Bob said:
I don't think there is such an animal, today. There have been a few plasma
loudspeakers sold. One of them was by Plasmatronics (in the early 80's,
iirc), however, they weren't "cold". It used an inert gas (helium, I
believe) to create 'fingers' of plasma. Each finger was about 3" long and
glowed bright blue. This was only for the upper midrange and highs, and the
need for a large tank of helium was a real pita, plus the low end was a
conventional dynamic speaker.
The device was born as an "ionophone"; a classmate in the '50's (Fuji
Oda) built and evaluated one as his masters thesis around 1955.
He had to make the transducer itself from fused quartz because it ran
white hot (about a kilowatt of input power; as an RF carrier at 27 mHz.
The transducer shape was basically like an eyw cup with an electrode on
either side wall, connected dorectly to the output transmission line
from an RF transmitter. Amplitude modulation (AM) of the rf carrier
produced sound and some light from the plasma and hot quartz at the time
for that coonfiguration.
Ozone; yes.. smelled it often.
Plasma TV screens use a low pressure gas sealed in an envelope. The gas
glows when milliamps of current flow through it. The place where the
glow occurs is around the cathode or anode (I forget which) in the case
of DC current. If AC current is used, both glow alternately. Such gas
discharges are highly nonlinear; there being no current until breakdown
occurs, the abundant current and light. That's why an AC carrier, which
can be modulated at an audio rate, was used in the beginning.
The audio performance is entirey due to the expansion of the gas being
heated by the quantity of current flowing through it (I^2*R heating). On
an audio wave peak, the temperature and volume are greatest; on an audio
wave valley, the tempreature and volume are least. I think it is really
a clumsy way of productings ound, inherently nonlinear for moderate to
loud sound levels.
I was also fortunate enough to have seen and heard one that did not
(apparently) use an ignited plasma. It didn't play too loudly and was never
produced commercially.
That's what Fuji concluded.
It also created large amounts of ozone.
Yup.
It had
response down to dc. Its mode of operation was probably similar to those
plasma-based air cleaners. I've considered getting one of these air
cleaners, then apply the appropriate modulation, but I don't think it would
produce the type of sound that would sell (plus the ozone problem is still
there).
It's just a toy.
Ang. C.
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