Currently, in the largely exclusive field of high-end audio, there is an ever-growing market for better quality audio transducers. These transducers have come in the form of normal dynamic cone speakers, electrocstatic sheet speakers, magnetic ribbon speakers, magnetoplanar speakers, flat-panel NXT speakers, and ion speakers. By far the most used speaker is the dynamic speaker, which uses a permanent magnet and electromagnet to create sound by way of a rigid cone. These dynamic speakers come in all sizes for woofers (low-frequency), mid-ranges (mid-frequency), and tweeters (high frequency). The largest problem with dynamic speakers, or any speaker, for that matter, is the weight of the cone. In a dynamic speaker, the electromagnet must quickly accelerate and deaccelerate the cone. This is not much of a problem in low-frequency drivers, but in many cases, it becomes the limiting factor to how well a high-frequency driver will sound. Electrostatics get around it a little by using a large sheet of extremely thin conductive plastic, kind of like Saran Wrap, but they have their limitations too. The same applies to magnetoplanars and ribbon tweeters, which use a very light weight metal element. The NXT speakers use a proprietary piezo-like film and heavy signal processing to create sound from complex surface vibrations. That leaves ion speakers.

     The Ionophone, also known as the Ionovac or IonoFane, was invented around 1946 by Siegfried Klein, makes use of the corona discharge effect to create sound from the air itself. Using the air as the sound emitting medium and also the sound transmitting medium means that there is no mass to move in order to create the sound. The corona simply heats the air very rapidly to produce nearly perfect sound. With no mass to accelerate, the ion speaker has theoretically perfect transient response- the ability to instantaneously respond to an infinitesimally short pulse. One problem which limits the usability of this method of creating sound it would require a very large volume of corona to produce low frequencies. Large corona means high voltage. Think of the power used by lightning bolt to create its tremendously low frequencies. An ionic device to create such low frequencies would likely be prohibitively impractical. But regular dynamic speakers handle low frequencies very well, so only mid- and high-frequency sound would really show a markable improvement by using an ion speaker.

     Besides the remarkable transient response of an ion tweeter, they have one other major advantage over any other type of tweeter: They are as near to a true point-source of sound as possible. This means that the sound emitted is equally dispersed in all directions, 360 degrees. No matter where you stand in a room with a pair of ion tweeters, you get the same clean sound. The stereo image does not change from one area of the room to another because the frequency spectrum is the same in all directions. Regular tweeters have optimal frequency spectra on axis. Once you move off of the axis, the frequency spectrum changes and the stereo image is degraded. Because the ion tweeters disperse sound 360 degrees, they require a larger amount of power to produce the same amount of sound as a dynamic tweeter. Ion tweeters can become quite loud if the room they are placed in is carefully designed to reflect some sound without causing echos. Early ion tweeters used a horn-shaped shroud to focus the sound in one direction (see Ionovac picture above, left). This horn increased the otherwise low volume output of the early ion tweeters, but also added multipath reflections which can cause sound fidelity degradation if the horn is not properly engineered. A properly engineered horn can have advantanges besides increasing loudness, namely extended low-frequency response. The top-most right photo shows an ion tweeter without a horn. By increasing the audio signal to the corona, the audio sound output level can reach very high levels on the order of 110dB or higher (measured near-field).