The Plasma Tweeter

1
The Plasma Tweeter
Colin Joye
Plasma Science and Fusion Center
Massachusetts Institute of Technology, Cambridge,
MA 02139, USA
What is a Plasma Tweeter?
Advantages, Concepts
Future Plans
Sound is generated by a high voltage corona
discharge. An audio signal causes this flame to
change size, creating sound waves!

• History
• Invented around 1955 by S. Klein.
• Sold in 1960s as Ionovac.
• Later produced by other companies, Magnat,
  Acapella.

• References
• Siegfried Kleins patents 2,768,246
• AudioXpress magazine, April 2003, Vol. 34,
  Issue 4, Build a Plasma Tweeter
• F. W. Peek, Dielectric Phenomena in High
  Voltage Engineering, 3rd Ed., McGraw-Hill Book
  Company, 1929
• A. Von Engle, Ionized Gases, Clarendon Press,
  1965
• http//www.plasmatweeter.de (Ulrich Haumann)
• http//www.ionAudio.net (Colin Joye)

The dome tweeter is too large for its small
wavelengths, leading to the beaming effect.
Circuit Operation
The Physics
Flame Properties
Basic circuit operation 1. Some disturbance
causes the current in the Tesla coil to shift
quickly, generating a voltage. 2. This voltage
is sensed by feedback and causes the 6KG6A tube
to direct more current away from the coil. The
feedback signal dies. 3. More current flows in
the coil, triggering the feedback - An oscillator
is born! The high voltage self-sustains a corona
discharge. 4. The amount of current deflected by
the 6KG6A tube is controlled by an audio signal,
altering the flame height quickly.
The Tesla Coil is chosen to have low capacitance,
low losses and high Q. The feedback driven
oscillator is necessary because the coil must
operate at its self-resonant frequency. This
resonant frequency drifts slightly as the flame
size changes, and must be above 3-5MHz to avoid
audible hiss.