The US Patent for the Theremin (Page 1 of 3)

 This is the original US patent for the theremin from 1928, with text and associated diagrams, which are referred to throughout the text.

 Patented Feb. 28, 1928.
1,661,058
UNITED STATES PATENT OFFICE

LEON SERGEJEWITSCH THEREMIN, OF LENINGRAD, RUSSIA, ASSIGNOR TO THE FIRM
OF M. J. GOLDBERG UND SÖHNE, G.M.B.H., OF BERLIN. GERMANY

METHOD OF AND APPARATUS FOR THE GENERATION OF SOUND
Application filed December 5, 1925. Serial No. 73,529, and in Germany December 8, 1924

This invention relates to sound generating apparatus or instruments of the type embodying an electrical vibrating system. It aims to provide a novel method of and means for producing sounds in musical tones or notes of variable pitch, volume and timbre in realistic imitation of the human voice and various known musical instruments. One object of the invention is to provide a simple and inexpensive instrument capable of producing musical tones according to the method embodying the same, the pitch, volume and timbre of which sounds may be varied over a wide range, and with delicate graduations.

An instrument embodying the invention comprises a sound reproducer, such as a telephone receiver or loud-speaker, connected to an oscillating system adapted to be controlled or affected by an object or objects, such as the hands or fingers of an operator held in relative position in proximity to an element of the system. For example, an electrical oscillating system including oscillator tubes of the electro-ionic type may be employed, and the circuits of the system may be so correlated that the frequency or frequencies of the electrical oscillations will vary in accordance with the variations in the electrical capacity or other characteristic of the controlling circuit caused by the movements of external objects, such as an operators hand or fingers as above stated. The operator's hands, or the objects moved by him are not required to make physical contact with the instrument, but if the instrument is arranged to permit such contact, the generation or production and control of the sound is not effected directly thereby as is the case with the ordinary musical instruments.

In order to generate clear sound or musical tones, and permit ready control thereof, a plurality of oscillators are employed, having a frequency above the audible range but interacting with each other to produce interference or beat-notes of audible frequency. The frequency of one or more of the oscillators is controllable by the operator to produce beat-notes of the desired pitch. The apparatus in preferred form also embodies means for controlling the volume and timbre of the music.

The improved method and means of this invention for producing sound or musical tones possess great advantages over ordinary musical instruments of the prior art. Apart from the simplicity in construction and operation of an instrument embodying the invention It is capable of producing clear and pure musical tones in realistic imitation of a known instrument such as the violin for example, and may be so constructed that the characteristics of the sound or music produced thereby may be changed as desired in imitation of various other instruments, whereas the ordinary musical instrument, such as the violin, produces sound tones of fixed and known characteristics. The instrument is not limited. however. to the production of music but may be employed to generate sounds or operate signals for various purposes.

Other objects and advantages of the invention, particularly with reference to electrical elements and circuits and their arrangements in systems for securing various results in different constructional embodiments which have been devised, will appear from the following description considered in connection with the accompanying drawings in which are shown several modified forms of the invention. Various practical embodiments of the invention are hereinafter described in order to make a full and complete disclosure, but the invention obviously is not limited to the specific arrangements shown and it is to be understood that no limitations thereon are intended beyond those set forth in the appended claims.

Referring to the drawings,

Fig. 1 is a diagrammatic view of electrical circuits and apparatus arranged in accordance with the invention for the production of a single tone of variable pitch;
Fig. 1 is a similar view of a modification;
Fig. 2 is a similar view of a further modification embodying amplifiers;
Fig. 3 is a diagrammatic view of a modified form of reproducer circuit;
Fig. 4 and 5 are diagrammatic views of different forms of control circuits;
Fig. 6 is a diagrammatic view of a system for producing two tones;
Figs. 7 and 8 are similar views of systems for producing four tones;
Fig's. 9 to 14 illustrate means for regulating the volume of the sounds;
Fig's. 15 to 18 illustrate systems for switching the tone on and off by means of a wire connection;
Fig. 19 shows n system for effecting, the same result by a modified form of control;
Figs. 20 to 22 show systems for eliminating the natural oscillations;
Figs. 23 to 26 illustrate systems for regulating the timbre of the sound or tone; and
Fig. 27 illustrates a complete system for simultaneously producing a plurality of sound or musical tones on the same or different pitches, and embodying means for controlling the characteristics thereof.

