Welcome to Roger Russell's Page
about the Ionophone Loudspeaker.
A History

Copyright 1996-2004 by Roger Russell
All rights reserved
No portion of this site may be reproduced in whole or in part
without written permission of the author.

 

The information on this page has been gathered from my personal experience, magazine articles, and reviews of the Ionophone. Any additions, corrections or comments are welcome. I will be happy to post information for anyone who can supply replacement quartz elements, electrode elements or other parts or information about the Ionovac.

 

Originally called the Ionophone, it was sold under the name of Ionovac by the DuKane Corporation, St. Charles, IL, Electro-Voice, Buchanan, MI and IonoFane by Fane Acoustics Ltd., Batley, Yorkshire, England.

That's on This Page?

General History and How It Works
The IonoFane
Ionovac Performance
Plessey Ionophone
Further research

 

Electrovoice T-3500 Information
Extending the Life of Quartz Elements
Hill Plasmatronics Speaker
References

 

Replacement elements now available at
http://www.ionovac.com

General History and How It Works

The idea of ionizing air particles and moving them with the influence of an electric field dates back to the late 1800's when Poulson demonstrated his singing arc. In 1900 Duddell also demonstrated a singing arc. It was not until 1946, however, that a French inventor by the name of Siegfried Klein (pictured at the right) thought of confining the arc to a small quartz tube and coupling it to a horn. He maintained that such an arc could be used for generation of subsonic or ultrasonic waves as well as a microphone or loudspeaker. It was called the Ionophone.

The principle is somewhat like an ideal speaker. No diaphragm is involved that has significant mass or suspension stiffness. There are no resonances or transient problems. Theoretically there is almost no limit to the frequency range and response is inherently very flat. With a large enough horn, response was thought to be able to cover the entire audio range and to well beyond 50kHz. A closeup view of the early ionization unit is shown at the left. The opening is facing down in the aluminum collar. A metal cathode then covers the quartz tube.

Klein also described an excellent source of ion production using an active anode of 50% precipitated platinum, 40% aluminum phosphate, 5% precipitated iridium and 5% graphite. This active anode was excellent for ion production. In Klein's original corona discharge model a separate filament heated the anode and modulation was superimposed on a potential of 700VDC.

A description of how this operates is by E. Aisberg, Publisher and M. Bonhomme, Chief Editor, both of Tout la Radio, in the December 1951 issue of Radio-Electronics. "A high voltage is set up between the outside cylindrical shielding and the platinum wire which is the axis of the emitter. Through the action of dielectric losses, the quartz surrounding the platinum wire reaches a temperature of 1,000 degrees within one or two minutes. The strong field, which is established between the platinum wire and the cylindrical shielding, produces emissions, which also produce heat in leaving the emitter, thereby assisting to maintain a high temperature. The heat is concentrated because the vacuum chamber of the evacuated quartz horn prevents its spread by conduction. Secondarily, the vacuum of this enclosure prevents the passage of electrical charges through the material.

Because of the concentrated effect of heat and the electrical discharge rich in ultraviolet radiation, the emitter releases a flow of ions. The high temperature in the neighborhood rarefies the air; consequently, the molecules are far enough apart to enable the ions leaving the cathode to follow a free course longer than they could in dense, cold air. It is nonetheless true that some air molecules are ionized by collision with ions and electrons coming from the emitter.

In short, we have before us a kind of capacitor whose plates are the coated emitter with its central platinum wire and the exterior shield. Between these plates there is a cloud of ionized particles, which are in a state of agitation because they are in an alternating field which acts on all bodies, whether positively or negatively charged.

If we change the strength of the alternating electric field, we also alter the amplitude of the individual oscillations of each of these bodies. Now, molecular movement and heat are two words to describe the same phenomenon. Therefore, by varying the strength of the electric field, we can obtain corresponding instantaneous variations of temperature.

Nothing is easier to the radioman than to vary the strength of a high frequency field at a low frequency rate. The inventor of the Ionophone simply modulated his high frequency field at audio frequencies. The temperature in the vicinity of the emitter was varied in proportion to the low frequency. This takes us back to Edison's original Thermophone, with the exception that where Edison's heated wire was limited to the lower audio frequencies, the Ionophone reproduces with equal exactitude all frequencies within the audio range. (The old Thermophone produced sound by expansion and contraction of the air surrounding a heated wire, which of course had considerable thermal lag.)

Each variation in temperature produces an expansion of air, followed by a contraction, thereby producing a sound wave. These sound waves spread along the length of the exponential horn without friction and manifest their presence by sounds of the strength, form and frequency desired."

In a later model the arc was generated by a 100kHz oscillator and then modulating it with the audio frequency. A platinum anode was located in the center of the quartz tube. This was connected to the high voltage terminal of a resonant coil at the output of the oscillator. By adding a small metal strip around the outside of the quartz tube, a blue glow discharge was caused inside the tube. When the oscillator was modulated by an audio signal, the sound could be heard from the horn that was coupled to it. There was a problem of audible hiss, however, that could be heard from the corona discharge. This was found to go away when the oscillator frequency was raised to at least 2 or 3MHz.

A few years later he was granted world patents. The first patent was number 2,768,246. Licenses were granted in several different countries: DuKane in the USA, Plessey Ltd. Of England, Telefunken of West Germany and Audax of France. Several problems were also overcome. One was that after a few hours of operation, the platinum vaporized and deposited on the walls of the quartz tube drawing the arc to a hot spot and reducing output.. Telefunken found that the use of a Kanthal electrode solved this problem. Kanthal is