Laser-Accurate microphone

[just bob[_2_]]

http://www.engadget.com/2009/09/21/laser-accurate-microphone-proves-once-and-for-all-that-everythin/

I had not been in this group for a while but immediately thought if you all
when I saw this one

[William Sommerwerck]

The idea of a laser microphone has been around almost as long as lasers.
It's interesting that this approach is indirect (rather than "measuring" the
changes in velocity or pressure of the air through which the sound directly
passes).

[Joe Kotroczo]

On 22/09/2009 00:00, in article ,
"William Sommerwerck" > wrote:

> The idea of a laser microphone has been around almost as long as lasers.
> It's interesting that this approach is indirect (rather than "measuring" the
> changes in velocity or pressure of the air through which the sound directly
> passes).

AFAIK Léon Theremin is credited with building the first such device in 1947.
Infrared though, not laser.


--
Joe Kotroczo

[PStamler]

And not the first optical microphone, either. Charles Hoxie of General
Electric patented his "Pallophotophone" optically-sensing microphone/
electrical-recording system in 1921, and Brunswick actually cut
records with it beginning in 1925.

Peace,
Paul

[Scott Dorsey]

PStamler > wrote:
>And not the first optical microphone, either. Charles Hoxie of General
>Electric patented his "Pallophotophone" optically-sensing microphone/
>electrical-recording system in 1921, and Brunswick actually cut
>records with it beginning in 1925.

Bell had a patent on a moving mirror plus selenium cell microphone, didn't
he? Or doesn't that count since it was still mechanical?
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[William Sommerwerck]

>> And not the first optical microphone, either. Charles Hoxie of General
>> Electric patented his "Pallophotophone" optically-sensing microphone/
>> electrical-recording system in 1921, and Brunswick actually cut
>> records with it beginning in 1925.

> Bell had a patent on a moving mirror plus selenium cell microphone,
> didn't he? Or doesn't that count since it was still mechanical?

No, it doesn't count because it was "mechanical". The Pallophotophone
probably was, too. I'd like to see Theremin's design.

The Bell design was later commercialized as the InfraPhone in the early 60s.
There was a "Carl & Jerry" story revolving around it. I had a pair, which I
got for $5 when they were closed out. Wish I still had them.

Any true "optical" microphone has to (I assume) sense very small changes in
the air's refractive index. That was almost certainly impossible with
selenium (or even CdS) cells and noisy tube electronics.

[Don Pearce[_3_]]

On Mon, 21 Sep 2009 23:51:10 -0400, "Soundhaspriority"
> wrote:

>
>"William Sommerwerck" > wrote in message
...
>>>> And not the first optical microphone, either. Charles Hoxie of General
>>>> Electric patented his "Pallophotophone" optically-sensing microphone/
>>>> electrical-recording system in 1921, and Brunswick actually cut
>>>> records with it beginning in 1925.
>>
>>> Bell had a patent on a moving mirror plus selenium cell microphone,
>>> didn't he? Or doesn't that count since it was still mechanical?
>>
>> No, it doesn't count because it was "mechanical". The Pallophotophone
>> probably was, too. I'd like to see Theremin's design.
>>
>> The Bell design was later commercialized as the InfraPhone in the early
>> 60s.
>> There was a "Carl & Jerry" story revolving around it. I had a pair, which
>> I
>> got for $5 when they were closed out. Wish I still had them.
>>
>> Any true "optical" microphone has to (I assume) sense very small changes
>> in
>> the air's refractive index. That was almost certainly impossible with
>> selenium (or even CdS) cells and noisy tube electronics.
>>
>Question intended to provoke thought: Without knowing what this innovation
>sounds like, what is the confidence level that an improvement to microphones
>with practical advantage actually exists?
>
>What would users like to hear that DPA and Schoeps do not already provide?
>
>I can think of one thing, though I don't know how important it is.
>Directional microphones rely on a fictitious estimate of the particle
>velocity created by ducted enclosures. This causes bass response to be
>dependent on distance. A microphone that directly sensed velocity would not
>have this error; frequency response would be independent of distance.
>
>Bob Morein
>(310) 237-6511
>
>

The velocity change is real, not fictitious. I have some calculations
here, the equation is at the end.