A preferred form of instrument embodying the invention and operable according to the method embodying the same, comprises the following elements:

I. A control element or electrode with relation to which an object such as the hand or fingers of an operator are moved to control the pitch and character of the sound tones emitted by the instrument. Said element does not function like the antenna in a wireless receiver set or apparatus, i. e., it does not receive or detect radiant energy transmitted from a distant transmitting station, but has novel and radically different function as will appear from the detailed description in connection with the various circuit arrangements illustrated in the drawings.

II. Oscillating circuits adapted to produce one or more beat-notes of audible frequency.

III. Means for regulating the volume of the sound tones.

IV. Means for switching individual sound tones on and off as desired.

V. Means for controlling the timbre of the sound tones.

VI. Means for eliminating or nullifying the natural oscillations of tile amplifier or reproducer to prevent the production of undesirable noises or distortion of the sound tones.

In broad aspect, the means of the invention comprises an oscillating system capable of producing audible sound tones and adapted to be influenced or affected by an object or objects, such as the hands or fingers of an operator moved in proximitive relation to an element thereof, together with a sound re- producer operatively connected to said system. Stated differently. the invention embodies a method and means for producing sound or musical tones characterized by an oscillating system in which the period is varied and the characteristical sound emission from which is changed by the movement of an object or objects in proximitive relation to an element thereof. The said system may be electrical and so arranged that movement of an operators s hands or fingers will change the electric characteristic thereof such as the electrostatic capacity between certain elements which determine the period of the oscillator, but while such a system is disclosed and hereinafter described in detail it is obvious that other types of oscillating systems and other means of control may be employed to accomplish the same result.

In Fig. 1 of the accompanying drawings a system is shown embodying an electrode or control element 1 operatively connected to an electrical oscillating system and an electrical sound reproducer. The electrode or control element is in this instance connected to an oscillator 2 of the electro-ionic. type and to a resonant circuit which is traversed by an oscillatory current the frequency of which depends upon on the constants of the circuit and of the circuits conductivity or inductively related thereto. The oscillator 2 is represented as of the filamentary-cathode type operated by an electron discharge from the cathode but other forms of oscillators be used and are intended to be included by the phrase ‘electro-ionic’.

A second oscillator 4 is shown connected to the circuit, 3, said last mentioned oscillator with the oscillator 2 being arranged to control a third electro-ionic tube through coils 6 and 7 which are inductively related to the two oscillators. A condenser 8 is represented as interposed between the coils 6 and 7 and the tube 5, and a grid-leak resistance 9 is shown connected between the grid terminal of said condenser and the cathode circuit. The output circuit of the tube 5 is connected through the audio transformer 10 to a tone reproducer or loudspeaker 11. The tubes 2,4 and 5 are connected to a suitable source of current. such as a battery, as indicated at 12.

The oscillating frequencies of the oscillators 2 and 4 are preferably above the range of audibility, but are nearly the same so that the interference frequency produced in the circuit of the tube 5 will be relatively low and produce a beat-note of audible pitch in the loud-speaker 11. The frequencies of vibrations in the circuit of the tube 5 may he called audible frequencies as they will have substantially the same number of vibrations as the vibrations of an audible sound wave. The pitch of this note. and the presence and strength of the overtones are controlled by selection and arrangement of the condensers, inductances and other elements of the circuits in a known manner.

The frequencies of the oscillators 2 and 4 may be of the order of 500,000 cycles per second, the precise frequency being so chosen that no interference with radio broadcast reception is produced. The values of inductance and capacitv employed in the oscillating circuit are selected in accordance with well known principles to provide the desired frequencies and the variation of the capacity of the variable oscillator is effected by the change of capacity of the control electrode, which change in capacity in instruments that have been built is of the order 10-8 micro-farads. It will be understood that this change of capacity effected by external control is so correlated with the capacity in the oscillator circuit that the resultant range of pitch of the musical instrument covers several octaves.

The sound generated in and emitted through the loudspeaker is also controlled by the movement of an object or objects such as an operators fingers in proximitive relation to the electrode or control element 1 which is connected to the oscillating circuit 3 and to thc grid of the oscillator 2. The electrical characteristics of said control element influence the period or frequency of the oscillator 2 and the character of the beat note in the reproducer. As the operators fingers are moved in suitable relationship with said control element the pitch of the beat note in the reproducer 11 is varied, and continuous variations may be produced with most delicate graduations by the continuous movement of thc fingers.

