I remember hearing about Bob Gunderson many years ago,
Well, at least in the seventies.  He was one of those people who
truly spurred the imagination.

        Yes, a match makes lots of noise if its light shines in
to a photo cell.  The Sun, on the other hand, really sounds very
quiet at frequencies we can hear when we listen in real time.
The pulsations are a very slow ebb and flow that take many
minutes per cycle.

        When I was a kid, I unscrewed the cap on a headphone and
tried a little experiment.  The headphone had a thin steel disk
for a diaphragm which was shiny and smooth like a mirror.  If I
fed audio in to the headphones, the uncovered diaphragm vibrated
just as it would if next to my ear, but instead, these vibrations
caused the Sun light to wiggle a bit.  If you held a photo cell
in the reflected beam, you could hear perfectly good sound.

        The Central Intelligence Agency has refined this same
concept a bit and they have been known to spy on people by
bouncing a laser beam off of a window pane and converting the
returned light to audio and thus be able to listen in on the
conversations in the room with the window pane serving as the
diaphragm.  If the laser is infrared, nobody is going to see the
little spot of light and the tiny vibrations in the glass can
make the return beam wiggle a lot over a distance.

        I don't really know how well that system works and if I
did, I couldn't tell anybody on this list, but I truly don't know
if it is a good system or not.

        When I used to work as an audio visual repair technician,
we would sometimes play around a bit with the sound optics on
projectors we were fixing.  You could hold your hand in front of
the lens and reflect some of the light back toward the
projector.  If it leaked in to the photo pickup, you heard a
noise like an airplane engine because movie projectors have a
rotating shutter that looks like a three-blade fan whose blades
are perfectly straight.  The shutter cuts off the light 72 times
per second or three times per frame.  This very bright light was
usually very easy to pick up on the sound system.

        We would also flip a piece of paper, film, or any other
thin object between the sound exciter lamp and the photo pickup
which was just next to the edge of the sound drum.  If the
electronics and optics were alive, you heard a loud thump or pop
in the speaker each time you blocked the exciter lamp.  You could
also usually hear a ping in the speaker when you lightly tapped
the exciter lamp because the filament would vibrate slightly.

        Finally, one could sometimes hear a little bit of the
picture sneaking in to the sound track of a film.  It was a
puttering sound like a gasoline engine idling and it would
sometimes get louder and softer as the picture changed.

        It was fascinating what you could hear at times.  By the
way, some of you might wonder if the exciter bulbs hummed.  They
sure did on some projectors.  Others had a DC power supply or an
RF-type power supply that fed a very high frequency to the lamp
so that it wouldn't whistle while it worked.  I think the old
Bell and Howell 399 AV of the late fifties used one of these RF
supplies.

        For those of you who have never looked at a sound film
projector, they have a projection lamp which shines through the
film with an extremely hot and bright light.  There is a much
smaller lamp that shines through the edge of the film where the
sound track is and that is the exciter lamp.

        As one who is almost totally blind, I wasn't much for
focusing or framing the projectors, but the mechanical problems
that messed up the picture usually did things that caused the
machine to make odd sounds or would cause the sound track to be
bad so when I got the sound good and the machine purring along,
the picture was usually fine.

        Those of you who think this is a digression from amateur
radio are probably right, but keep this in mind.  I was able to
get that job because I had messed around with electronics and
mechanical stuff since I was 5 or 6 years old and I was able to
show them I could fix things.  That is how most people get jobs
and I doubt I would have even had a chance if I hadn't been able
to show an understanding of how the stuff worked.  Whether I was
a good or bad technician is for others to decide, but parts of
that job were really fun.  I can't say that ham radio got me the
job, but it certainly didn't hurt.

Martin McCormick