Re: OT The sound of space?
- From: "William Black" <william.black@xxxxxxxxxxxxx>
- Date: Sun, 2 Sep 2007 22:39:08 +0100
"Michael Bell" <michael@xxxxxxxxxxxxxxxx> wrote in message
news:8d641b1c4f.michaelbell@xxxxxxxxxxxxxxxxxxxxxxxxxxx
I noticed that when I moved my head around the space in front of the
window, the feeling of being in a room with the background hubbub of
voices had vanished, and although I could still hear them (of course,
they were quite close) but the feeling of enclosure had vanished. Why?
Some possible explanations cross the mind :-
There must be two amplifiers, one from inside to outside, and the
other from outside to inside. Is it something to do with the way they
are set up not feedback?
The backside of the windows must be quieter than the public side. Am I
just in the quiet zone created by the outwards amplifier playing the
quiet of the office side? But one sound can't SUBTRACT from another.
Can it?
Yes it can.
Phase differences and 'subtractive mixing' can kill background noise.
A 'noise cancelling microphone' has two microphones.
One at the front and one at the back. The background noise is the same at
both microphones.
If you speak into one end then that microphone has background noise plus
your voice.
Now, electronically subtract the front mic from the back mic and what you
have is the voice minus the background noise.
The electronic subtraction is easy to do.
For a more complicated explanation you'll have to read up on phases in
sound.
--
William Black
I've seen things you people wouldn't believe.
Barbeques on fire by the chalets past the castle headland
I watched the gift shops glitter in the darkness off the Newborough gate
All these moments will be lost in time, like icecream on the beach
Time for tea.
.
- References:
- OT The sound of space?
- From: Michael Bell
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