Why not closed loop speaker amplification?

[Chris Carlen]

Greetings:

My recent experiences with motion control, coupled with an interest in
audio, have led me to the following question:

Why aren't speakers driven closed loop? Ie, have a position sensor on
the speaker diaphragm, and drive the speaker in a servo loop?

I realize this would be challenging particularly for tweaters (which
also don't necessarily exhibit "stiff" diaphragm movement), but the
concept is more of what I am interested in.

Has this been done? It would seem to be the "holy grail" to have the
speaker cones move in lockstep with the signal waveform.


Just pondering.


Good day!



--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

 

[Kalman Rubinson]

On 7 Jun 2005 09:45:24 -0700, bill.sloman@ieee.org wrote:

It has been done - some years ago Philips used to sell loudspeakers
that worked on this principle. They weren't all that good, probably
because the position of the diaphragm is measured at one point, and the
diaphragm, not being infinitely rigid, distorts under load.

IIRR Philips used an accelerometer mounted on the drive coil as their
"position" sensor.

And it is currently being done on many 'servo' subwoofers.

Kal

 

[Mike Monett]

bill.sloman@ieee.org wrote:

[...]

It has been done - some years ago Philips used to sell loudspeakers
that worked on this principle. They weren't all that good, probably
because the position of the diaphragm is measured at one point, and the
diaphragm, not being infinitely rigid, distorts under load.

IIRR Philips used an accelerometer mounted on the drive coil as their
"position" sensor.

Bill Sloman, Nijmegen

Bill,

You triggered an old memory of a feedback winding adjacent to the main
coil. While looking for it, I came across the following:

----------------------------------------------------------------------
Voigt, Not Black

Editor:

I was surprised to find Martin Colloms---and John Atkinson in his
footnote---perpetuating the notion that Harold Black "invented" feedback
(January '98, p.87). As I recently pointed out elsewhere (Hi-Fi World,
April 1997), that honor belongs to the British engineer Paul Voigt, a
pioneer of high fidelity, who had incorporated it in his Motional
Feedback Patent 231,972, dated January 29, 1924. Over 70 years later,
motional feedback as applied to loudspeakers has made little further
progress, and Voigt's use therein of selective negative feedback, which
he regarded as obvious and not worthy of special attention, is the first
reliably documented use of which I am aware---many years before the Black
disclosure. I enclose a copy of Voigt's circuit in the patent, and a
description of its operation in his own words that shows that he fully
understood its application. The latter is taken from papers in my
possession, typed and annotated by him in August 1970, and reads as
follows:

(read the rest at http://stereophile.com/reference/70/index7.html)

So it appears negative feedback occurred earlier than textbooks state,
and involved our favorite topic - hifi. This should have generated some
choice phrases for John's collection.

Mike Monett

 

[Mark]

On Tue, 07 Jun 2005 13:10:47 -0400, Mike Monett <no@spam.com> wrote:

bill.sloman@ieee.org wrote:

[...]

It has been done - some years ago Philips used to sell loudspeakers
that worked on this principle. They weren't all that good, probably
because the position of the diaphragm is measured at one point, and the
diaphragm, not being infinitely rigid, distorts under load.

IIRR Philips used an accelerometer mounted on the drive coil as their
"position" sensor.

Bill Sloman, Nijmegen

Bill,

You triggered an old memory of a feedback winding adjacent to the main
coil. While looking for it, I came across the following:

----------------------------------------------------------------------
Voigt, Not Black

Editor:

I was surprised to find Martin Colloms---and John Atkinson in his
footnote---perpetuating the notion that Harold Black "invented" feedback
(January '98, p.87). As I recently pointed out elsewhere (Hi-Fi World,
April 1997), that honor belongs to the British engineer Paul Voigt, a
pioneer of high fidelity, who had incorporated it in his Motional
Feedback Patent 231,972, dated January 29, 1924. Over 70 years later,
motional feedback as applied to loudspeakers has made little further
progress, and Voigt's use therein of selective negative feedback, which
he regarded as obvious and not worthy of special attention, is the first
reliably documented use of which I am aware---many years before the Black
disclosure. I enclose a copy of Voigt's circuit in the patent, and a
description of its operation in his own words that shows that he fully
understood its application. The latter is taken from papers in my
possession, typed and annotated by him in August 1970, and reads as
follows:

(read the rest at http://stereophile.com/reference/70/index7.html)

So it appears negative feedback occurred earlier than textbooks state,
and involved our favorite topic - hifi. This should have generated some
choice phrases for John's collection.

Mike Monett

I am sure there was an Elektor Circuit many many years ago that used a
negative feedback system.

 

[R.Lewis]

"Kalman Rubinson" <kr4@nyu.edu> wrote in message
news:6hkba1ht2pvoj0uabmsnf92elru4nrsm62@4ax.com...

On 7 Jun 2005 09:45:24 -0700, bill.sloman@ieee.org wrote:

It has been done - some years ago Philips used to sell loudspeakers
that worked on this principle. They weren't all that good, probably
because the position of the diaphragm is measured at one point, and the
diaphragm, not being infinitely rigid, distorts under load.

IIRR Philips used an accelerometer mounted on the drive coil as their
"position" sensor.

And it is currently being done on many 'servo' subwoofers.

Kal

generally referred to as 'motional feedback'.

 

[Jim Thompson]

On Tue, 7 Jun 2005 19:24:04 +0100, "R.Lewis" <h.lewis@connect-2.co.uk>
wrote:

"Kalman Rubinson" <kr4@nyu.edu> wrote in message
news:6hkba1ht2pvoj0uabmsnf92elru4nrsm62@4ax.com...
On 7 Jun 2005 09:45:24 -0700, bill.sloman@ieee.org wrote:

It has been done - some years ago Philips used to sell loudspeakers
that worked on this principle. They weren't all that good, probably
because the position of the diaphragm is measured at one point, and the
diaphragm, not being infinitely rigid, distorts under load.

IIRR Philips used an accelerometer mounted on the drive coil as their
"position" sensor.

And it is currently being done on many 'servo' subwoofers.

Kal

generally referred to as 'motional feedback'.

Or 'emotional feedback' ;-)

What low frequency corner can be achieved this way?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Kevin Aylward]

Mike Monett wrote:

bill.sloman@ieee.org wrote:

[...]

It has been done - some years ago Philips used to sell loudspeakers
that worked on this principle. They weren't all that good, probably
because the position of the diaphragm is measured at one point, and
the diaphragm, not being infinitely rigid, distorts under load.

IIRR Philips used an accelerometer mounted on the drive coil as their
"position" sensor.

Bill Sloman, Nijmegen

Bill,

You triggered an old memory of a feedback winding adjacent to the main
coil. While looking for it, I came across the following:

----------------------------------------------------------------------
Voigt, Not Black

Editor:

I was surprised to find Martin Colloms---and John Atkinson in his
footnote---perpetuating the notion that Harold Black "invented"
feedback (January '98, p.87). As I recently pointed out elsewhere
(Hi-Fi World, April 1997), that honor belongs to the British engineer
Paul Voigt, a pioneer of high fidelity, who had incorporated it in
his Motional Feedback Patent 231,972, dated January 29, 1924. Over 70
years later, motional feedback as applied to loudspeakers has made
little further progress, and Voigt's use therein of selective
negative feedback, which he regarded as obvious and not worthy of
special attention, is the first reliably documented use of which I am
aware---many years before the Black disclosure. I enclose a copy of
Voigt's circuit in the patent, and a description of its operation in
his own words that shows that he fully understood its application.
The latter is taken from papers in my possession, typed and annotated
by him in August 1970, and reads as follows:

(read the rest at http://stereophile.com/reference/70/index7.html)

So it appears negative feedback occurred earlier than textbooks state,
and involved our favorite topic - hifi. This should have generated
some choice phrases for John's collection.

It occurred way before then. To wit, steam engines had a governor to
regulate speed.


Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[mike]

Chris Carlen wrote:

Greetings:

My recent experiences with motion control, coupled with an interest in
audio, have led me to the following question:

Why aren't speakers driven closed loop? Ie, have a position sensor on
the speaker diaphragm, and drive the speaker in a servo loop?

I realize this would be challenging particularly for tweaters (which
also don't necessarily exhibit "stiff" diaphragm movement), but the
concept is more of what I am interested in.

Has this been done? It would seem to be the "holy grail" to have the
speaker cones move in lockstep with the signal waveform.


Just pondering.


Good day!

I did a bunch of experiments back in the '70s.
Had some basic problems.
1) the speaker cone is imperfectly coupled to the air.
2) The sensors that I could hook to the speakers were
imperfectly coupled to the speaker. Probably could do a lot better
with a speaker designed with a sensor in mind.
3) I was trying to cover too much frequency range with the woofer.

Turns out you can go a long way by tailoring the output impedance of the
amp to the loaded impedance of the speaker. That meant a negative
amplifier output impedance.

Experiments with better coupling between the speaker and air resulted in
purchasing a pair of Klipsch Corner Horns. At that point, getting more
bass seemed a moot point ;-)
mike

--
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
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MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/

 

[Chris Carlen]

Frank Bemelman wrote:

http://www.homestead.com/whaan/files/pagemfb.html

Still worth a fortune, in particular the 22RH532 if you can
find someone who wants to sell. I don't think Philips has
sold many, too expensive probably for the average guy.

Interesting. Thanks for the link.


Good day!



--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

 

[Tim Wescott]

bill.sloman@ieee.org wrote:

Chris Carlen wrote:

Greetings:

My recent experiences with motion control, coupled with an interest in
audio, have led me to the following question:

Why aren't speakers driven closed loop? Ie, have a position sensor on
the speaker diaphragm, and drive the speaker in a servo loop?

I realize this would be challenging particularly for tweaters (which
also don't necessarily exhibit "stiff" diaphragm movement), but the
concept is more of what I am interested in.

Has this been done? It would seem to be the "holy grail" to have the
speaker cones move in lockstep with the signal waveform.


It has been done - some years ago Philips used to sell loudspeakers
that worked on this principle. They weren't all that good, probably
because the position of the diaphragm is measured at one point, and the
diaphragm, not being infinitely rigid, distorts under load.

IIRR Philips used an accelerometer mounted on the drive coil as their
"position" sensor.

-------
Bill Sloman, Nijmegen

AFAIK it is currently being done with subwoofers.

Trying this with actual speakers would be very difficult because of
resonances and other transfer function effects in the speakers. If you
were shooting for a doctorate you could consider an adaptive system that
predistorts the drive going to the speaker to account for spectral and
nonlinear distortion, perhaps with microphone feedback. I suspect that
such a system would never be cheap enough for any but the highest-end
audio, and may never be better than the Philips system mentioned above.

--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Paul Hovnanian]

Frank Bemelman wrote:

bill.sloman@ieee.org> schreef in bericht
news:1118162730.230120.327060@g44g2000cwa.googlegroups.com...


Chris Carlen wrote:
Greetings:

My recent experiences with motion control, coupled with an interest in
audio, have led me to the following question:

Why aren't speakers driven closed loop? Ie, have a position sensor on
the speaker diaphragm, and drive the speaker in a servo loop?

I realize this would be challenging particularly for tweaters (which
also don't necessarily exhibit "stiff" diaphragm movement), but the
concept is more of what I am interested in.

Has this been done? It would seem to be the "holy grail" to have the
speaker cones move in lockstep with the signal waveform.

It has been done - some years ago Philips used to sell loudspeakers
that worked on this principle. They weren't all that good, probably
because the position of the diaphragm is measured at one point, and the
diaphragm, not being infinitely rigid, distorts under load.

They were incredibly good, and were capable of delivering an
enormous loud bass without distortion. In 1973 (?) I heard
this speakers for the first time. Of cource it was demonstrated
with a soundtrack containing large timpanis, and it was 2*LOUD*2
and it was incredible. For an extra dramatic effect, the
demonstration was with (thin) curtains in front, that were opened
shortly after an impressive intro of the demonstration.

Interesting. What sort of bass drive amplifiers were they using?
Compared to traditional systems, their 'open loop' gain must have been
pretty high.


--
Paul Hovnanian mailtoaul@Hovnanian.com
------------------------------------------------------------------
Very funny, Scotty. Now beam down my pants!

 

[Kalman Rubinson]

On Tue, 7 Jun 2005 20:42:20 +0200, "Frank Bemelman"
<f.bemelmanq@xs4all.invalid.nl> wrote:

Still worth a fortune, in particular the 22RH532 if you can
find someone who wants to sell. I don't think Philips has
sold many, too expensive probably for the average guy.

Only two weeks ago, I came upon a tag sale with lots of
old audio stuff including some 3panel Magnepans, Hafler amps, a
Tandberg cassette deck, many(!) tapes and mikes and, among the myriad
of speaker boxes, a set of Philips powered MFB speakers.
Unfortunately, all the stuff looked dusty and grimy as if cats had
been pissing on them for years. Too bad.

Kal

 

[Frank Bemelman]

"Paul Hovnanian" <Paul@Hovnanian.com> schreef in bericht
news:42A60898.86727D8@Hovnanian.com...

Frank Bemelman wrote:

They were incredibly good, and were capable of delivering an
enormous loud bass without distortion. In 1973 (?) I heard
this speakers for the first time. Of cource it was demonstrated
with a soundtrack containing large timpanis, and it was 2*LOUD*2
and it was incredible. For an extra dramatic effect, the
demonstration was with (thin) curtains in front, that were opened
shortly after an impressive intro of the demonstration.

Interesting. What sort of bass drive amplifiers were they using?
Compared to traditional systems, their 'open loop' gain must have been
pretty high.

I don't know. Here's the schematic:
http://www.mfbfreaks.nl/Service532.pdf


--
Thanks, Frank.
(remove 'q' and 'invalid' when replying by email)

 

[Mark]

On Tue, 07 Jun 2005 19:44:48 +0200, Mark <Mark@> wrote:

On Tue, 07 Jun 2005 13:10:47 -0400, Mike Monett <no@spam.com> wrote:

bill.sloman@ieee.org wrote:

[...]

It has been done - some years ago Philips used to sell loudspeakers
that worked on this principle. They weren't all that good, probably
because the position of the diaphragm is measured at one point, and the
diaphragm, not being infinitely rigid, distorts under load.

IIRR Philips used an accelerometer mounted on the drive coil as their
"position" sensor.

Bill Sloman, Nijmegen

Bill,

You triggered an old memory of a feedback winding adjacent to the main
coil. While looking for it, I came across the following:

----------------------------------------------------------------------
Voigt, Not Black

Editor:

I was surprised to find Martin Colloms---and John Atkinson in his
footnote---perpetuating the notion that Harold Black "invented" feedback
(January '98, p.87). As I recently pointed out elsewhere (Hi-Fi World,
April 1997), that honor belongs to the British engineer Paul Voigt, a
pioneer of high fidelity, who had incorporated it in his Motional
Feedback Patent 231,972, dated January 29, 1924. Over 70 years later,
motional feedback as applied to loudspeakers has made little further
progress, and Voigt's use therein of selective negative feedback, which
he regarded as obvious and not worthy of special attention, is the first
reliably documented use of which I am aware---many years before the Black
disclosure. I enclose a copy of Voigt's circuit in the patent, and a
description of its operation in his own words that shows that he fully
understood its application. The latter is taken from papers in my
possession, typed and annotated by him in August 1970, and reads as
follows:

(read the rest at http://stereophile.com/reference/70/index7.html)

So it appears negative feedback occurred earlier than textbooks state,
and involved our favorite topic - hifi. This should have generated some
choice phrases for John's collection.

Mike Monett

I am sure there was an Elektor Circuit many many years ago that used a
negative feedback system.

Yep I was right, Elektor published a Negative Feedback system in their
1975 issue, the system was called "Sonant" and was on page 230 of
issue number two. Which proves my theory once again, that Elektor is
by far the best hobby/pro mag on the block. Which also goes to prove
what a sad twat I am.

 

[Chris Carlen]

mike wrote:

I did a bunch of experiments back in the '70s.
Had some basic problems.
1) the speaker cone is imperfectly coupled to the air.
2) The sensors that I could hook to the speakers were
imperfectly coupled to the speaker. Probably could do a lot better
with a speaker designed with a sensor in mind.
3) I was trying to cover too much frequency range with the woofer.

Turns out you can go a long way by tailoring the output impedance of the
amp to the loaded impedance of the speaker. That meant a negative
amplifier output impedance.

Experiments with better coupling between the speaker and air resulted in
purchasing a pair of Klipsch Corner Horns. At that point, getting more
bass seemed a moot point ;-)

Yes, horns are the ultimate if one has the space.


--
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
crcarleRemoveThis@BOGUSsandia.gov
NOTE, delete texts: "RemoveThis" and "BOGUS" from email address to reply.

 

[John Popelish]

Chris Carlen wrote:

Greetings:

My recent experiences with motion control, coupled with an interest in
audio, have led me to the following question:

Why aren't speakers driven closed loop? Ie, have a position sensor on
the speaker diaphragm, and drive the speaker in a servo loop?

I realize this would be challenging particularly for tweaters (which
also don't necessarily exhibit "stiff" diaphragm movement), but the
concept is more of what I am interested in.

Has this been done? It would seem to be the "holy grail" to have the
speaker cones move in lockstep with the signal waveform.

The biggest problem with this approach is that, above self resonance
(where most of the energy is pumped into a speaker) it is an force or
velocity device, not a position device. That is, the force applied to
the mass of the speaker (and the considerable mass of the air in front
of it) is proportional to the current delivered to the speaker. So
there is a considerable phase shift between the speaker current and
the position of the cone, as well as an integrator type frequency
response (reduced excursion at higher frequencies for similar
current). So any servo type of drive has to take that into
consideration. It is the pressure (fluid force) that is ideally close
to being in lockstep with the driving waveform, not the position.

Of course, a close microphone could provide nearly real time pressure
feedback.

 

[John Larkin]

On Tue, 07 Jun 2005 15:55:24 -0700, Chris Carlen
<crcarleRemoveThis@BOGUSsandia.gov> wrote:

mike wrote:
I did a bunch of experiments back in the '70s.
Had some basic problems.
1) the speaker cone is imperfectly coupled to the air.
2) The sensors that I could hook to the speakers were
imperfectly coupled to the speaker. Probably could do a lot better
with a speaker designed with a sensor in mind.
3) I was trying to cover too much frequency range with the woofer.

Turns out you can go a long way by tailoring the output impedance of the
amp to the loaded impedance of the speaker. That meant a negative
amplifier output impedance.

Experiments with better coupling between the speaker and air resulted in
purchasing a pair of Klipsch Corner Horns. At that point, getting more
bass seemed a moot point ;-)


Yes, horns are the ultimate if one has the space.

You want horns?

http://www.scrounge.org/speak/burwen/

Richard Burwen did (maybe still does?) design Copley's switchmode
power amps, used for servos and shakers and MRI gradients and stuff.
He told me that for every new amp design he fills a bucket with blown
fets. He did a chapter in Jim Williams' first book.


John

 

[Mike Monett]

Kevin Aylward wrote:

[...]

It occurred way before then. To wit, steam engines had a governor to
regulate speed.

Kevin Aylward

That's mechanical.

Mike Monett

 

[Boris Mohar]

On Tue, 07 Jun 2005 17:24:28 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

You want horns?

http://www.scrounge.org/speak/burwen/

John

You call those horns? That is a whole house heating system. If you want
real horns you'll need a shovel

http://www.royaldevice.com/custom.htm (Scroll down)




Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

 

[artie]

In article <d84gbm01bfc@news2.newsguy.com>, Chris Carlen
<crcarleRemoveThis@BOGUSsandia.gov> wrote:

Greetings:

My recent experiences with motion control, coupled with an interest in
audio, have led me to the following question:

Why aren't speakers driven closed loop? Ie, have a position sensor on
the speaker diaphragm, and drive the speaker in a servo loop?

I realize this would be challenging particularly for tweaters (which
also don't necessarily exhibit "stiff" diaphragm movement), but the
concept is more of what I am interested in.

Has this been done? It would seem to be the "holy grail" to have the
speaker cones move in lockstep with the signal waveform.


Just pondering.


Good day!

Hmmm... Infinity ServoStatik (spelling? in the 70's) used
electrostatic panels and a servo subwoofer.

--
Namaste--