Noise Blocking Servo Headphones & Servo Mics

[Bret Cahill]

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:

This is actually fundamentally different than the speaker microphone
solution. Servos are about keeping something still. Speakers and
microphones are about movement.

The current could be measured for a "servo mic."

A servo system, of course, requires something stationary. This could
easily be done with small panels that are perpendicular to the noise
blocking panel. Only the component of sound that is perpendicular to
the panel needs to be blocked and that won't appear much in the
perpendicular panels.

Except maybe for the cost -- and it's not even clear why servo systems
are so expensive anyway -- it's interesting why this isn't done with
[noise blocking] headphones.

Does anyone know of any cheap servo systems? Bose sells noise
cancellation headphones for less than $200. Force balance
accelerometers like those on missile guidance systems cost over
$1,000.

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.

The real problem is the high dynamic response of hearing. A 90%
reduction in the noise "power" seems like a 10% reduction in noise so
a small space between adjacent panels or the door and jam might be way
too much for a satisfactory reduction in noise.

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

High frequencies can be damped by conventional passive materials,
foams etc.


Bret Cahill

 

[Chiron613]

On Tue, 20 Sep 2011 10:18:22 -0700, Bret Cahill wrote:

<snip>

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

This is actually fundamentally different than the speaker microphone
solution. Servos are about keeping something still. Speakers and
microphones are about movement.

The current could be measured for a "servo mic."

A servo system, of course, requires something stationary. This could
easily be done with small panels that are perpendicular to the noise
blocking panel. Only the component of sound that is perpendicular to
the panel needs to be blocked and that won't appear much in the
perpendicular panels.

Except maybe for the cost -- and it's not even clear why servo systems
are so expensive anyway -- it's interesting why this isn't done with
[noise blocking] headphones.

Does anyone know of any cheap servo systems? Bose sells noise
cancellation headphones for less than $200. Force balance
accelerometers like those on missile guidance systems cost over $1,000.

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.

The real problem is the high dynamic response of hearing. A 90%
reduction in the noise "power" seems like a 10% reduction in noise so a
small space between adjacent panels or the door and jam might be way too
much for a satisfactory reduction in noise.

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

High frequencies can be damped by conventional passive materials, foams
etc.


Bret Cahill

I'm thinking it might be feasible using a negative feedback arrangement
with panels perhaps driven capacitively. I seem to recall seeing a
circuit that worked something like that - though I don't know whether it
was for a headphone or a larger space. I don't know how practical it
would be to have entire walls that functioned as speakers - and I doubt
it would be a big hit with people who care about decorating... but the
idea is intriguing.




--
I can't understand it. I can't even understand the people who can
understand it.
-- Queen Juliana of the Netherlands.

 

[Bret Cahill]

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

This is actually fundamentally different than the speaker microphone
solution.  Servos are about keeping something still.  Speakers and
microphones are about movement.

The current could be measured for a "servo mic."

A servo system, of course, requires something stationary.  This could
easily be done with small panels that are perpendicular to the noise
blocking panel.  Only the component of sound that is perpendicular to
the panel needs to be blocked and that won't appear much in the
perpendicular panels.

Except maybe for the cost -- and it's not even clear why servo systems
are so expensive anyway -- it's interesting why this isn't done with
[noise blocking] headphones.

Does anyone know of any cheap servo systems?  Bose sells noise
cancellation headphones for less than $200.  Force balance
accelerometers like those on missile guidance systems cost over $1,000.

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.

The real problem is the high dynamic response of hearing.  A 90%
reduction in the noise "power" seems like a 10% reduction in noise so a
small space between adjacent panels or the door and jam might be way too
much for a satisfactory reduction in noise.

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

High frequencies can be damped by conventional passive materials, foams
etc.

Bret Cahill

I'm thinking it might be feasible using a negative feedback arrangement
with panels perhaps driven capacitively.  

At first glance it seems like that would much simpler, infinitely more
uniform, much cheaper and more energy efficient than lots of coils and
magnets.

A "capacitor panel" would need to be able to be charged / discharged
in less than a millisecond and to balance the acoustical "pressure"
the electrostatic "pressure" may have to be large.

