Components listed here have been formally reviewed in Stereophile and have been found to be among the best available in each of four or five quality classes. Whether a component is listed in Class A or Class E, we highly recommend its purchase.

Each listing—in alphabetical order within classes—is followed by a brief description of the product’s sonic characteristics and a code indicating the Stereophile Volume and Issue in which that product’s report appeared. Thus the September 2010 issue is indicated as “Vol.33 No.9.”

The phenomenon of the "singing flame" has been known since the 19th century. Place electrodes either side of a flame and, if you apply a high enough audio-modulated voltage to those electrodes, the ionized particles in the flame will cause it to emit sound. (Search YouTube for "singing flame" and you'll find many examples.) This principle was developed into a practical loudspeaker in 1946 by a French inventor, Siegfried Klein, who confined an RF-modulated arc to a small quartz tube, coupled it to a horn, and called the resulting speaker the Ionophone. An intense radio-frequency electrical field ionizes the air between inner and outer electrodes to produce a distinctive, violet-tinged yellow flame in the quartz combustion chamber. When the RF field is modulated by the audio signal, this causes the almost massless ionized flame to expand and contract in what should be a perfectly pistonic manner.