Re: Speech sensors?

[Leigh Palmer <palmer@sfu.ca>]

> On Fri, 26 Dec 1997 23:56:36 -0800 Leigh Palmer <palmer@sfu.ca> writes:
> > > > > > I once tried it with a 5mW HeNe laser and a photocell to detect
> > > > > > reflections from a vibrating window glass.  It didn't work for me
> > > > > > but it might work with an optical system to concentrate the
> > > > > > reflected light on the photocell and sensitive amplifiers at  the
> > > receiving end.
>
> > What means did you use to detect the modulation? It seems to me that
> > one would have to look for some variant of an optical lever arrangement
> to
> > get a signal from the window membrane. Merely receiving the reflection
> > won't do the trick.
> > Leigh
> There should be a doppler effect as the window pane moves toward and then
> away from the observer.

Think about that. Does the sensor have frequency sesitivity at optical
frequencies? Are you using the edge of a nerrow-band filter? What
frequency sensitivity would you require to detect the Doppler effect?

I think that once you do these calculations you will find that the
setup you were using could not be expected to detect acoustical
vibrations of the windowpane.

Leigh