Closing the loop

_-_-_Adam · 10th April 2010, 10:08 AM

Anyone ever heard of Control System theory being applied to Sound reproduction.

ie Position feedback on a speaker cone should be a pretty good indicator of the sound pressure waveform.

Feed this Cone position back into and amplifier so that the speaker cone position closely matches the input source waveform using closed loop control system.

This has to be the best method surely! after all it's been a success in the Control & Automation industry.

AKSA · 10th April 2010, 10:20 AM

Philips did it in the mid-seventies. Called it Motional Feedback.

Never took off for some reason, now lost in the mists of time.......

sakis · 10th April 2010, 12:30 PM

elektor had a similar article i think

mickeymoose · 10th April 2010, 01:02 PM

Philips did it in the mid-seventies. Called it Motional Feedback.

Should that not be Mullard to you?
I have a pair of thes speakers (8") free to anyone who is willing to pay for shipping.

event horizon · 01:27 PM

Linn use the same type of system on there more expensive speakers on the bass drivers. Until very recently Paradigm used motional feedback to control some of there subwoofers such as the servo 15

It's not dead, you just need to look for the stuff

There is a whole artical on building a closed box 15Hz subwoofer & MFB amp in Electronics World & Wireless World of February 1997

gaetan8888 · 11th April 2010, 01:42 AM

Hello

The Motional Feedback was presented on the may 2008 issue of the Hi-Fi Worldmagazine, as an historical article.

Bye

Gaetan

Joachim Gerhard · 11th April 2010, 01:52 AM

Bill Waslo did an article in AudioXpress.
I think you can still buy his modification of a Dayton subwoofer on their webpage.
It reduces distortion. Perfect frequency response can be got with simpler methods like the Linkwitz Tranform Circuit.
A friend of mine did a circuit with a microphone glued to the cone plus an accelerometer.
He claims that both methods have benefit and he combined them over varios aereas of the response. I do not know how it excatly works though.
Others like Backes und Müller use a sepeate coil in a magnet field to get the feedback signal. It can be seperated from the impedance information too.
Hawksford and Mills did an AES paper about that, that you can download from Prof.Hawskfords webpage at Essex University.

10th April 2010, 10:08 AM	#1
_-_-_Adam diyAudio Member Join Date: Jan 2010	Closing the loop Anyone ever heard of Control System theory being applied to Sound reproduction. ie Position feedback on a speaker cone should be a pretty good indicator of the sound pressure waveform. Feed this Cone position back into and amplifier so that the speaker cone position closely matches the input source waveform using closed loop control system. This has to be the best method surely! after all it's been a success in the Control & Automation industry.

10th April 2010, 10:20 AM	#2
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Philips did it in the mid-seventies. Called it Motional Feedback. Never took off for some reason, now lost in the mists of time....... __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

10th April 2010, 12:30 PM	#3
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	elektor had a similar article i think __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

10th April 2010, 01:19 PM	#5
event horizon diyAudio Member Join Date: Feb 2008 Location: East Midlands, England	Linn use the same type of system on there more expensive speakers on the bass drivers. Until very recently Paradigm used motional feedback to control some of there subwoofers such as the servo 15 It's not dead, you just need to look for the stuff There is a whole artical on building a closed box 15Hz subwoofer & MFB amp in Electronics World & Wireless World of February 1997 __________________ "Never let your morals prevent you from doing what is right!" Salvor Hardin Last edited by event horizon; 10th April 2010 at 01:27 PM.

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10th April 2010, 01:02 PM	#4
mickeymoose diyAudio Member Join Date: Nov 2008	Philips did it in the mid-seventies. Called it Motional Feedback. Should that not be Mullard to you? I have a pair of thes speakers (8") free to anyone who is willing to pay for shipping.

11th April 2010, 01:42 AM	#6
gaetan8888 diyAudio Member Join Date: Apr 2007	Hello The Motional Feedback was presented on the may 2008 issue of the Hi-Fi Worldmagazine, as an historical article. Bye Gaetan

11th April 2010, 01:52 AM	#7
Joachim Gerhard diyAudio Member Join Date: Mar 2009	Bill Waslo did an article in AudioXpress. I think you can still buy his modification of a Dayton subwoofer on their webpage. It reduces distortion. Perfect frequency response can be got with simpler methods like the Linkwitz Tranform Circuit. A friend of mine did a circuit with a microphone glued to the cone plus an accelerometer. He claims that both methods have benefit and he combined them over varios aereas of the response. I do not know how it excatly works though. Others like Backes und Müller use a sepeate coil in a magnet field to get the feedback signal. It can be seperated from the impedance information too. Hawksford and Mills did an AES paper about that, that you can download from Prof.Hawskfords webpage at Essex University.

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