Air Speaker
A website devoted to massless loudspeakers  

plasma speaker chain

   

 

Introduction to Air Speakers

What most people think of as a loudspeaker is known as a dynamic loudspeaker. This is typically a paper or plastic cone mounted on to a coil of wire which is suspended around a magnet. The audio signal is fed to the coil and this creates an alternating magnetic field that acts against the magnet. The cone then moves with the coil and pushes and pulls the air, creating sound. This is a very successful method of producing sound and probably accounts for at least 99.9% of loudspeakers in the world.

There are two other rarer methods used. Electrostatic loudspeakers use a thin metalised sheet suspended near a fixed grid. When a high voltage audio signal is applied to the grid the electrostatic charge pulls and pushes the sheet making sound. Ribbon loudspeakers use a thin ribbon of metal in front of a strong magnet. A high current audio signal is fed across the ribbon and it moves with the changing magnetic field of the ribbon, making sound.

All of the above have a common issue - they use a solid mass to drive the air. As a result of this there will always be some distortion present as the solid mass acts as a spring-mass-damper system and never truly follows the original signal. Dynamic speakers produce quite a lot of distortion, however good or expensive they get. The electrostatic and ribbon designs have lower distortion as the mass is lighter and tends to be driven across the whole diaphragm, but it is still there.

In an ideal world we would want to drive the air with the lightest medium possible and that is where the "massless" air speaker comes in - it makes sound using only the air itself, either converted to a plasma or driven directly by ions from high voltage sources.

These are actually one of the simplest possible forms of speaker, you need no more than a separated pair of wires with some correctly modulated high voltage across them to produce the sound. There are several different types of basic air speaker, which is why I keep using that term. I have discussed them in more depth here. And there are many different ways of creating sound with them, which I discuss here.

Briefly, the most common type is known as a plasma tweeter, and that is what you will usually see in youtube videos and DIY websites. A plasma arc is created between two electrodes and a basic radio circuit is used to create an audio modulated RF signal to drive it. As the plasma arc is quite small, it is difficult to produce low frequency sounds with any power and so these designs are usually made as tweeters - and very effective they can be as most commercial designs are based on this method.

There is also the corona wind method that can potentially create a wider range of frequencies as it usually uses a large number of electrodes to generate ions that collide and drive air particles (creating a wind). When this is modulated in a similar way to the plasma speaker the wind will oscillate and produce sound. There have been no commercial designs of this type, but there have been many built and documented - some very near to commercialisation.

Some designs are referred to as ionic loudspeakers. This name appears to cover both plasma and corona wind based devices so it can be a bit confusing to work out which actual principle is involved in creating the sound. Either way, these are all perfectly valid "massless" drivers, or at least drivers with a mass very close to that of air - which isn't very much I'm sure you will agree.

Hopefully you now know why you might want a speaker of this type, take a look at the rest of the site to find the numerous attempts that have been made to create them.

 

Adam Chambers