Page 313 - Electromechanical Devices and Components Illustrated Sourcebook

Chapter 16 Electrostatics 275

high-voltage power supply and the input signal is fed through
Clean Air a step-up transformer. As a signal is applied to the input of the
Discharge transformer, the attractive and repulsive forces allow the
diaphragm to vibrate in direct relation to the input signal.
This, in turn, generates sound.
Fan Motor These speakers offer good efficiency and excellent sound
quality but because of their support equipment and internal
Air Flow voltages, they are typically rather expensive. They are gener-
ally used only in high-performance applications such as home
or studio applications. One application where this technology
performs exceptionally well is high-performance headphones.
Positive Removable
Plate (Collector) Negative Fixed Plate The headphones are very lightweight and can enclose the
(Emitter) entire ear, produceing extremely high quality sound.

High-Voltage Isolation
Air Input
Generally, when dealing with electrostatics, you are dealing
with high voltages. Low voltages simply do not provide
Pleated Filter enough potential to be useful. It is important to respect the
voltages involved and to provide proper isolation between the
High-Voltage energized equipment and its operators. Generally speaking,
DC Power Supply the cat doesn’t want to be shocked every time it brushes up
Figure 16-3 Electrostatic Ionizing Air Filter Schematic against your electrostatic air filter. In a more serious light,
most electrostatic equipment carries extremely high voltages
and if isolation is not designed and maintained properly the
result can be serious injury or death.
are then electrostatically attracted to the collector plate. The In one instance that I am aware of, a technician was issued
collector plate is removable so that it can be periodically a high-voltage probe so that he could troubleshoot the power
cleaned. supplies of a large vacuum deposition system. It turned out
that the probe had an internal crack through the insulator,
which protects the operator from high voltage. When the
Electrostatic Loudspeakers technician touched the first power supply output with the probe,
he was immediately electrocuted. It seems that on the previous
Figure 16-4 shows a schematic representation of an electro- day another technician had dropped the probe, and rather than
static loudspeaker system. The diaphragm requires a quality, discarding it or turning it on for inspection and requalification,

Step-Up Transformer

Metalized Diaphragm

Rear Electrode
Audio Signal Input

AC Input

High-Voltage
Front Electrode
DC Bias Supply
Insulating Spacers
Figure 16-4 Electrostatic Loudspeaker