|
The Plasma Tweeter
Colin Joye
Massachusetts Institute of Technology
What
is a “Plasma Tweeter?”
The
sound is generated by a high voltage Corona
Discharge. An audio signal
causes the size of this electric flame to change rapidly, creating elastic
sound waves!
Advantages
& Concepts:
The flame has no practical mass, which implies a
perfect transient response and acoustical impedance matching.
It also has no directional preference, and thus acts like an
omnidirectional acoustic point source!
The lower frequency response limit is set by the
flame size and is around 2 kHz here as shown.
The upper limit is in the MHz!
Circuit
Operation:
A
feedback-driven oscillator passes a current though a Tesla-like coil at its
natural resonant frequency to generate high voltage.
The
audio signal controls the amount of this current changing in the coil,
altering the flame size.
The coil is basically a parallel resonant circuit; high Q, low
capacitance and low losses are desirable. |
Physics:
The
flame self-sustains as long as the voltage peaks above a critical electric
field.
For
high frequency oscillation (greater than 3 to 4 MHz), the ions cannot move
very far in a period and form a region of space charge. This perpetuates the
corona flame and keeps it quiet.
When
ions bombard the electrode, electrons are freed by secondary emission
(heating). This sustains the
corona and causes sputtering, limiting electrode life.
Thoriated tungsten was used in the Ionovac.
Future
Plans:
Increase
the flame size! How low can the
frequency response go? Increase
the power efficiency to make larger flames practical.
Linearize
the system as a whole. The flame
itself is surprisingly linear. I
didn’t do a very good job on the audio stages since I wanted to get the
concept working.
Experiment
with Helium gas, which should allow for high acoustic output.
References:
|
Siegfried
Klein’s patents: #2,768,246
AudioXpress
magazine, April 2003, Vol. 34, Issue 4, “Build a Plasma Tweeter”
F. W.
Peek, Dielectric Phenomena in High
Voltage Engineering, 3rd Ed.,
McGraw-Hill
Book Company, 1929.
A. Von
Engle, Ionized Gases, Clarendon
Press, 1965
http://www.plasmatweeter.de
(U.Haumann)
http://www.ionAudio.net
(Colin Joye)
download: plasma poster > Plasma
< |
|
Magnat Plasma
Technology 
>