This control is primarily the result of changes occurring in the electrostatic capacity between the control element and the ground potential or between the control element and other elements of the circuits. Therefore. it is obvious that other objects than the operators fingers would be operable to vary the tone produced. Furthermore, it will be appreciated that the amount and direction of the controlling element will depend somewhat upon the dimensions and arrangement of the control element which may be of such character that movement of the fingers to the extent required to play any ordinary instrument such as the violin will produce a corresponding effect and note change in the present sound generating instrument so that one who has learned to play the violin or some other instrument will have little difficulty in playing the present instrument.

The system shown in Fig. 1a is similar to that shown in Fig. 1, except that coupling condensers 13, and 14 are substituted for the inductive coupling between the circuits of the latter. A great many other modifications of this kind may be made in the arrangement of the electrical oscillating system without departing from the scope of the invention.

In Fig. 2, a further modification including amplifiers is shown. Amplification of the electrical currents may he effected in various ways. but it is preferable to use an arrangement in which there is a minimum distortion of the sound tones. It is also generally preferable to amplify each of the high frequency currents separately. rather than the low frequency beat-note, although a low frequency amplifier may also be utilised.

Referring to Fig. 2, an electrode or control element 15, is shown connected to an oscillator 16, the output of which is connected to an amplifier 17, preferably of the electro-ionic type as represented. A second or auxiliary oscillator is shown connected to to a second amplifier 19. The output circuits of said amplifiers 17 and 19 are connected to the input electrode or grid of an electro-ionic tube 20, whereby a beat note of audible frequency is produced in the output circuit thereof. The output circuit of the tube 20 is connected through a transformer 21, and through an audio-frequency amplifier 22, to a loudspeaker 23. An anode battery 25, is connected in parallel to all of the electro-ionic tubes in the usual manner. A non-inductive resistance 24, is connected between the grid and the cathode of the tube 20 and a condenser 26, is connected between the grid of tube 20 and the anode of the amplifier tube 19. A second condenser 27, is connected between the condenser 26, and the battery 25. This condenser is preferably variable as indicatcd. Condensers 28 and 29 corresponding with the condensers 26 and 27 are also provided in connection with the amplifier 11.

In the arrangement just described, the high frequency oscillations of the controllable oscillator 16, and the auxiliary oscillator 18, are amplified separately and then the combined oscillations are amplified together. In Fig. 1 of the accompanying drawings a system is shown embodying an electrode or control element 1 operatively connected to an electrical oscillating system and an electrical sound reproducer. The electrode or control element is in this instance connected to an oscillator 2 of the electro-ionic. type and to a resonant circuit which is traversed by an oscillatory current the frequency of which depends upon on the constants of the circuit and of the circuits conductivity or inductively related thereto. The oscillator 2 is represented as of the filamentary-cathode type operated by an electron discharge from the cathode but other forms of oscillators be used and are intended to be included by the phrase ‘electro-ionic’.

A second oscillator 4 is shown connected to the circuit, 3, said last mentioned oscillator with the oscillator 2 being arranged to control a third electro-ionic tube through coils 6 and 7 which are inductively related to the two oscillators. A condenser 8 is represented as interposed between the coils 6 and 7 and the tube 5, and a grid-leak resistance 9 is shown connected between the grid terminal of said condenser and the cathode circuit. The output circuit of the tube 5 is connected through the audio transformer 10 to a tone reproducer or loudspeaker 11. The tubes 2,4 and 5 are connected to a suitable source of current. such as a battery, as indicated at 12.

The oscillating frequencies of the oscillators 2 and 4 are preferably above the range of audibility, but are nearly the same so that the interference frequency produced in the circuit of the tube 5 will be relatively low and produce a beat-note of audible pitch in the loud-speaker 11. The frequencies of vibrations in the circuit of the tube 5 may he called audible frequencies as they will have substantially the same number of vibrations as the vibrations of an audible sound wave. The pitch of this note. and the presence and strength of the overtones are controlled by selection and arrangement of the condensers, inductances and other elements of the circuits in a known manner.

