The Plasmasonic headphone

Introduction :

The Plasmasonic headphone was the first ever made system able to reproduce the full acoustic frequency range with absolutely no moving or vibrating part. The system was composed of two main parts, the headphone itself and the servitude power box.

The main Box :

The main box (click to enlarge)

The main box was necessary to produce the high voltage very low current voltages that are needed to feed the corona discharges and the high voltage power amplifier build in the headphone side (see below). A small audio preamplifier and a volume control are also implemented in the main box.

Front side (click to enlarge) Back side (click to enlarge)

The headphone :

The headphone (click to enlarge)

The headphone includes the corona push-pull cell and the high voltage amplifiers.

One headphone cell (click to enlarge)

High voltage amplifier (click to enlarge)

Plasma cell (External side) Plasma cell (Internal side)

External side without the protection grid Internal side without the protection grid

Performances :

Before to realise the cascade scheme with three transistor we first tried a single high voltage transistor with the following results.

The amplifier frequency response with a single high voltage transistor (BU226)

With this transistor the maximum voltage modulation was only 1500 V moreover the transistor was quite big and too much powerful for the needs we had. So we tried assemblies of lower voltage small transistors. Below the performances with a two transistors system and a 2000 V modulation. With the final assembly of three transistors we were able to reach 3000 V modulation with a 20Hz to 20kHz bandwidth.

A two small transistors amplifier frequency performance

The sound of the Plasmasonic headphone was very clear, this is confirmed by the acoustic frequency response below (measured with a Bruel & Kager professional sound equipment).

The acoustic frequency response (the level is around 100 dB)

Conclusion :

The Plasmasonic headphone was able to deliver a very flat frequency response with a very low distortion. The first hundred pieces were sold at a price around 2000 $. Shortly after the Audio Reference company went in bankruptcy and it was the end of this fantastic adventure.

The first loudspeaker prototype :

At the same period I started to built loudspeaker prototypes, the model measured below was a very simple one made of many small points (sawing needle type) separated by a few millimetres, the power amplifier was made with an electron vacuum tube.

Although this speaker was not very performing (very low efficiency and bad frequency response) it shows clearly that cold plasma loudspeakers were also able to reproduce low frequencies. the pressure obtained at one metre was around 90 dB but the power consumption was around 100 Watts. The response is not as flat as the headphone one for complex reasons. Among them a strong vortices structure between the points (the flow far far to be homogenous).

The first loudspeaker prototype frequency response