On Saturday, 23 June 2018 10:47:50 UTC+1, Chris J Dixon wrote:
tabbypurr wrote:

If you can feel it as vibration it's definitely low frequency. Get yourself the relevant equipment & try it.

I once spent some time on a project in a simple form of anechoic
chamber, and it was indeed quite strange.

As I was doing tests near the hearing threshold, I set up my kit
with a sound level meter, which happened to have a scope output.
Out of curiosity, I had a look at things with a flat response
selected (instead if the usual "A" weighting), and was surprised
how much low frequency stuff there was about.

it's an unavoidable problem with microphones. Normal movements cause very large amplitude infrasonics, ever accompanied by harmonics.

One odd aspect was that, although external airborne noise was
well suppressed, they hadn't managed fully to isolate the chamber
from the basement floor it stood on. There was a railway line
about 1/4 mile away, and although I never ever heard a passing
train outside the chamber, inside they were clearly audible.

Chris

it's hard to achieve complete isolation. Electronic suspension technology can do it, but afaik it's impractical passively. One way or another the weight has to be carried, and that means a connection with some stiffness & thus coupling.


NT