I've seen a few servo driven subwoofer projects.  They're using a number of
different position sensors, but I haven't actually seen a laser detection
system.

Most of the successful ones use a linear actuator with a position sensor in
the drive.  I've seen a project with accelerometors glued to the voice
oil.  --Not sure about the success of that one.

My yamaha computer speaker system has a servo driven sub, although I'm not
sure about the measuring method.  Maybe I'll hafta take 'em apart.

Lots of projects come up under search for "servo subwoofer".  I haven't seen
anything to do higher frequencies --yet.  --Laser positioning might allow
that.
-Dal

----- Original Message -----
From: Roman Black <fastvid@EZY.NET.AU>

> I thought about doing closed-loop speakers, ie
> using a CD player laser or similar to measure
> cone travel, then using a high speed digital
> PWM to move the speaker cone to the precise
> position. More like a high speed voice coil servo
> than an analog speaker.
>
> Has anyone else done this or know anyone working
> on it??
> -Roman
>
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