Anyone have any ball park numbers for caps that would summarily rule
this out? How many microns can a cap squeeze inward? If it requires
92 kV maybe it's not ready for Home Depot.

With 3 layers the panel facing outside would accelerate to and from
the middle panel squeezing and expanding the dielectric material.
That voltage could then be used to squeeze or expand the dielectric
between the panel facing inside and the middle panel.

A plus pressure causes the overall panel to get thinner and a "minus"
pressure thicker so that the inside panel never moves.

It would be interesting to see if it was possible to get something to
work with the "servo" inherent in the design, i.e., with nothing more
complicated than one or 2 DC voltage sources.

I seem to recall seeing a
circuit that worked something like that - though I don't know whether it
was for a headphone or a larger space.  I don't know how practical it
would be to have entire walls that functioned as speakers - and I doubt
it would be a big hit with people who care about decorating... but the
idea is intriguing.

If it was easy to roll up like wall paper. Someone mentioned a clear
conductor so windows could be made to work as well.

Building codes now require builders use [passive] sound proofing
materials. The problem with this is you can't hear what's outside
when the jets are gone.

Silence should be possible with the flip of a switch.


Bret Cahill

 

[Bob Masta]

On Wed, 21 Sep 2011 08:21:34 -0700 (PDT), Bret Cahill
<Bret_E_Cahill@yahoo.com> wrote:

Maybe I missed it, but in all the proposals that have been bandied
about here, nobody seems to have suggested =A0"simple" servo systems:

This is actually fundamentally different than the speaker microphone
solution. =A0Servos are about keeping something still. =A0Speakers and
microphones are about movement.

The current could be measured for a "servo mic."

A servo system, of course, requires something stationary. =A0This could
easily be done with small panels that are perpendicular to the noise
blocking panel. =A0Only the component of sound that is perpendicular to
the panel needs to be blocked and that won't appear much in the
perpendicular panels.

Except maybe for the cost -- and it's not even clear why servo systems
are so expensive anyway -- it's interesting why this isn't done with
[noise blocking] headphones.

Does anyone know of any cheap servo systems? =A0Bose sells noise
cancellation headphones for less than $200. =A0Force balance
accelerometers like those on missile guidance systems cost over $1,000.

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. =A0Each uses a servo system to hold a stationary positi=
on.
=A0If the interior of the wall doesn't move, then no sound passes thro=
ugh
it.

The real problem is the high dynamic response of hearing. =A0A 90%
reduction in the noise "power" seems like a 10% reduction in noise so a
small space between adjacent panels or the door and jam might be way to=
o
much for a satisfactory reduction in noise.

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

High frequencies can be damped by conventional passive materials, foams
etc.

Bret Cahill

I'm thinking it might be feasible using a negative feedback arrangement
with panels perhaps driven capacitively. =A0

At first glance it seems like that would much simpler, infinitely more
uniform, much cheaper and more energy efficient than lots of coils and
magnets.

A "capacitor panel" would need to be able to be charged / discharged
in less than a millisecond and to balance the acoustical "pressure"
the electrostatic "pressure" may have to be large.

Anyone have any ball park numbers for caps that would summarily rule
this out? How many microns can a cap squeeze inward? If it requires
92 kV maybe it's not ready for Home Depot.

With 3 layers the panel facing outside would accelerate to and from
the middle panel squeezing and expanding the dielectric material.
That voltage could then be used to squeeze or expand the dielectric
between the panel facing inside and the middle panel.

A plus pressure causes the overall panel to get thinner and a "minus"
pressure thicker so that the inside panel never moves.

It would be interesting to see if it was possible to get something to
work with the "servo" inherent in the design, i.e., with nothing more
complicated than one or 2 DC voltage sources.

Look into "electrostatic speaker drivers". They are fairly
simple arrays that you can build yourself. They typically
have a thin aluminized mylar film suspended between metal
grids. You apply a high bias voltage (5000 V or so)
between the metal grids, and you run the output of your
stereo through a big step-up transformer.

