The Once and Future Tweeter

Written by Bill Leebens

Back in the day, I had many an asthma attack induced by musty old magazines purchased at yard sales and flea markets. I loved car magazines, hi-fi mags, and especially those thick catch-all mags like Popular Science, Popular Mechanics and Mechanix Illustrated, which managed to cover cars, electronics, and all types of technologies from lawnmowers to nuclear reactors with a sensationalist flair and fast-and-loose grasp of physics that seems quaintly charming in retrospect. Looking at them now, I often feel an involuntary wistful smile come on while reading Tom McCahill’s road tests, in which he measured a car’s trunk capacity by loading in his bird dogs; or stories about home-built hovercrafts or airplanes; or pronouncements from now-long-dead physicists of how lasers would eliminate the threat of Soviet missiles, and so on. If you love swoopy post-war dream-cars and the outer space paintings of Chesley Bonestell, you’ve probably read more than a few of these mags.

The holy grail of those magazines were the stories in which a nerdy guy in a plaid shirt built something in his garage which rendered Learned Scientists Baffled!! and which seemingly Violates the Laws of Physics!! In the automotive world that meant zillion-mile-per-gallon carburetors made out of cast iron pipe and a drinking straw, or engines like the Bourke two-stroke, a tiny two-cylinder engine which Beats Detroit’s Beefiest V-8s!! while going Miles on a Tea-cup of Gas!! (unfortunately, it did neither—I wasted a lot of time in college researching it).

Perpetual motion machines abounded in those magazines, and the audio equivalent of a perpetual motion machine was (and is) the massless loudspeaker, which promises flawless reproduction by moving air without the nasty physical jiu-jitsu of cones, domes, and panels. You might have just now discovered plasma tweeters and the like…but it ain’t a new idea. Not by a long shot.

English physicist William Duddell examined the “singing arc”, an annoying tone produced by carbon arc lighting. Duddell discovered in 1899 that by varying the voltage to the arc, he could produce a variety of tones, creating a Victorian-era steampunk synthesizer.

Other mostly-massless sound-reproducers include Oscar Messter’s Auxtephones from 1903, which used modulated compressed air to terrify listeners and sorta reproduce music.  Along the same lines but even more terrifying was the flame loudspeaker built in the ‘60’s by engineers at transformer company UTC, while trying to simulate the sound of rocket exhaust. Their system used a McIntosh amplifier to drive the flame from an oxy-acetylene welding torch to reproduce Beethoven’s Fifth. —No, really—take a look here.

Getting back to those musty magazines, Hugo Gernsback was as responsible as any single individual for America’s enthusiasm for radio and electronics. His magazines may have featured prose that was a little caffeinated, but they were technically-solid and educational. The long-running Gernsback magazine Radio Electronics ran two articles in the November and December 1951 issues which had been translated from French, following their original appearance in Toute la Radio (“All Radio”).

The articles described the creation of French physicist Siegfried Klein, the “Ionophone”, a loudspeaker with no moving parts. The “Ionophone” was an ionization unit contained within a quartz horn-throat, coupled to a large, standard exponential horn. A platinum wire seated in the quartz horn acted as a cathode, and a 10-12,000 volt/400 kHz field is established between the wire and a cylindrical shield surrounding it. The field generates ions—charged particles— and thus heat. An insulated vacuum enclosure which surrounded the quartz horn-throat prevented conductive heat-loss and loss of charge. By modulating the 400 kHz field at audio frequencies, sound was produced…along with UV and heat.

At this point, the prose becomes as purple as the plasma of the Ionophone. A frequency-response graph indicated relatively flat response of +/- 5db from 25-10,000 Hz; the text stated that the speaker could reach “much higher frequencies…however, its output diminishes in the supersonic range.” The articles concluded with the description of a future filled with massless loudspeakers directly coupled to radios, and stated, “the (unidentified) biggest French manufacturer of loudspeakers is tooling up for mass production of Ionophones.”

Sixty-five years later, it’s pretty clear that such never occurred. However, Klein did license his technology in the ‘50’s and 60’s to the DuKane company in America (and through them, to ElectroVoice) and to Fane in England. DuKane made a tweeter unit known as the Ionovac; Fane’s version was called the IonoFane (and was utilized in an early Bowers & Wilkins speaker system). The Stereo/HiFi Directory in 1962 (and 1964, the only issues I have) listed the add-on Ionovac tweeter as $69.00 each, including power supply and crossover (about $550 today); other models ranged from $79.50 each (the tweeter housed in a small enclosure) to full-range systems including the Ionovac tweeter for as much as $246.00 each. Response was said to extend from 3.5-20 kHz, with no mention of the flatness of response.

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Interestingly enough, that 1962 Stereo/HiFi Directory featured some pretty advanced speaker technology. Just before the Ionovac listings was the Kelly ribbon tweeter from the UK, marketed by Irving M. Fried under the brand IMF; after the Ionovac listings came Janszen electrostatic models, both add-ons and hybrid systems. Modern-day listings might look a trifle tame, in comparison.

Since the early ‘60’s, a number of companies have made, or attempted to make, massless/plasma loudspeakers. Klein himself developed a spherical ionic tweeter for the German company Magnat; that driver had a large and imposing flame structure, and despite the presence of a platinum screen that was supposed to act as a catalytic converter, was said to produce nasty amounts of ozone. Ozone is always a potential byproduct of a large plasma; the legendary Hill Plasmatronics dealt with ozone by piping in helium from a large tank! Given its Frankensteinian appearance and impracticality, it’s not surprising that only 50 pair were built, each pair supposedly sold at a loss, despite the hefty price ($7,000-$10,000 during the product’s lifetime, about $23-$25,000 today).

In the ‘80’s, the large and imposing French Tolteque plasma loudspeakers appeared at shows; I can’t even find a photograph, or state with certainty if they ever reached production. No less an eminence than Nelson Pass tried building a variant of the plasma speaker known as a corona wind speaker; Pass used electrode grids from copy machines. The device worked after a fashion, and was even shown on the cover of Stereophile (Vol. 6, No. 1). Unfortunately, it also produced large amounts of ozone, which caused some respiratory issues for Pass, who shelved the project.

A German named Otto Braun produced a plasma tweeter called the Corona Acoustic; subsequently, the design was sold to Lansche in Germany, who produces systems using the tweeter. Acapella in Germany also has a tweeter based upon the Braun design (which may or may not be the same as the Lansche unit).

Going full circle: Jim Jordan, designer of  Vaughn Loudspeakers, is now replicating the DuKane Ionovac tweeter.  Jim told me that he’s had molds made for the horn, and is producing new quartz cells and porcelain couplers, and has designed a new power supply. The Vaughn Plasma Signature speakers were recently shown at RMAF with electronics from Wavelength, and Stereophile’s Herb Reichert— a man known for enthusiasm, but not overstatement—wrote, “…it might be the best sound at any show, ever.”


The Plasma Signature model from Vaughn Loudspeakers, using their replica DuKane Ionovac tweeter. Photo: Lee Scoggins/Part-Time Audiophile, Vaughn/Wavelength room, RMAF 2016.

Given the advancements in materials science that have appeared during the 65 years since Klein’s papers, I have no doubt that we will continue to see further improvements and developments in massless tweeters. I can’t wait.

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