1. A high-frequency loudspeaker in which the audio-frequency signal modulates the radio-frequency supply to an arc maintained in a quartz tube, and the resulting modulated wave acts directly on ionized air to create sound waves.
2. A loudspeaker that creates high-frequency audio signals that are used to modulate a radio-frequency signal to a quartz tube.

The modulated signal then acts directly on a sample of ionized air to produce sound.