http://81.174.169.10/odds/mic

I can see plenty of other potential problems for the mic though,
particularly in linearity which is going to require (if interference
is the operating mechanism) straightening out a sine curve.

d

[Joe Kotroczo]

On 22/09/2009 02:52, in article ,
"William Sommerwerck" > wrote:

>>> And not the first optical microphone, either. Charles Hoxie of General
>>> Electric patented his "Pallophotophone" optically-sensing microphone/
>>> electrical-recording system in 1921, and Brunswick actually cut
>>> records with it beginning in 1925.
>
>> Bell had a patent on a moving mirror plus selenium cell microphone,
>> didn't he? Or doesn't that count since it was still mechanical?
>
> No, it doesn't count because it was "mechanical". The Pallophotophone
> probably was, too. I'd like to see Theremin's design.

Theremins "Buran" is said to have been an infrared beam bounced of the
windows of the American and British embassies in Moscow. Apparently the
usable range was 500m. Also used by Beria to eavesdrop on Stalin.

--
Joe Kotroczo

[Mike Rivers]

William Sommerwerck wrote:

> The Bell design was later commercialized as the InfraPhone in the early 60s.
> There was a "Carl & Jerry" story revolving around it.

Wow! I thought I was the only one around here old enough to know of Carl
& Jerry.
When I was in 7th grade, I met someone in my class who was also
interested in
electronics. He was like Carl and I was like Jerry - both in energy
level and shape.

[Scott Dorsey]

Joe Kotroczo > wrote:
>On 22/09/2009 02:52, in article ,
>"William Sommerwerck" > wrote:
>
>>>> And not the first optical microphone, either. Charles Hoxie of General
>>>> Electric patented his "Pallophotophone" optically-sensing microphone/
>>>> electrical-recording system in 1921, and Brunswick actually cut
>>>> records with it beginning in 1925.
>>
>>> Bell had a patent on a moving mirror plus selenium cell microphone,
>>> didn't he? Or doesn't that count since it was still mechanical?
>>
>> No, it doesn't count because it was "mechanical". The Pallophotophone
>> probably was, too. I'd like to see Theremin's design.
>
>Theremins "Buran" is said to have been an infrared beam bounced of the
>windows of the American and British embassies in Moscow. Apparently the
>usable range was 500m. Also used by Beria to eavesdrop on Stalin.

Again a mechanical system using a moving mirror, like Bell patented many
years earlier. These days I am sure that the trenchcoat guys can get
much longer range with lasers although getting your position absolutely
parallel to the glass becomes that much harder the farther away you are.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Don Pearce[_3_]]

On 22 Sep 2009 07:27:06 -0400, (Scott Dorsey) wrote:

>Joe Kotroczo > wrote:
>>On 22/09/2009 02:52, in article ,
>>"William Sommerwerck" > wrote:
>>
>>>>> And not the first optical microphone, either. Charles Hoxie of General
>>>>> Electric patented his "Pallophotophone" optically-sensing microphone/
>>>>> electrical-recording system in 1921, and Brunswick actually cut
>>>>> records with it beginning in 1925.
>>>
>>>> Bell had a patent on a moving mirror plus selenium cell microphone,
>>>> didn't he? Or doesn't that count since it was still mechanical?
>>>
>>> No, it doesn't count because it was "mechanical". The Pallophotophone
>>> probably was, too. I'd like to see Theremin's design.
>>
>>Theremins "Buran" is said to have been an infrared beam bounced of the
>>windows of the American and British embassies in Moscow. Apparently the
>>usable range was 500m. Also used by Beria to eavesdrop on Stalin.
>
>Again a mechanical system using a moving mirror, like Bell patented many
>years earlier. These days I am sure that the trenchcoat guys can get
>much longer range with lasers although getting your position absolutely
>parallel to the glass becomes that much harder the farther away you are.
>--scott

A laser would be no good for this - the coherence length is far too
great, and all you would receive is a jumble of interference fringes.
Any signal would be utterly buried. The original worked by simple
amplitude modulation by slight alteration of the direction of the beam
under reflection.

