That is the idea, phase cancellation, but it does have limitations.
About 10 db is all that any of them reduce the ambient noise with the
electronic bit. Plus the ambient noise has to be steady state, like the
roar on an air liner. Other non-steady state noises are not affected as
much. So you hear things like your neighbor's music, the baby crying on
the airplane, and pretty much everything except the white noise which
you don't really notice after a while anyway. One advantage is that you
can carry on a conversation with someone while listening to your music.
In-the-ear phones with good seals can drop the outside sound level
about 30 db. That saves your hearing from the noise and from not having
to turn up the volume to hear the music, but you have to take them off
to carry on a conversation.
Winsor
Long Beach, California, USA
http://homepage.mac.com/wincros/PhotoAlbum3.html
On Apr 12, 2005, at 11:16 PM, Philippe Le Zuikomane wrote:
> Actively cancel out ambient noise while piping the nice musical signal
> into the ear canals. I kinda remember it's something about shifting
> the phase of an identical signal so the resulting soundwaves -
> original noise plus phase-shifted duplicate of it - cancel each other
> out. Scientists on the list please weigh in? - Phil
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