The frequencies of the oscillators 2 and 4 may be of the order of 500,000 cycles per second, the precise frequency being so chosen that no interference with radio broadcast reception is produced. The values of inductance and capacitv employed in the oscillating circuit are selected in accordance with well known principles to provide the desired frequencies and the variation of the capacity of the variable oscillator is effected by the change of capacity of the control electrode, which change in capacity in instruments that have been built is of the order 10-8 micro-farads. It will be understood that this change of capacity effected by external control is so correlated with the capacity in the oscillator circuit that the resultant range of pitch of the musical instrument covers several octaves.

The sound generated in and emitted through the loudspeaker is also controlled by the movement of an object or objects such as an operators fingers in proximitive relation to the electrode or control element 1 which is connected to the oscillating circuit 3 and to thc grid of the oscillator 2. The electrical characteristics of said control element influence the period or frequency of the oscillator 2 and the character of the beat note in the reproducer. As the operators fingers are moved in suitable relationship with said control element the pitch of the beat note in the reproducer 11 is varied, and continuous variations may be produced with most delicate graduations by the continuous movement of thc fingers.

This control is primarily the result of changes occurring in the electrostatic capacity between the control element and the ground potential or between the control element and other elements of the circuits. Therefore. it is obvious that other objects than the operators fingers would be operable to vary the tone produced. Furthermore, it will be appreciated that the amount and direction of the controlling element will depend somewhat upon the dimensions and arrangement of the control element which may be of such character that movement of the fingers to the extent required to play any ordinary instrument such as the violin will produce a corresponding effect and note change in the present sound generating instrument so that one who has learned to play the violin or some other instrument will have little difficulty in playing the present instrument.

The system shown in Fig. 1a is similar to that shown in Fig. 1, except that coupling condensers 13, and 14 are substituted for the inductive coupling between the circuits of the latter. A great many other modifications of this kind may be made in the arrangement of the electrical oscillating system without departing from the scope of the invention.

In Fig. 2, a further modification including amplifiers is shown. Amplification of the electrical currents may he effected in various ways. but it is preferable to use an arrangement in which there is a minimum distortion of the sound tones. It is also generally preferable to amplify each of the high frequency currents separately. rather than the low frequency beat-note, although a low frequency amplifier may also be utilised.

Referring to Fig. 2, an electrode or control element 15, is shown connected to an oscillator 16, the output of which is connected to an amplifier 17, preferably of the electro-ionic type as represented. A second or auxiliary oscillator is shown connected to to a second amplifier 19. The output circuits of said amplifiers 17 and 19 are connected to the input electrode or grid of an electro-ionic tube 20, whereby a beat note of audible frequency is produced in the output circuit thereof. The output circuit of the tube 20 is connected through a transformer 21, and through an audio-frequency amplifier 22, to a loudspeaker 23. An anode battery 25, is connected in parallel to all of the electro-ionic tubes in the usual manner. A non-inductive resistance 24, is connected between the grid and the cathode of the tube 20 and a condenser 26, is connected between the grid of tube 20 and the anode of the amplifier tube 19. A second condenser 27, is connected between the condenser 26, and the battery 25. This condenser is preferably variable as indicatcd. Condensers 28 and 29 corresponding with the condensers 26 and 27 are also provided in connection with the amplifier 11.

In the arrangement just described, the high frequency oscillations of the controllable oscillator 16, and the auxiliary oscillator 18, are amplified separately and then the combined oscillations are amplified together.

In Fig. 3, a further modification of the amplifier is shown. The left hand portion of Fig. 3 is the same as Fig. 2 as far as the line III-III. The amplifier 22 is shown connected with the transformer 21 to which are connected four amplifiers 31, 32, 33 and 34, the latter being inductively connected with the amplifier 22 through the transformer 30. In this instance amplifiers 32, 33 and 34 are connected in parallel to obtain direct current intensification, and said three amplifiers are connected in group to the fourth amplifier 31. The tone reproducer 23 and the anode battery 25 are connected as in Fig. 2. This arrangement is suitable especially by reason of its high efficiency for comparatively low frequencies, particularly for bass tones.

The oscillations. of the controllable oscillator and the fixed oscillator are made independent of each other and for such reason the amplification of each current takes place separately. Each oscillation is thus first amplified individually and then only is amplification of the combined oscillations effected.

Schematics

Technical