How does it work?
The sound is produced by the interaction of
two radio frequency oscillators which normally are operating above the range
of human hearing. However, if one of these oscillators is slightly detuned
by varying it's frequency while the other oscillator remains fixed, the
difference in the frequencies (known as the beat frequency) is in the audible
range and can be amplified. This process is known as heterodyning.
The vertical pitch antenna controls the variable
oscillator. The electromagnetic field which surrounds the pitch antenna can
be changed by the proximity of the human hand, body, or other object placed
within proximity of the pitch antenna. The human body possesses a stored
electrical charge, which is called its capacitance. This body capacitance
can disrupt the electromagnetic field of the pitch antenna, thus affecting
the variable oscillator. The closer the hand gets to the antenna, the greater
the effect, and, therefore, the higher the beat frequency and the higher
the pitch. The farther the hand gets away from the antenna, the less effect
of the body capacitance, and, therefore, a lower beat frequency and lower
The pitch range (tessatura) can be adjusted
for four, five, or sometimes more octaves. In addition the pitch can be tuned
to allow for variations in playing distance from the pitch antenna (and thus
the physical space between pitches) by increasing or decreasing it's sensitivity
to body capacitance.
The horizontal volume antenna, which is in
the shape of a loop, also controls a high frequency oscillator, which when
detuned by the proximity of the player's hand capacitance, lowers the sound
volume. Moving the hand away from the volume antenna raises the volume. Carefully
controlled up-and-down movement of the left hand (although the antennas may
be reversed for left-handed thereminists) helps in the articulation of discrete
notes as well as playing dynamics, crescendos, decrescendos, etc.