They have the best high frequency response of any speaker
type, very smooth and extended. They are not very sensitive
unless the panels are large. The problem is that the high
frequencies are coming from a large flat panel, so they
"beam" straight out... the opposite of the ideal point
source that radiates equally in all directions. So you have
to align them to point at your favorite listening chair.

Obviously, that would be no good for noise cancellation. As
noted previously, the drivers need to be small to cancel
high frequencies. But then I think you would run into
problems because with less suspended area, the edge
stiffness of the suspension (where the film is clamped)
would dominate and the sensitivity would drop even further
than the simple reduction in area would imply. But you
can't raise the grid or driving voltage too high, or you get
arcing.

In short, bad idea... and that doesn't even consider the
issues with using them as sensors.

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!

 

[Bret Cahill]

Maybe I missed it, but in all the proposals that have been bandied
about here, nobody seems to have suggested =A0"simple" servo systems:

This is actually fundamentally different than the speaker microphone
solution. =A0Servos are about keeping something still. =A0Speakers and
microphones are about movement.

The current could be measured for a "servo mic."

A servo system, of course, requires something stationary. =A0This could
easily be done with small panels that are perpendicular to the noise
blocking panel. =A0Only the component of sound that is perpendicular to
the panel needs to be blocked and that won't appear much in the
perpendicular panels.

Except maybe for the cost -- and it's not even clear why servo systems
are so expensive anyway -- it's interesting why this isn't done with
[noise blocking] headphones.

Does anyone know of any cheap servo systems? =A0Bose sells noise
cancellation headphones for less than $200. =A0Force balance
accelerometers like those on missile guidance systems cost over $1,000.

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. =A0Each uses a servo system to hold a stationary positi> >on.
=A0If the interior of the wall doesn't move, then no sound passes thro> >ugh
it.

The real problem is the high dynamic response of hearing. =A0A 90%
reduction in the noise "power" seems like a 10% reduction in noise so a
small space between adjacent panels or the door and jam might be way to> >o
much for a satisfactory reduction in noise.

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

High frequencies can be damped by conventional passive materials, foams
etc.

Bret Cahill

I'm thinking it might be feasible using a negative feedback arrangement
with panels perhaps driven capacitively. =A0

At first glance it seems like that would much simpler, infinitely more
uniform, much cheaper and more energy efficient than lots of coils and
magnets.

A "capacitor panel" would need to be able to be charged / discharged
in less than a millisecond and to balance the acoustical "pressure"
the electrostatic "pressure" may have to be large.

Anyone have any ball park numbers for caps that would summarily rule
this out?  How many microns can a cap squeeze inward?  If it requires
92 kV maybe it's not ready for Home Depot.

With 3 layers the panel facing outside would accelerate to and from
the middle panel squeezing and expanding the dielectric material.
That voltage could then be used to squeeze or expand the dielectric
between the panel facing inside and the middle panel.

A plus pressure causes the overall panel to get thinner and a "minus"
pressure thicker so that the inside panel never moves.

It would be interesting to see if it was possible to get something to
work with the "servo" inherent in the design, i.e., with nothing more
complicated than one or 2 DC voltage sources.

Look into "electrostatic speaker drivers".  They are fairly
simple arrays that you can build yourself.  They typically
have a thin aluminized mylar film suspended between metal
grids.  You apply a high bias voltage (5000 V or so)
between the metal grids, and you run the output of your
stereo through a big step-up transformer.  

They have the best high frequency response of any speaker
type, very smooth and extended.  They are not very sensitive
unless the panels are large. The problem is that the high
frequencies are coming from a large flat panel, so they
"beam" straight out... the opposite of the ideal point
source that radiates equally in all directions.  So you have
to align them to point at your favorite listening chair.

Obviously, that would be no good for noise cancellation.  As
noted previously, the drivers need to be small to cancel
high frequencies.  

If "high frequency" means anything over 2 kHz then maybe that can best
be done with conventional / passive materials.

But then I think you would run into
problems because with less suspended area, the edge
stiffness of the suspension (where the film is clamped)
would dominate and the sensitivity would drop even further
than the simple reduction in area would imply.  But you
can't raise the grid or driving voltage too high, or you get
arcing.

