Turn Your House Into Noise Cancellation Headphones

glen herrmannsfeldt wrote:
In comp.dsp CWatters <colin.watters_at_noturnersoakspam.plus.com> wrote:
On 15/09/2011 16:45, Bret Cahill wrote:

The system could monitor the location of the head of each person in
the room.

That's not the main problem.

The difficulty is getting the antinoise signal to the persons head
without it being audible at another persons head.

If you get the noise low at the walls, it should (on average) stay
low throughout the room. That can take a lot of microphones and
speakers, as the frequency increases.

In fact it's worse than that. Even when there is only one person, the
anti noise needed to suppress noise in one ear is a source of noise that
has to be suppressed in the other ear.

At some point, it is an N variables and N unknowns problem.
For N people in 3D, you have 3N variables, so you need at least 3N
speakers to select the phase for. (Well, maybe one less.) More
will get you larger, depending on wavelength, regions around the head.

Unless you figure out how to make sound waves incredibly directional
(for all frequencies) I can't see how it can be done.

If you have a whole wall of microphones outside, and speakers inside,
each adjusted with the appropriate delay (though the wall) and
amplitude (how much leaks through the wall that needs cancelling)
then, for wavelengths somewhat longer than the speaker spacing it
should pretty much cancel throughout the room.

But the other speaking person is part of that noise. If the OP
is a guy, can't he just use his selective hearing software? )))

On Saturday, September 17, 2011 12:01:15 PM UTC-7, John Larkin wrote:
On Sat, 17 Sep 2011 11:38:07 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:

On Friday, September 16, 2011 3:16:54 PM UTC-7, John Larkin wrote:
On Fri, 16 Sep 2011 13:37:49 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:

For more on this subject, refer to Arthur Clarke's _Tales from the White Hart_,

Is that the story where the noise canceler exploded?

But consider: the power output of the device has to cancel sound,
thus reducing the energy in the room.

COE is part of the problem. If a transducer were somehow intelligent
enough to cancel the sound pressure at some usefully distant volume in
a room (unlikely, but take it as a hypothetical) it will be net
outputting sound.

No, not at all. One might cancel the fluctuations at a point by output of energy
but that merely creates a NODE of the soundwaves. If you cancel the sound
fluctuations in a room-sized or house-sized volume, that's equivalent
to salting the region with completely efficient energy-harvesters.

There is some otherwise nice real estate at the end of Navy runways,
neighborhoods in San Diego and Virginia Beach where pilots practice
taking off an aircraft carrier with after burners wide open.

A lot of residents would be willing to pay $5,000 or more to be able
to talk to other people in a room at the flip of a switch. If it
draws a lot of power or when there is little outdoor noise it might be
desirable to turn it off or have it automatically turn off after 5
minutes and then back on as soon as the noise exceeds a threshold.

Noise cancellation should be cheaper than redoing the walls and in
some ways it might be an easier problem than headphones where the
distances involved are only a cm.

A few noisy zones might be tolerable as long as the locations of quiet
zones in a room could be moved and adjusted.

Maybe I missed it, but in all the proposals that have been
bandied about here, nobody seems to have suggested "simple"
servo systems:

Dealing for the moment only with noise that
gets into the house via transmission through the walls, we
can envision walls covered with active panels. Each uses a
servo system to hold a stationary position. If the interior
of the wall doesn't move, then no sound passes through it.

Of course, to handle high frequencies would require a *lot*
of small servo panels.

OK, I didn't say it would be *easy*. But maybe easier than
dealing with microphone arrays, speaker arrays, head
tracking, phase cancellation, etc, etc, etc.

Once we've dealt with wall transmission, we can deal with
windows. Suppose the window glass is gripped at the edges
(out of sight) by drivers that can apply bending forces.
They could also sense bending to derive the feedback signal,
but we'd probably need to supplement that with something
like an IR reflection scheme to pick up more central
motions.

Lastly, sound entry via ductwork is probably the easiest to
deal with. (As I recall, ducts were the first things to
have ANC applied successfully, decades before headphones.)

Of course, to power all these servos will require your own
electrical generation plant... noisy, but now we know how to
deal with that!

Best regards,

Bob Masta

DAQARTA v6.02
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
Science with your sound card!- Hide quoted text -

- Show quoted text -

BTW, what's the hold up on clear conductors and magnets with a low
index of refraction? If you don't have some Law of Nature that states
transparent is impossible you have exactly thirty (30) days to
producing clear conductors and magnets.

On Sat, 17 Sep 2011 15:37:24 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:

... If you cancel the sound
fluctuations in a room-sized or house-sized volume, that's equivalent
to salting the region with completely efficient energy-harvesters.

That's not what people usually think of as noise canceling. I think.

So you could make the outer wall of a house out of thousands of tiny
speakers...
Concrete-filled cinder blocks might work, too.

BTW, what's the hold up on clear conductors and magnets with a low
index of refraction? If you don't have some Law of Nature that states
transparent is impossible you have exactly thirty (30) days to
producing clear conductors and magnets.

...  If you cancel the sound
fluctuations in a room-sized or house-sized volume, that's equivalent
to salting the region with completely efficient energy-harvesters.

That's not what people usually think of as noise canceling. I think.

So you could make the outer wall of a house out of thousands of tiny
speakers...
Concrete-filled cinder blocks might work, too.

Air velocity in a sound wave becomes zero at the surface of a concrete block
but again, that's only in ONE dimension, normal to the block's surface; the
block surface is an enforced node of one of the three velocity components
of the soundwave.   Similarly, 'speaker' transducers can only cancel one of
the three components of impinging waves.  So, neither approach will
replicate the idealized sci-fi gadget.   Fog, though (because there's an
asymmetry in overpressure-condensation and underpressure-evaporation
on the water droplets) has possibilities.