In the original you didn't actually need to be perpendicular to the
glass. The light source and receiver didn't need to be in the same
place. As long as you could view a reflection, it worked.

d

[William Sommerwerck]

> Question intended to provoke thought: Without knowing what this
> innovation sounds like, what is the confidence level that an improvement
> to microphones with [a] practical advantage actually exists?
> What would users like to hear that DPA and Schoeps do not already provide?

Genuinely neutral sound.

I'd suggest finding the Stereophile CD that has J Gordon Holt reading one of
his articles using something like 20 different mics -- which all sound
different. I'm intimately familiar with Gordon's voice, but except for the
obviously not-so-good mics, I'd be hard-pressed to say which is most
accurate.

[William Sommerwerck]

>> No, it doesn't count because it was "mechanical". The Pallophotophone
>> probably was, too. I'd like to see Theremin's design.

> Theremin's "Buran" is said to have been an infrared beam bounced of
> the windows of the American and British embassies in Moscow. Apparently
> the usable range was 500m. Also used by Beria to eavesdrop on Stalin.

That's still mechanical (that is, it has a diaphragm).

[Adrian Tuddenham[_2_]]

PStamler > wrote:

> And not the first optical microphone, either. Charles Hoxie of General
> Electric patented his "Pallophotophone" optically-sensing microphone/
> electrical-recording system in 1921, and Brunswick actually cut
> records with it beginning in 1925.

Were records actually made with that microphone, or was it marketing
hype to cover up their unauthorised use of other, more conventional,
patented systems?

The latter has been suggested as a possible explanation because no
Brunswick records of that period have been found on this side of the
pond (UK) which sound like anything other than a moving coil or carbon
granule mic.


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

[Scott Dorsey]

just bob > wrote:
>http://www.engadget.com/2009/09/21/laser-accurate-microphone-proves-once-and-for-all-that-everythin/
>
>I had not been in this group for a while but immediately thought if you all
>when I saw this one

They actually had a mention of the thing in the AES show exhibits description
a couple months ago... it's going to be interesting to see what they actually
bring to the show.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Don Pearce > wrote:
>On 22 Sep 2009 07:27:06 -0400, (Scott Dorsey) wrote:
>>
>>Again a mechanical system using a moving mirror, like Bell patented many
>>years earlier. These days I am sure that the trenchcoat guys can get
>>much longer range with lasers although getting your position absolutely
>>parallel to the glass becomes that much harder the farther away you are.
>
>A laser would be no good for this - the coherence length is far too
>great, and all you would receive is a jumble of interference fringes.
>Any signal would be utterly buried. The original worked by simple
>amplitude modulation by slight alteration of the direction of the beam
>under reflection.

As far as I know, devices today exist to do that also, but they use an IR
laser. Because the laser is very narrow, you can be a great distance
away from the source before there is an issue with spreading. They
still measure the position, not the interference fringes.

>In the original you didn't actually need to be perpendicular to the
>glass. The light source and receiver didn't need to be in the same
>place. As long as you could view a reflection, it worked.

Right, but ultimately you want to have a single device at a single position
rather than two widely separated devices. Less conspicuous.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Don Pearce[_3_]]

On 22 Sep 2009 11:41:58 -0400, (Scott Dorsey) wrote:

>Don Pearce > wrote:
>>On 22 Sep 2009 07:27:06 -0400, (Scott Dorsey) wrote:
>>>
>>>Again a mechanical system using a moving mirror, like Bell patented many
>>>years earlier. These days I am sure that the trenchcoat guys can get
>>>much longer range with lasers although getting your position absolutely
>>>parallel to the glass becomes that much harder the farther away you are.
>>
>>A laser would be no good for this - the coherence length is far too
>>great, and all you would receive is a jumble of interference fringes.
>>Any signal would be utterly buried. The original worked by simple
>>amplitude modulation by slight alteration of the direction of the beam
>>under reflection.
>
>As far as I know, devices today exist to do that also, but they use an IR
>laser. Because the laser is very narrow, you can be a great distance
>away from the source before there is an issue with spreading. They
>still measure the position, not the interference fringes.
>
>>In the original you didn't actually need to be perpendicular to the
>>glass. The light source and receiver didn't need to be in the same
>>place. As long as you could view a reflection, it worked.
>
>Right, but ultimately you want to have a single device at a single position
>rather than two widely separated devices. Less conspicuous.