Large displacement caused by the sound => high voltage voltage in
caps.

In short, bad idea... and that doesn't even consider the
issues with using them as sensors.

Using the panel as a sensor might not be all that much of an
advantage.

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 -

 

[Chiron613]

On Wed, 21 Sep 2011 08:21:34 -0700, Bret Cahill wrote:

<snip>

I'm thinking it might be feasible using a negative feedback arrangement
with panels perhaps driven capacitively.

At first glance it seems like that would much simpler, infinitely more
uniform, much cheaper and more energy efficient than lots of coils and
magnets.

A "capacitor panel" would need to be able to be charged / discharged in
less than a millisecond and to balance the acoustical "pressure" the
electrostatic "pressure" may have to be large.

Anyone have any ball park numbers for caps that would summarily rule
this out? How many microns can a cap squeeze inward? If it requires 92
kV maybe it's not ready for Home Depot.

snip

OK, maybe I am using the wrong term here. I wasn't suggesting to use
capacitors to drive the panel; but that the whole panel itself could act
as a large capacitor with one of the plates free to move.

The free-moving "plate" (probably a thin plastic film with a metallic
conductive surface) would be driven by a voltage in response to the noise
(but of opposite sign, so as to cancel it). The other "plate" of the
capacitor could be wire mesh, the holes allowing air to move quickly so
as to permit adequate motion of the film.

The reason I suggest this arrangement is that it seems it would require
far less energy to operate, than trying to use speakers driven by
inductors.

I actually made a "speaker" as I described, just as a sort of proof of
concept thing. It worked, after a fashion (note that I wasn't trying for
noise cancellation, just to see whether capacitive speakers were even
possible).

I just Googled "capacitive speakers," and found that they're definitely
possible and being sold.

So the main question is whether they'd be any good for canceling noise.
I suppose they'd require a large range of motion and quick response
time. I don't know whether that would be practical. But someone might
want to give it a shot...

Silence should be possible with the flip of a switch.

Agreed.

--
<miguel> any new sendmail hole I have to fix before going on vacations?
-- Seen on #Linux

 

[Bob Masta]

On Sat, 24 Sep 2011 07:10:35 GMT, Chiron613
<chiron613@gmail.com> wrote:

On Wed, 21 Sep 2011 08:21:34 -0700, Bret Cahill wrote:

snip

I'm thinking it might be feasible using a negative feedback arrangement
with panels perhaps driven capacitively.

At first glance it seems like that would much simpler, infinitely more
uniform, much cheaper and more energy efficient than lots of coils and
magnets.

A "capacitor panel" would need to be able to be charged / discharged in
less than a millisecond and to balance the acoustical "pressure" the
electrostatic "pressure" may have to be large.

Anyone have any ball park numbers for caps that would summarily rule
this out? How many microns can a cap squeeze inward? If it requires 92
kV maybe it's not ready for Home Depot.

snip

OK, maybe I am using the wrong term here. I wasn't suggesting to use
capacitors to drive the panel; but that the whole panel itself could act
as a large capacitor with one of the plates free to move.

The free-moving "plate" (probably a thin plastic film with a metallic
conductive surface) would be driven by a voltage in response to the noise
(but of opposite sign, so as to cancel it). The other "plate" of the
capacitor could be wire mesh, the holes allowing air to move quickly so
as to permit adequate motion of the film.

The reason I suggest this arrangement is that it seems it would require
far less energy to operate, than trying to use speakers driven by
inductors.

I actually made a "speaker" as I described, just as a sort of proof of
concept thing. It worked, after a fashion (note that I wasn't trying for
noise cancellation, just to see whether capacitive speakers were even
possible).

I just Googled "capacitive speakers," and found that they're definitely
possible and being sold.

So the main question is whether they'd be any good for canceling noise.
I suppose they'd require a large range of motion and quick response
time. I don't know whether that would be practical. But someone might
want to give it a shot...

