if the
measured responses vary a lot, this is (mainly) due to different acoustical
characteristics of the upstream and downsteram systems (or some other noise
sources).

The noise generation is roughly descriped (narrow band or broad band) by
appropried Reynolds number. I would expect the upstream noise to be
unmeasurable in case of broadband noise. Narrow band noise response, on the
other hand, is sensitive flow conditions and acoustical systems and their
coupling. There is a lot scientific publications of both types of 'noise
generation', mainly starting from 1960's. These (allways?) consider the
downsteram noise.

ari

Almost all the manufacturers of silencers provide information on the
regenerated or "self noise" of silencers on their data sheets as a function
of velocity or cfm.  This is often done for a specific face area, with an
adjustment table for larger and smaller areas.

Thanks All

Still interested if anyone has more info.

Cheers