Motion controlled loudspeaker

David Grant · 2006-10-11T19:56:52+00:00

I was reading back on about the feasibility of a motion-controlled loudspeaker and found this cited as the main drawback:"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 orvelocity device, not a position device. That is, the force applied tothe mass of the speaker (and the considerable mass of the air in frontof it) is proportional to the current delivered to the speaker. Sothere is a considerable phase shift between the speaker current andthe position of the cone, as well as an integrator type frequencyresponse (reduced excursion at higher frequencies for similarcurrent)."(John Popelish)But wouldn't a PID controller address this? I seem to recall in robotics lab a similar dilemna: We had a 16" flexible ruler mounted cantilever-style to a servo shaft. Our input control signal was a square wave which was supposed to cause the tip of the ruler to move suddenly from position 1 to position 2 (some number of degrees away). Without the PID controller (open loop control) the response was out of phase and had horrible ringing, overshoot, etc... with it, it was vastly improved.-- Posted via a free Usenet account from

Oct 11, 2006 24 Replies

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Predictor 19 years ago

Fuzzy logic is used for more than mechanical control. See, for instance:

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-Will

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jasen 19 years ago

if you want an accelerometer that'll operate a high frequencies use a voice-coil and integrate the output.

Bye. Jasen

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Scott Dorsey 19 years ago

Some folks have tried this; there was even an article in a recent AudioXpress about using a dual-coil subwoofer off the shelf with one coil as a feedback winding.

The problem with this is that it's hard to avoid coupling between the two coils.

--scott

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

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prep 19 years ago

That's how the old Philips did it, 2 coils on the former, larger one to drive, small one for the FB signal.

Paul Repacholi 1 Crescent Rd., +61 (08) 9257-1001 Kalamunda. West Australia 6076 comp.os.vms,- The Older, Grumpier Slashdot Raw, Cooked or Well-done, it\'s all half baked. EPIC, The Architecture of the future, always has been, always will be.

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MooseFET 19 years ago

There was an article in the magazine "Power Conversion and Intelligent Motion" some years back where they made a sub woofer with a servo motor driving the cone. You may want to see if you can find the article.

The highest frequency at which the servo should have its gain cross over point is going to be lower than where the coil input to feedback signal gets to be 180 degrees. The "D" part of the PID controller will give you about 45 degrees of phase lead at the cross over.

There could be a problem if the signal frequency is a subharmonic of the gain cross over frequency. Distortion products can be increased at the gain crossover. If you imagine that the distortion is a signal added at some point within the loop, I think you will see why this is true.

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