Air Speaker
A website devoted to massless loudspeakers  

plasma speaker chain

   

 

Types of Air Speaker

I use the term "air speaker" in this site as it encompasses all of the different types, including the more popular (if you could call something so rare that) plasma tweeter. Here I try and describe the different types of speaker possible without using conventional solid diaphragms.

It is difficult to strictly define some types of air speaker. Of the many articles I have read there are contradictory definitions throughout them all. Here I define what I mean when discussing the different types on this site.

Types of Electrical Discharge Usable for Air Loudspeakers

Corona Discharge

Also known as Corona Wind, Ion Wind and Ionic Loudspeakers.

A typically high voltage (high kVs) low current (uAs) form of discharge.

An arc is not quite formed, but a glow will be seen at the tips of pointed/wire electrodes and sometimes weakly between them.

Runs cooler as power is dissipated over a wider area.

The mechanism of sound output is by modulating the streams of ions that collide with air particles (the corona wind).

Plasma Discharge (or Glow Discharge)

Also known as Plasma Tweeter, Plasma Arc and Ion.

Still high voltage (low kVs), but lower than above and some current (mAs) - also created with RF.

A glowing plasma thread is visible linking the electrodes (or contained by an RF field). This can be several centimeters long. The plasma is very hot (5000C+) and the cathode will get hot.

The mechanism of sound output is that by modulating the plasma, the superheated air around it expands and contracts.

Arc Discharge

Also known as a plasma arc or carbon arc.

A low voltage (10s to 100s) high current (As) discharge.

A large but short arc is created. This is typically a very hot arc with hot electrodes, similar to the arc created when welding metals. Sound output is similar to the plasma discharge mechanism.

Flame

A real flame is produced by burning a gas.

This can then be modulated using electrical or magnetic means.

Categorising

If it is difficult to categorise a loudspeaker into corona (ionic) or plasma (glow discharge), try and understand which effect is predominent in making the sound.
Ions hitting air particles is corona.
A hot discharge superheating the air is plasma.

Hot or Cold Plasma?

From a physics perspective all of the plasmas involved in any air speaker are "cold" plasmas. This may seem strange when the temperature of the plasma may exceed 5000 degrees Celsius, but they are still known as cold as the ions in the plasma are cold compared to the hot electrons. "Hot" plasmas exist in very different environments such as the Sun, in which the ions and electrons are in thermal equilibrium. It's a small point, but it took a while to get to the bottom of the definition as different manufacturers or designers have claimed the plasmas in their designs to be hot or cold, according to the physics definition - they are all cold plasmas.