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Thursday, April 27, 2017
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Plasma Loudspeaker

A plasma loudspeaker is a transducer that produces sound by means of an ionized gas channel rather than the voice coil of a conventional loudspeaker. Plasma loudspeakers characteristically have a flat frequency response at the higher acoustic frequencies because of their "massless" membrane; however, their low-frequency response is limited.

In a normal loudspeaker design, the inertia of the driver will resist an instantaneous change in its position as the magnetic field varies with the input. This decreases the fidelity of the speaker, as the input is distorted due to the physical limitations of the device, particularly for strong high frequencies. In a plasma speaker, this limitation effectively does not exist, as the air itself is driven directly by expansion of the plasma as the current through it varies.

The plasma speaker design is a member of the family of so-called massless speakers.

A plasma arc loudspeaker or plasma-dynamic loudspeaker is a loudspeaker that creates sound by varying air pressure through a corona discharge or electric arc.
It is an evolution of William Duddell's "singing arc" of 1900 and, in recent times, modern research into spacecraft propulsion in the form of the ion thruster.

Plasma tweeters are claimed to be an improvement on traditional tweeter designs because the driver has very little mass, and so low inertia, reducing distortion and increasing transient response. Because of their inability to move large volumes of air, they are limited to reproducing only very high frequencies, and are therefore usable only as tweeters.
Most of those who have heard them claim they are notably sharp and clear.

more about Flyback driver

The TL494 works as an oscillator and a modulator, it generates a high frequency (5KHz to 45KHz) to drive the flyback transformer to make high voltage arcs.
Then the TL494 modulates the audio frequency into the main high frequency. Now the flyback transformer is being driven by the high frequency and the audio frequency, and when the arc is produced, the arc vibrates the air with both the audio and high frequency creating sounds.

The 10k potentiometer is used to change the TL494's internal oscillator frequency - from 5KHz to 50KHz.

With the 22k potentiometer you can change the volume.

Waterfall test: (a) Cronos Plasma Loudspeaker and (b) generic Moving Coil-type Speaker.

The main advantage of plasma loudspeakers is the absence of membrane and moving parts, which makes them essentially inertia-free. This results in a near-perfect transient response, i.e. the ability to instantaneously respond to an infinitesimally short pulse, and frequency response free of resonance.

The former allows creating acoustic generators that can produce very short impulses with wide spectrum, and the later allows creating acoustic generators with high fidelity output up to 150 kHz and higher. In addition, plasma speakers can be made very small in size and can work as true acoustic point-source with uniform directivity curve.

However, there are also some difficulties associated with plasma loudspeakers that limit their wide exploitation. The main problems are the following:
  • poor signal output at lower frequencies
  • ozone production as a byproduct of corona discharge
  • longevity of high curvature electrodes
  • low electric to kinetic transduction efficiency

Modulated Plasma Audio Transducer, Circuit Simplification with Power Bipolar Junction Transistors [pdf]

Very good information about Plasma Loudspeaker by Ulrich Haumann

Andrew Parsons from Hamilton , New Zealand

Joye's page with very usefull tips for building

Hackerbot Labs (Plasma Speaker with TL494)