The history of ionic devices that
create sound can be traced all the way back to 1899 with the "Singing
Arc," a musical instrument based on the antique carbon-arc lamps that were
used to light the streets of London. Physicist William Duddell was put to the
task of figuring out how to quite the noisy lamps and ended up creating an
instrument out of them when he found that varying the voltage to a lamp
caused the singing frequency to change.
Then, in 1946, Dr. Siegfried Klein
tried using the corona discharge to create sound. The invention worked.
Dr. Klein patented the invention under French patent number 1,041,790,
and US patent number 2,768,246. He experimented with different emitter
materials to find which would last the longest and sustain the flame
In 1954, work started on producing the ion tweeter with DuKane in the USA
as a commercial product, which first came out in 1956. The ion tweeters
were also sold in England, Germany, and France under names such as
IonoPhone, Ionovac, and IonoFane.
Much later, Dr. Klein came out with
several patents on other ion tweeter designs under patent numbers
4,306,120, 4,464,544, and 4,482,788. These patents were filed between
March 1980 and July 1982 (granted as late as November 1984). Two of
these patents did away with the horn-loading that was used on the early
tweeters and concentrated on 360-degree sound dispersion. Even these new
designs, however, used vacuum tubes extensively.
Finally, in 1993, Dr. Klein was able
to do away with the vacuum tube technology and create a working prototype
ion tweeter using only solid-state devices, which was put into production
by the German company MAGNAT under the model number MP-02. The design
used only Bipolar-Junction-Transistors (BJT's), and a multitude of
special size inductors and several variable capacitors. While this
design probably showed an improvement in wasted heat over the vacuum tube
design, it could have probably been improved further be using
high-current high-voltage Field-Effect-Transistors (FET's). Quite
possibly, Dr. Klein could not find suitable FET's at that time to work at
the high voltages present in such a system.
MAGNAT MP-02 Schematic
Today, many high-voltage and
high-current FET's are widely available. Such FET's even beat vacuum
tubes in terms of cost and availability. In terms of efficiency, there is
no contest between FET's and vacuum tubes. Some FET's have turn-on
resistances of well under 1 ohm, while a vacuum tube can typically drop
100 volts or more when "on". In order to maximize the efficiency, we will
explore Pulse Width Modulation (PWM) as a way of combining audio
frequencies to the high-voltage oscillator in our design.
http://www.obsolete.com/120_years/machines/arc/index.html. This site
contains vast information on all kinds of antique electronic instruments
though the decades, like the Theremin, Ondes Martenot, and Moog Synth.
http://sundial.sundial.net/~rogerr/ionovac.htm, 1996-2000. This page
contains a history of the Ionovac and several pictures of the originals.
There is also a section where the author puts an excerpt from an article
he co-wrote in 1961 describing fidelity testing he did on an Ionovac.
http://members.aol.com/uhaumann2/plasma/ion.htm. Ulrich Haumann's
web page was the source for the idea of two plasma
tweeter projects done by Colin Joye previous to this senior project in
1999 and 2000. Ulrich's page contains a DIY ion tweeter project as well
as a picture gallery and some history including his meeting Dr. Siegfried
Klein in person.