How Old - Massless loudspeakers

While others were wasting their time trying to make sound from electrical signals using solid, heavy, slow diaphragms there were a few pioneers who had the foresight to lay the foundations for the massless loudspeaker.

Without documented observations of the various related physical effects there would be no attempts to make sound from high voltage in the first place. In 1672, Otto von Guericke observed the corona discharge on pointed conductors. Francis Hauksbee in 1709 noted the electric wind from such a discharge. Later on even the bigger names in physics like Isaac Newton (1717) and Benjamin Franklin (1747) would note related effects from high voltage coronas. The electric fly from Benjamin Wilson (1750) would be one of the first physical demonstrations of the electric wind.

In 1777 Dr. Byron Higgins discovered and demonstrated that organ pipe-like tubes and glass jars could be used with hydrogen flame to produce sound and musical notes, tuned by the length of the pipe. This work on pyrophones or plasmaphones could be the first that would influence the later development of the massless speaker. A number of others experimented with similar technology. Michael Faraday in 1818 added further research and suggested the sound was created from very rapid explosions. In 1858 the American scientist John LeConte had noticed how the flame of gas lights could be influenced by musical sounds. John Tyndall, 1867, demonstrated a singing flame to the Royal Institution as part of 8 lectures. Henri De Parville included a large section in the book Les Causeries Scientifiques, 1862.

The idea that flame could be used to produce sound was first successfully exploited by Frederic Eugene Kastner, patented in 1873, with his Pyrophone. Using the natural resonance of small gas flames in varying lengths of glass pipe, an organ with one octave of notes was made. Kastner died before being able to make the most of his work.

With this early work providing a good grounding that linked sound with fire, the first devices that created sound from electric arcs were made. From earlier work by Hertha Ayrton on the noise of electric arcs (published later in 1902), William Du Bois Duddell (1899) in Britain created sound oscillations using DC electric arcs that would resonate given the right circumstances. Two effects were observed, the change in the sound of the arc when varying the supply voltage and more importantly how the arc could be made to oscillate at audio frequencies. Duddell patented this in 1900. This technology started to gain some public attention, there was even an article in the New York Times in 1901.

It is often quoted that Hermann Theodor Simon (1898) in Germany designed the same device as Duddell at a similar time if not before, as if they were in competition. This doesn't seem to be the case from the literature as they were approaching the subject from different angles and although there were similarities the two were distinct. Simon's work focused on how the arc could be modulated with a microphone and then an arc connected to a speaker (telephone) would pick up the signals - an early form of radio transmission. Duddell also discovered this effect by accident when others who were working on arc experiments found they were picking up the sound from his oscillator at a distance. That would be the main point of comparison, not that either were trying to invent an arc loudspeaker. Simon actually referred to his work as the "listening arc" and was not focused on making sound with the arc itself. Simon included one of Duddell's experiments in his 1911 book.

It has become very popular to cite Duddell as the inventor of the plasma speaker, or that more modern plasma speakers are a development of his "singing arc". Much as the device he discovered made sound and was an arc discharge it was primarily an oscillator, a way to create AC from DC power with the sound more of an interesting side effect. It was discovered rather than invented while Duddell was researching methods of damping the noise from arc lamps which Ayrton had been investigating in detail before. Despite some development with respect to audio, most notably from Andre Blondel (1903) and scientific demonstrations from Kohl in 1911, this was of far more use in the upcoming radio technology of the day. Valdemar Poulsen (1903) with his Poulsen Arc was amongst the first to exploit Simon's and Duddell's work for radio transmitters and it was a popular early method with work by many including DeForest patenting some improvements to Duddell's work in 1907. It was radio transmission that the technology found its best use in, not with loudspeakers. Modern massless speakers are typically based on corona and glow discharge plasmas and not the high current arc discharges used in the arc lamps that Simon and Duddell worked on.

If it was to be seen as a race to who "invented" the massless or plasma speaker then perhaps Lee De Forest has a claim as he drew a decent diagram of an arc being modulated by a microphone in his diary in 1897. It would seem that both the experimental apparatus and ideas around using arcs with sound were gaining ground in the scientific community during this period, driven by the discovery and invention for telephony and radio.

Thaddeus Cahill (1906) with the Telharmonium did use designs based on DeForest's and Duddell's work to create a musical device. This huge device used the arcs as audio frequency oscillators but still used early electromagnetic means to output the sound, not the arcs themselves. It was essentially the first synthesizer, but did not use the arcs as the speakers.

Around the same time as work around arcs was being done, so was work around the thermophone. This simple device used a fine wire heated by the audio signal and in turn heated the air to make sound. Key work by Peter De Lange from 1915 opened up the field for a wide number of patents by others as the race to make the best telephone receivers became a key driver. Perhaps not immediately considered massless, but the mass involved doesn't move - there may be thermal inertia to consider. Modern technology may still realize this technology as a product, e.g. Tao 2023, Torraca 2017.

A mention here of the Auxetophone that was also created around this time (1898) and often comes up. It wasn't truly massless as it was based on modulated compressed air, the modulation of which was achieved with a small diaphragm which was a much lower mass but still present.

It would be difficult to pinpoint the inventor of the massless speaker with respect to the most used glow discharge and corona discharge plasma speakers, but things really got going in the 1920s.

The first commercial application of a massless device was a microphone created with a corona discharge, patented for Tri-Ergon by Vogt, Engl and Massolle in 1921. As such the voltage was so low, 500V, and the gap so small (0.25mm) it would have barely generated a corona but it was enough. It was used to record sound for cinema and sold as the Kathodophone (Kathodofon) - not many sold and it was quickly surpassed by other designs.

A glow discharge plasma microphone was patented for Westinghouse by Phillips Thomas in 1925 but more interestingly this was followed by his first patent for a glow discharge plasma loudspeaker in 1927 (applied for 1922). This is the first embodiment of something resembling the plasma speakers we see today, where a glow discharge plasma in air is modulated to produce sound.

This was followed by patents from General Electric in 1927, "Improvements relating to electric sound-emitting devices or loud speakers". This really does well to explain what problems a massless speaker is addressing and describes one of the more basic mechanisms in clear and simple terms. Very unusual for a patent, especially in this field. It is the earliest description of a simple point to plane corona wind or ion loudspeaker, followed up a year later by a version based on a disc.

Many others contribute patents around this time, James Shrader (1926) with an ion speaker based on radioactive material, Lee De Forest with a corona coil in a parabola (1927), Lindenblad (RCA) in 1928 point to air speaker, Ramsey in 1928 having a horn loaded RF plasma loudspeaker, Lilienfeld 1929 with a charged disc controlling the air, Ruben in 1929 and 1930 with a horn loaded plasma and heated cathode ion speaker, Loewe in 1930 with a grid modulated ion speaker, Wolffe in 1930 with a multi-point ion speaker and De Forest in 1931 with a modulated gas flow speaker. These few with the GE patents describe almost all of the basic methods of "common" modern massless loudspeaker design.

There's no evidence that any of these devices, beyond the Kathodophone, came to anything commercial. That was soon to change.

Part 2 - Actual Plasma

Plasma Speaker and Tweeter Ionophone Information

Plasma Loudspeakers

Ionovac and Plasmatronic

Plasma Tweeters

Plasma Speaker

Corona Wind or Ionic and Ion Speakers