Plasma speaker

Plasma speakers (sometimes called flame speakers if the source of the plasma is combustion rather than gas ionization) are a form of loudspeaker which vary the intensity of a plasma, rather than using a magnetic field to push or pull a conventional driver, to create compression waves in air (which a listener perceives as sound).

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. (This limitation is one of the reasons why tweeters are so much smaller than woofers.) 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. (Ionization of a gas causes its electrical resistance to drop significantly; see for example the "Jacob's ladder" for an explanation.)

Plasmatronics produced a commercial plasma speaker that used a helium tank to provide the ionization gas; other designs (some of which date to the 1950s) use combustion of natural gas or even candlesFact|date=February 2007 to produce a plasma, through which current is then passed as in the gas plasma designs (though combustion designs do not require the initial high-voltage to create the plasma).

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.

The operation of the speaker requires a continuous supply of ionizable gas. One model used helium; with the attendant problems of handling and refilling the gas cylinders. The plasma by-product, ozone, can reach hazardous levels in closed rooms. Due to their high cost, limited range, frequent maintenance requirements, and limited utility, they are rarely used in modern loudspeaker equipment, and are instead considered a novelty, perhaps with desirable aesthetic characteristics.

External links

* [ The Audio Circuit] A site tracking, among other things, past and present brands of ionic speakers.
* [ The Art of Speaker Design]
* [ A loudspeaker with a plasma ion tweeter]
* [ An inspiring attempt at a working DIY plasma loudspeaker - well worth watching]
* [ William Du Bois Duddell and the "Singing Arc"]
* [ The Plasma Speaker Homepage]
* [ History]
* [ May 1968 Popular Electronics "Flame Amplification"]

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