A Beginners Guide to the Massless Loudspeaker: Plasma Speakers and Ionic Transducers
What is a "normal" loudspeaker?
When most people think of a loudspeaker they envision a solid cone diaphragm moving inside a box. Rightly so, this electromagnetic dynamic speaker is the most common form by far, used in everything from phones to cars to exotic hi-fi.
However, it’s not the only way to make sound from an electronic source. Anything else is a rarer technology as usually it is just not as flexible, convenient or cheap to manufacture as the dynamic driver.
These are typically the electrostatic, ribbon, magneplanar and EMT – discussed in the design section.
All of these still have one thing in common – a solid mass used as the piston to drive the air. The solid mass cannot move in the same way as the air, it is heavier and slower, and therefore it introduces distortion. This distortion can colour the sound and makes it less clear than the original recording.
So what are you talking about?
If you are the average consumer you really do not care. The dynamic loudspeaker does the job more than adequately when designed well. If you are being picky and wanted the lowest distortion possible then perhaps you would want to look at alternatives to a solid mass driver.
These alternatives could be grouped under the “massless” banner and instead of a solid mass making the sound, more exotic physics is used such as plasma and ionic based diaphragms. Relative to air, the medium in which you hear them, they are massless and therefore the mass of the diaphragm shouldn't add to the distortion.
There are a few niche practical uses for these but mostly a group of audio enthusiasts known as audiophiles would be the target audience. People who are seeking the purest sound reproduction to recreate the original performance. There are also some scientific and music studio uses.
What are plasmas and ions?
Plasma is the fourth state of matter after solid, liquid and gas – also known as an ionised gas. In this case it is usually created using a high voltage arc in air. The plasma glows as it is very hot. The heat can be varied with an electronic signal and creates sound from the changes in the expansion of air around it.
If you don’t quite create enough ions (electrically charged atoms and molecules) to ionize and create a plasma in the air you can use the ions (and electrons) themselves to move the air molecules. Varying the drive signal to that can create sound from the varying wind speed.
There are a number of ways of achieving the two main effects above, discussed in the design section.
In both of these cases there are no moving solid parts and the sound comes right out of the air. The plasma type lends itself to use as a tweeter for higher frequencies and the ionic type can cover the full frequency range. The plasma types tend to be a small point source and the ionic types a larger array of charged points or wires.
Why aren’t there many around?
There has been much less work done on these types of speakers over the years – if you look in the archive section here you will see that the attempts can be listed in a small table (search commercial and prototype). Compared to the almost unending variety of conventional dynamic designs this is a tiny number.
The methods of creating plasma and ionic speakers generally need high voltages creating a safety issue. In addition they can produce electrical interference and toxic gases. It is quite possible to work around these basic limitations but that does mean the cost of entry is much higher than a dynamic speaker both in monetary and experience terms.
Therefore they require more work on the amplifier and power supply with more exotic and more expensive components, along with mitigations for the above issues. There is much less information around about their construction and therefore it takes longer to design and build them from scratch.
So why bother?
This question is similar to why climb a mountain, perhaps because it is there. With enough research and development this type of loudspeaker, while never being commonplace, may become a practical alternative to the other methods and perhaps be able to demonstrate some effects that the others cannot.
I would now recommend taking a look at the History section as it takes you through the early work through to the modern day developments in the field.