See my previous response about electrostatic speakers. I
have no information on whether they are more or less
efficient (in terms of energy use) than conventional voice
coil speakers, especially after you take into account the
high voltages needed. But they definitely have problems
with large signals on the one hand and sensitivity on the
other (without arcing).

Note that there is another problem with the simple 2-plate
(membrane and grid) capacitor scheme you mention: The
response is *way* less linear, actually a square law. This
is not a deal-breaker for a servo system that is only trying
to maintain a stationary position, but it's bad news for
sound reproduction.

I used to work in a university lab where we did basic
research on hearing mechanisms of the inner ear. We used
guinea pigs, mostly. We needed to provide loud
high-frequency sound (in the 20 kHz range) in order to
stimulate the part of the inner ear that we were studying.
(The high frequency sensory "hair cells" are the first ones
the incoming sound encounters, with progressively lower
frequencies handled by cells farther along.)

We needed to deliver the sound directly into the ear canal
to avoid problems with head orientation and such. We used a
1/2 inch "condenser" (capacitor) microphone driven in
reverse, driving a short ear tube. The mic is a thin metal
membrane held very close to (but insulated from) a metal
backing plate. The rated voltage was just over 300V before
arcing. The attraction or repulsion forces acting on the
membrane are proportional to the square of the applied
voltage, such that the force is the same regardless of which
plate is positive or negative.

The "standard" approach was to just apply 200V bias to the
membrane, and apply the desired signal on top of that, up to
+/-100V. It wasn't perfect, since this was still a
square-law system, but the resultant 2nd harmonic distortion
was low enough to not cause a problem, usually.

I did build a special square root circuit to reduce the
distortion, but it was more trouble than it was worth, as I
recall.

For pure tones, which is what we mostly used, we could
actually omit the bias and apply +/-300V directly at *half*
the frequency, since the square of a sine is another sine at
2x the frequency. The problem was that when the tone
started (ramped up carefully to control the spectral
splatter) the membrane had to move from a resting position
to a new average value, which caused a "thump" on top of the
tone if we brought it up too fast. So, we used that only
for long ongoing stimuli, not transient bursts.

Ahh, the good old days... <g>

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!

 

[Bret Cahill]

I'm thinking it might be feasible using a negative feedback arrangement
with panels perhaps driven capacitively.

At first glance it seems like that would much simpler, infinitely more
uniform, much cheaper and more energy efficient than lots of coils and
magnets.

A "capacitor panel" would need to be able to be charged / discharged in
less than a millisecond and to balance the acoustical "pressure" the
electrostatic "pressure" may have to be large.

Anyone have any ball park numbers for caps that would summarily rule
this out?  How many microns can a cap squeeze inward?  If it requires 92
kV maybe it's not ready for Home Depot.

snip

OK, maybe I am using the wrong term here.  I wasn't suggesting to use
capacitors to drive the panel; but that the whole panel itself could act
as a large capacitor with one of the plates free to move.

It was originally understood as a single large area, i.e., 8' by 15',
flate cap.

On the other hand, if a lot of "speakers" or non moving panels are
required, it is probably cheap and easy to divide and wire the mylar
into sections.

The free-moving "plate" (probably a thin plastic film with a metallic
conductive surface) would be driven by a voltage in response to the noise
(but of opposite sign, so as to cancel it).  The other "plate" of the
capacitor could be wire mesh, the holes allowing air to move quickly so
as to permit adequate motion of the film.

The reason I suggest this arrangement is that it seems it would require
far less energy to operate, than trying to use speakers driven by
inductors.

I actually made a "speaker" as I described, just as a sort of proof of
concept thing.  It worked, after a fashion (note that I wasn't trying for
noise cancellation, just to see whether capacitive speakers were even
possible).

I just Googled "capacitive speakers," and found that they're definitely
possible and being sold.

So the main question is whether they'd be any good for canceling noise.  
I suppose they'd require a large range of motion and quick response
time.  I don't know whether that would be practical.  But someone might
want to give it a shot...

Preferably it should come rolled up like wall paper.

Silence should be possible with the flip of a switch.

Agreed.

Or some automatic noise threshold switch.


Bret Cahill