Well, the light source (even IR) will always be conspicuous, and I
rather like the idea of being nowhere near it while I am listening.

There is an obvious counter of course; something like a mobile phone
vibrator glued to the window would do nicely.

d

[Arny Krueger]

"just bob" > wrote in message

> http://www.engadget.com/2009/09/21/laser-accurate-microphone-proves-once-and-for-all-that-everythin/
>
> I had not been in this group for a while but immediately
> thought if you all when I saw this one

I take it nobody read the press release too closely, or watched any of the
demo videos.

The device is based on a laser sensing the motion due to sound, of the
particles in a column of smoke.

The fox in the chicken coop is the moving column of smoke.

What do you do with a microphone that smokes?

What about turbulence in the moving column of smoke?

How to create am moving column of smoke noiselessly? The demo I saw had a
very audible air pump running in the background.

[PStamler]

On Sep 22, 10:22*am, (Adrian
Tuddenham) wrote:
> PStamler > wrote:
> > And not the first optical microphone, either. Charles Hoxie of General
> > Electric patented his "Pallophotophone" optically-sensing microphone/
> > electrical-recording system in 1921, and Brunswick actually cut
> > records with it beginning in 1925.
>
> Were records actually made with that microphone, or was it marketing
> hype to cover up their unauthorised use of other, more conventional,
> patented systems? *
>
> The latter has been suggested as a possible explanation because no
> Brunswick records of that period have been found on this side of the
> pond (UK) which sound like anything other than a moving coil or carbon
> granule mic.

Good question. My source is Allan Sutton's "Recording the Twenties",
and he provides a good deal of detail about Brunswick's contract with
GE, difficulties in getting good recordings using the system, and
marketing of electrically recorded discs.

I don't know what recordings made with the GE system would have
sounded like; it was a partly-mechanical system, with a small mirror
that moved in response to sound. From Sutton's description, that might
have been a pretty non-linear system.

It's also possible that Brunswick licensed the Pallophotophone system
but only used the electrical cutting head and amplifier, feeding it a
signal from a carbon-granule or condenser mic. That may have happened
with film studios too, when GE spun off the system as "Photophone".

Sutton's book is a good one, but it does contain a few small errors.
This wouldn't be small, though, and he does provide a good deal of
detail about the events surrounding Brunswick's first electrical
recordings.

Peace,
Paul

[Adrian Tuddenham[_2_]]

PStamler > wrote:

> On Sep 22, 10:22*am, (Adrian
> Tuddenham) wrote:
> > PStamler > wrote:
> > > And not the first optical microphone, either. Charles Hoxie of General
> > > Electric patented his "Pallophotophone" optically-sensing microphone/
> > > electrical-recording system in 1921, and Brunswick actually cut
> > > records with it beginning in 1925.
> >
> > Were records actually made with that microphone, or was it marketing
> > hype to cover up their unauthorised use of other, more conventional,
> > patented systems? *
> >
> > The latter has been suggested as a possible explanation because no
> > Brunswick records of that period have been found on this side of the
> > pond (UK) which sound like anything other than a moving coil or carbon
> > granule mic.
>
> Good question. My source is Allan Sutton's "Recording the Twenties",
> and he provides a good deal of detail about Brunswick's contract with
> GE, difficulties in getting good recordings using the system, and
> marketing of electrically recorded discs.
>
> I don't know what recordings made with the GE system would have
> sounded like; it was a partly-mechanical system, with a small mirror
> that moved in response to sound. From Sutton's description, that might
> have been a pretty non-linear system.
>
> It's also possible that Brunswick licensed the Pallophotophone system
> but only used the electrical cutting head and amplifier, feeding it a
> signal from a carbon-granule or condenser mic. That may have happened
> with film studios too, when GE spun off the system as "Photophone".
>
> Sutton's book is a good one, but it does contain a few small errors.
> This wouldn't be small, though, and he does provide a good deal of
> detail about the events surrounding Brunswick's first electrical
> recordings.

I'll see if I can get back to one of my original contacts who raised
that doubt.

In the meantime, if you want a good laugh, look for one of Brunswick's
record sleeves of the period; they show the frequency response going up
to 20 Kc/s. (Presumably they included the record scratch in their
measurements)

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk