Motion controlled loudspeaker

Probably not... PID control was invented to help people who sell PID controllers to people who use PID controllers and it's become sort of self replicating.

It's a development from PLC controllers through the realms of contactors through to RLRL logic which has reached state of the art with new graphical interfaces which operate through the parallel port.

These days we use PICS but you can only get access to the appropriate registers through proper demonstration of trustworthyness. This is information that you will not buy.

Winky Winky.

DNA

You can improve it a lot, but you can't eliminate all the problems. You can effectively increase the control of the voice coil (basically identical to decreasing the output impedance and increasing the coupling of the coil) considerably at low frequencies, though.

Remember your robotics lab servo is running well below 20 Hz. The higher the frequency you get, the closer to a cycle a given amount of delay in milliseconds is.

You can make feedback systems work pretty well at 20 Hz... Velodyne has done it on subwoofers since the 1980s, and the modern accelerometers sold for automotive air bags make it easier and cheaper than ever before. You can't make them work at 1 KHz because the delay is too severe.

--scott

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

But can't the delay be shortened using a controller? That is, if a steep slope is detected that the controller knows the driver will struggle to accurately reproduce due to it's sluggish response time, it can output a much steeper slope to ensure the coil accelerates faster?

--
Posted via a free Usenet account from http://www.teranews.com

those of us who on a daily basis command 30,000 positions per second out of moving mirror galvanometer scanners would like to know what we could replace our feedback sensors and PID with?

Steve Roberts

I do believe some of the new FPGA devices can do closed loop control in to the kHz range. Feed forward techniques may also be used to mitigate some of the delay issues.

Can't say if it's practical for this application yet.

Later...

Ron Capik

So you're saying this will only work with trusted signals from artists and engineers that are registered as being certifiable?

Later...

Ron Capik

No comment on position feedback, but John Popelish was wrong when he said that a speaker is a position device below resonance. He neglects the effect of back-EMF, which means that at a (close-to) constant voltage, the coil is a constant *velocity* device. Try it sometime with a broken woofer - remove the cone and apply a volt across the coil. You'll see the coil rises at a fixed rate. I've done this with 4" voice coils from an ancient "washing machine" disk drive head mechanism, which makes the effect very visible.

Those of us who do not believe in the flakey definition of what part of P, I or D you need to change to get the answer you think you have would like you to define your interpretation of 30,000 positions per second.

DNA

But what if it changes? The controller can't see ahead in time... it has no way to anticipate the signal.

--scott

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

it can if each speaker driver includes a fixed delay, allowing the controller to effectively look ahead in time.

I looked at doing this a few years ago for the smps for an audio amplifier: add a 10-20ms delay, do a convex hull on the audio input (hull bounded by the smps frequency response) and dynamically adjust the smps output voltage to maximise efficiency.

Cheers Terry

Sure, join the IEEE and you might get it half price.

Winky Winky

DNA

Oooooooops. Mind you, be careful. There are rumours going on about advance fee frauds and some of these 'institutions' are about to catch a serious cold. Just make sure you tag on the extra 20% and it goes to the right party.

Sweet

DNA

The IEEE is a lot like a fraternity. You go through this initiation rite, and they give you a lapel pin and teach you a secret handshake called "Right Hand Rule."

--scott

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

No, John was correct. It's a velocity device AROUND resonance, where the back-EMF isn't masked by either stiffness or mass (lower Q means wider velocity region). Below that it's a displacement device.

LOL! Apply 1V or whatever you want on a speaker and look the cone pass through the window, troposphere, asteroid belt,...

--
Thanks,
Fred.

["Followup-To:" header set to sci.electronics.design.] On Wed, 11 Oct 2006 20:56:38 GMT, Genome wrote in Msg.

If memory serves me right, "PID control" was temporarily renamed "Fuzzy Logic" in the 90's.

robert

That's been tried. Just about everything has been tried.

The basic problem with direct radiating speakers is that from a cone motion standpoint they are like an integrator starting just above the frequency where cone mass provides most of the load on the voice coil. This "mass loading" starts just above resonance, or around 30-80 Hz for most speakers. It gets harder and harder to have a stable feedback system above this point.

Thing is, speakers are pretty linear in their mass-loaded region. So, feedback isn't going to help much, anyway.

Servo control has thus been pretty much restricted to subwoofers because it is feasible with them, and many of them can benefit from the linearizing effects of feedback.

The long term trend over the past 30 years has been to simply build loudspeaker drivers that are more linear at low frequencies and larger excursions. KISS.

Is that a reason to stop trying? I don't ask these questions because I think I've come up with a unique idea I ask them because it's valuable to know why something doesn't work; I think you've explained the pitfalls pretty succinctly, so thank you.

--
Posted via a free Usenet account from http://www.teranews.com

Most would say that they don't want to try something that has already already been tried by competent people who failed.

One relevant situation relates to a friend of mine who is moderatly well known in AES circles. He did a servo woofer for his undergraduate engineering project and it was fairly sucessful in terms of performance. It was based one of the most promising speakers of the day, the EV 30W. That came and went long ago. Just lately he designed some subs for his personal use. He went with some very long stroke drivers from the car audio world. No feedback, just feedforward frequency response compensation.