Klein - Massless - plasma tweeter

There's a lot more material online about Dr. Siegfried Klein, rightly so, as he has contributed the most to the field of massless loudspeakers with two distinctly different commercial designs created over 5 decades. He was a prolific inventor and developer of massless tweeters from the '40s through to the '80s. Using ions in the brand name of his first tweeter, the Ionophone is a plasma tweeter as was the later Magnat MP range of tweeters. This made the term ionophone a popular one to describe plasma loudspeakers, although previously it was used for radio receivers and telephone speakers (Wireless World 1922 and Richard Engler patent 1923).

As mentioned, the earliest glow discharge plasma speaker in evidence is the patent from Dr. Phillips Thomas granted in 1927 which used a DC arc and differed considerably from Klein's design. Although an earlier patent on RF based plasma tweeters from George Ramsey (1928) shows that Klein wasn't the first to think of the idea, Klein's version of the plasma tweeter addressed many of the problems with that design. Klein was the first to produce a commercial plasma loudspeaker of any type. The earliest article from Klein was in L'Onde electrique in 1946, laying out the grounding for his first tweeter the Ionophone made by Audax (France) 1952, Plessey (UK) in 1954 and Telefunken (Germany) 1955 who helped improve the design, notably the electrode. The first reviews in 1952 from the same magazine and also Wireless World were both favourable. These had a round section horn loaded plasma, driven by a Tesla coil RF supply and valve (tube) circuitry.

Klein's own paper in Acta Acusitca in 1954 was followed by 3 patents (with more in other countries) in 1956 and 1958. He used these patents and intellectual property to license his designs for manufacture around the world by other companies. This revised Ionophone was named the Ionovac by DuKane's Ionavac division in the 60s and also manufactued by Electrovoice as the T-3500 in 1958 and Fane Acoustics Ionofane (and Ionofone depending on what you read) from 1960. The Ionofane was used by Bowers & Wilkins as the tweeter in their P2H loudspeaker and for a short period the P2H was licensed by Sony for sale in Japan. Even as late as 1974, a German company called Tecnac created an Ionofane clone.

These were all based on the same basic design of a slim rectangular section horn loaded quartz tube plasma generator and a valve based amplifier and RF biasing circuit. This was an all in one assembly intended to be incorporated into a larger loudspeaker that had conventional dynamic midrange and woofer drive units for the lower frequencies.

All of these were moderately successful with perhaps almost 2000 sold, especially considering that this was an expensive option for a tweeter. Klein did well to exploit the intellectual property and properly license the design out to other companies. This would be an ideal situation for an inventor who would like their invention to be manufactured around the world. It would seem that these tweeters were manufactured up to the late 60's before interest slowly petered out, there's likely only a limited market for such a design before the market gets saturated.

In 1978 Klein took a different approach in a couple of ways, with a different design and this time teaming up with just one company. This was also licensed for distribution in the USA in 1980 by Dahlquist Corp but they shelved it and customers there had to wait for Magnat USA to sell it years later in 1987. The Magnat MP range of tweeters (patented across 1980,81 and 84) while also based on an RF circuit had the plasma struck across open electrodes surrounded by a distinctive ball shaped grounded mesh. The mesh provided both a safe ground and RF shield. Early reviews suggest that ozone production was a problem. The substantial black block base encased a solid state circuit and was intended to be placed on top of an existing loudspeaker rather than built inside the case. L'Audiophile also gave this a positive review in 1980.

As the original Ionophone was created quite some time ago the patents and IP have been expired for a while. Vaugn Loudspeakers recreated the Ionovac in 2016, with revised modernised circuitry and is now on sale as part of their full range speaker.

Part 3 - A Stiff Breeze

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