David VanHorn wrote:
>
> At 06:33 PM 7/29/01 -0400, Olin Lathrop wrote:
> > > It always mystified me why we drive a device that converts current into
> > > sound pressure, with a voltage waveform.
> >
> >I thought that too a long time ago -- until I tried it.  It didn't sound as
> >good.  Then I did some measurements and found the frequency response was
> >worse than when driven with a fixed voltage.  Then the obvious finally
> >became obvious to me as to why this is.
> >
> >True, the force pushing the center of the speaker cone is directly
> >proportional to current, not voltage.  However, you hear the result of the
> >displacment of the whole speaker cone, not the force applied to it.  The
> >mechanical system has relative resonances and dead spots a various
> >frequencies.  When a resonance occurs, the speaker's impedance goes up, and
> >the inverse happens at a dead spot.  With constant current drive, when the
> >impedance goes up, more power is delivered, thereby exaggerating these bumps
> >in the frequency response.  With a constant voltage drive, the power goes
> >down as the impedance goes up, which compensates a bit for the bumps.
> >
> >Sometimes the road less traveled is less traveled for a reason.
>
> Interesting.
> I must have lucked out with my speakers.


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

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu