Motion controlled loudspeaker

[[email protected]]

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

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.

 

[MooseFET]

I was reading back on rec.audio.pro 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 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)."

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.