A Stiff Breeze

Massless Speakers Part 3

Dr. D.M. Tombs, Gerald Shirley and the Corona Wind Loudspeaker, 1955

Dr. David M. Tombs was the designer of a corona wind loudspeaker (ion speaker) in the UK in 1955. This design was never patented or commercialised but was demonstrated at the Imperial College, London, and at the AES in New York.  An article by Tombs appeared in Nature in 1955 and Electronics in 1957.  No doubt inspired by earlier works and patents of the 1920s Tombs went on to develop, research and improve the device in detail.  It was the first widely demonstrated corona discharge based design.

Early in its development the American Gerald Shirley was involved in the project, focusing on trying to commercialise the design.  He authored a few more larger detailed articles in Radio and Television News (1956), the JAES (1957) and Radio-Electronics (1957).  However it never became a product for sale.

Gerald Shirley did get exclusive rights to the speaker for manufacture by his company Televex Co. in the US. Tombs had been involved in a wide variety of other technology developments before this and went on to pursue his career in a different direction (at Hoover) afterwards. Neither inventor patented the device. The book Acoustics and Vibrational Physics (1966) did feature a section on it as did Electroacoustics (1970).  For further technical information on it the paper by Matsuzawa 1973 is detailed about a speaker based on Tombs' design and the thesis by Sterba 1991 does further work.

Prototypes of these devices showed promise but also demonstrated some shortcomings. The smaller units were very quiet but did produce a full frequency range.  You would need to be quite close to the high voltages to listen, and being close also meant the background hiss was more obvious.  The main drawback of efficient ozone production was also very evident. Later larger units made by others (Pass, Iverson etc.) increased this and with increased size power consumption also went up dramatically.  Gerald Shirley's demo unit is known to have been disposed of later by accident, but there are some photos in his articles.

A corona wind loudspeaker
Tombs' Corona Wind Loudspeaker Prototype

The physical basis for this loudspeaker is the ion or corona wind effect.  It could be considered a true ionic or ion loudspeaker, as there is a corona discharge plasma produced (seen as tiny points of light on the electrodes) but the main effect is that of ions being driven through the air from a high voltage potential and colliding with air molecules.  A more recent study also suggests that electrons may have a direct effect (Nature 2018).  One of the primary promises of this technology over plasma is that it can be made to produce frequencies over the full audio spectrum.  It lends itself to using multiple points (or wires) to create more surface area and therefore can move more air allowing lower frequencies to be produced than plasma tweeters.  The major disadvantage would be ozone gas creation, for which it is very efficient.

Although not cited by Thomas Townsend Brown, his patent from 1960 (and later ones) is an identical description of Tombs' corona wind loudspeaker, including both the single ended and push-pull (triode) versions. Nothing beyond this and his similar patents were produced by Townsend Brown who was also good at hyperbole and misinterpreting experimental results (included for reference but not recommended reading).  Nelson Pass mentioned this, more on that later.

Around 1973 the audio designer John Gordon Iverson designed a prototype corona wind loudspeaker and he is quoted as referring to work from the 1950s on which it is based.  This "force field" loudspeaker didn't get beyond prototype and descriptions of it do describe a large panel version of a full range corona wind speaker.  Beyond Klein's plasma tweeter which bears no similarities, there was little else developed around the 1950s so it would seem that it was Tombs' work he found.  Another prototype forcefield speaker was developed at CIT in 1976 by Albert Von Schweikert, who later used the name for a non-massless speaker as well. As far as any technical information goes, an ion loudspeaker doesn't appear to be any good for deflecting photon torpedoes so it is unknown why the term "force field" was used.

Part 4 - Popular Plasma

How Old?
Actual Plasma
A Stiff Breeze
Popular Plasma
Don't Breathe
Future Thinking

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