Speakers you can currently buy as a solid-state speaker or with a solid-state massless speaker built in:
Vaugn Loudspeakers’ Plasma Signature
Lansche Audio Corona
Acapella Ion TW-1
The plasma, corona and ion speakers in these designs are all the same type – but with completely different names!
Is a corona wind the same as an ion cloud? Could be, but maybe they are force fields as well.
Is my Ionofone like your Plasmasonic? Perhaps they both are like an Arc One.
Basic Definitions
Let’s start at some basics. An electroacoustic transducer, that which takes an electrical signal and converts it into sound waves (or vice versa), is called a loudspeaker. The word speaker is synonymous with loudspeaker – although older references may write ‘speaker as if shortening the word loudspeaker.
A conventional loudspeaker with a cone, coil and magnet is typically known as a dynamic speaker. An electrodynamic loudspeaker to use its full name, also electromagnetic, but these are less often used because everyone knows what a dynamic loudspeaker is. It is after all the most common type of speaker by far and as a result it is what most people know as a speaker or loudspeaker without going any further.
There are a small variety of other speakers that might be put into a category of “moving mass”. These can be related to the dynamic speaker but have different names to distinguish them from the cone/coil/magnet construction. They are often electrodynamic but have names such as ribbon, balanced armature, air motion transformer (AMT), planar magnetic, orthodynamic, isodynamic, magnetostatic, distributed mode (DML), MEMS etc. In addition to dynamic moving mass speakers there are most notably the electrostatic, piezo ceramic and magnetostrictive types.
There has been little regulation or standardisation of naming as they typically get named by the inventors, related to marketing names, what they are made of or the physics employed. However, in general most of those names describe their specific technology.
When it comes to the technologies without a solid moving mass, they don’t often get discussed en-mass, but in this case we could use the term solid-state. Although solid-state is commonly used to refer to semiconductor technology where it has replaced valves, it is also used with electronics that have no moving parts and so we will use it here. It is less contentious than the word massless (which website is this?!), as in physics these speakers will still have some mass even if it is negligible or relatively the same as the mass being driven.
Solid-state
So in the solid-state loudspeaker category there are two distinct types.
The easier defined one is the thermodynamic type – the heat of a mass (perhaps a wire) is varied and this varies the temperature of the air around it causing it to expand/contract. So although a solid mass is involved the heat of the air is the active part of the speaker. Yes the solid may expand/contract a little but that is not the active mechanism creating the sound. These are easily referred to as thermal speakers.
The second category is the electrohydrodynamic (or electro fluid dynamic or electro-aerodynamic) and has three subcategories or types and here is the point of this article:
Type one – a speaker that uses a plasma arc discharge to create sound.
Type two – a speaker that uses a corona discharge to create sound.
Type three – a speaker that uses a flame controlled by a high voltage to create sound.
So there we have the plasma, corona and flame speakers. Simple!
NO.
All of these three types use plasma, ions, electrons and flame in varying amounts with varying physics principles being employed. Over the last 120 years many names have been used to describe them and these have overlapped considerably and have been used interchangeably.
Principles
I shall try to distinguish the three types based on the physics at work. Some of the physics involved can be more complex but I have tried to reduce it to the basic principles.
Type one – an arc is created in the air. This is typically a high voltage plasma arc, but could be a low voltage high current arc. Sometimes the plasma is created between two electrodes, sometimes at higher voltages from one. It can be modulated in a number of ways and a number of different methods of supplying the high voltage can be used. In all cases a distinct area of glowing plasma can be seen. Plasma is ionised gas. The ions (electrically charged atoms or particles) and electrons in the plasma both create it and allow electricity to flow through it. Plasma is very hot, heating the air around it. If the intensity of the plasma is varied, e.g. at audio frequencies, the air around it varies in temperature which in turn causes it to expand/contract at the audio frequencies creating sound.
Type two – an electrical corona discharge is created on sharp electrodes. When a high voltage is present on a sharp point, on a sharp edge or a fine wire the electrons will fly off it creating a corona discharge. The tip or edge will faintly glow with a corona (a class of plasma), only visible in low light. If presented with a nearby ground point the electrons and ions charged by the electrons will flow through the air to that point, this effect is likely dominated by the electrons. As they do so they collide with air molecules imparting motion. If you vary the high voltage supply or modulate the ground with a grid the resulting air speed will vary. If you do that at audio frequencies it produces sound.
Type three – a flame is produced, typically by burning a supply of gas. A flame partially contains plasma. If electrodes are placed in or around the flame and a high voltage supply to the electrodes modulated it will vary the intensity of the plasma in the flame. If you do this at audio frequencies the variation in the temperature of the flame causes the air around it to expand/contract creating sound.
So simply put, type one you see a plasma, type two you don’t and type three you see a flame.
To take the easier third type first this is the least common. In the recorded cases of them being created they are most often referred to as flame speakers. Rarely they have been included as a plasma speaker and could be also known as a pyro-speaker.
The Name
Type one and two are a mess. They have both been referred to as the following (at least) and any combination and not including brand names:
Plasma
Ion
Ionic
Corona
Ionophone
Plasma arc
Ion wind
Ion cloud
Corona wind
Corona discharge
Ion-plasma
Singing arc
Talking flame
Blue flame
Force field (!)
The most commonly used term over all is plasma speaker, or plasma arc speaker (loudspeaker). As they are most often a high frequency transducer the plasma tweeter or plasma arc tweeter is also common. This most closely describes type one, where there is a visible plasma. If that was the only term used for them, and perhaps it should be, then that would be fine.
Unfortunately even near it’s early conception this type of speaker was described as ionic and called an ionophone (ionofone, ionofane etc.). From then on the use of ions in the naming of type one was common. Yes plasma is an ionised gas and so it is not wholly inaccurate.
In comes the type two. This type has never seen a commercial product, just a few prototypes and demonstrations. It is rarely described as a plasma speaker, although it has been. Early on the term corona wind was used but most often now it can be referred to as ion wind, ion cloud or just ionic or corona. Electrostatic has on occasion been used as a description, but the basic mode of operation does not involve a charge at rest even though there may be some static charge on or around the discharge points.
Further to that, testing has revealed that in the type two it is electrons that are the predominant cause of the air flow making it an electric speaker and not very ionic. Electric just seems to be too vague a description though, aren’t all loudspeakers electric? Also the use of the word corona and/or discharge nowadays has quite a different meaning to most people.
A Solution?
So now we have two different types of loudspeaker with different mechanisms for creating sound using similar or the same names.
This doesn’t pose a problem in most peoples lives but it is in the remarkably narrow field of solid state speakers. “That’s a nice ion speaker.”, “It’s not, I think you’ll find it’s a plasma arc wind transducer.”
So I propose the following simple rules and naming:
If you can see the plasma, call it a plasma speaker.
Alternatives, plasma arc speaker.
If you can’t see any plasma, call it an ionic speaker.
Alternatives, ion speaker.
If you set something on fire to make it then it’s a flame speaker.
Alternatives, none.
