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The Termen Effect
There are so many fascinating
fundamentals of nature that come together in the simplicity of
heterodyne theremin design, Lev Sergeyevich Termen was chosen to make these discoveries!
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"Beyond 4 inches (10cm)
the belief hand
capacitance alone controls
the RF heterodyne theremin pitch is a factoid."
The hand-capacitance notion "has been" used as a simple
way to explain things!
"There
are true hand
capacitance controlled theremins in the digital realm, but they lack sensitivity to aerial
fingering and will require you to use your entire palm for
control."
Beyond 4 inches (10cm)
RF heterodyne theremin pitch variations are caused from changes in the
"radiation resistance".
This is the total RF electro-magnetic power radiated
from the pitch antenna divided by the square of the net current flowing into the
pitch antenna. The pitch field is a dual
electrical/magnetic equilibrium, not just a capacitive field
as so commonly state.
Here are some suggested reasons why
perfect
linearity develops.
Can pure hand-capacitance be
demonstrated as not always logical?
Make a $10 "Lev" LC tuned antenna and it will reveal that the note intervals of the higher octaves next to the antenna
can be made wider than
the low notes near the outside 18". This is in reverse of what
the pure hand-capacitance
logic would demonstrate.
The
"LC" tuner with a tightly
coiled tunable antenna coil design are the main features that
give you a
perfectly linear pitch field.
How many
linear octaves can be available for play?
This is determined by the amount of energy developed in
the pitch oscillator and "Radiated from the Antenna".
Three linear octaves is common but with good design over
five.
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Three components influence what is occurring around the pitch
antenna. These are inductance, capacitance and
resistance. In the "RF heterodyne theremin",
pitch change does occur by variations in pitch oscillator
capacitance but not from your hand acting like a capacitor
plate. It is the loading effect of your hand near the pitch
antenna which changes the capacitance reactance of the pitch
oscillator.
"Pure
hand
capacitance is involved in the RF heterodyne theremin
model but it does not work alone!"
Below talks about
your standard un-tuned theremin and then a uniquely tuned one.
The closer your hand is to
an un-tuned pitch antenna
of a heterodyne theremin the denser the available
radiating energy. The energy in the heterodyne theremin pitch field is
"extremely" low. The Thereminist neutral body
mass is a good "neutral reservoir" to absorb this energy
from the emanating RF
radiation. The theremin players hand/arm has less resistance
than the air space
and the forward pitch fingers absorb energy into your body
mass.
Your body's ability to
absorb a charge is demonstrated when you scuff your feet on the
carpet then get an electric shock when you touch the
kitchen faucet.
The heterodyne theremin must have a good earth ground, not
the Thereminist!
If the
theremin earth ground is poor you will hear distortion in the wave shape of
the RF heterodyne generated theremin tone. The theremin RF
relies on
weak ground currents and uses the
earth ground as part of the antenna system.
As the Thereminist hand approaches an un-tuned
pitch antenna, an
increase in the energy transfer
occurs which allows for an increase in the net current
flow into the antenna.
This decreases the "capacitance-reactance Xc" of the
L1 antenna side pitch oscillator.
This decreased capacitance-reactance has the same effect as
slightly increasing the capacitor value in the LC circuit of the pitch oscillator.
The frequency now goes lower as it feeds more current into the
pitch antenna. As
the pitch side oscillator goes lower the
theremin tone goes higher
as the pitch oscillator frequency
moves lower, away from the reference oscillator
frequency. The theremin tone is the difference of the two RF
oscillators, simple so far, eh?
In a tuned theremin pitch antenna the overall LC
tuning design "regulates" with perfect linearity, relative to a
musical scale, how much
energy radiates from the pitch
antenna into the theremin pitch field.
Heterodyne
theremin RF
energy transfers near the speed of Light.
"It
is an instantaneous change"
not really an energy flow.
Dual
LC oscillators that
are typically used in a RF heterodyne theremin, tuned to the same RF frequency
with their two coils in proximity will influence one another's wave
shape.
Very loosely coupled, the oscillators will lock into
synchronization. This creates the "Null Point" where no theremin sound is heard.
The Null Point is also the "zero point"
where the reactance Xc &
XL of both oscillators equal
zero when both their frequencies match. The
moment before the theremin locks onto the null point is where the theremin demonstrates its
maximum sensitivity. A well tuned RF heterodyne theremin
antenna can give a
response to your neutral body mass over two meters away or
lets say 6' to 8'. (This
distance is quite remarkable for such a low energy field, but not very useful for music.)
The RF heterodyne theremin's audio frequency (sound) is the diode detected
or mixed AM
frequency difference of the two
RF oscillators after breaking out of the Null Point.
This process of heterodyning or beating the oscillators and your interaction in
the theremin RF electro-magnetic pitch field creates:
The controlled
audible musical tones known as the "Termen Effect".
When perfect pitch linearity occurs
(LINKS)
it's Lev's gift for you. .
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