Patent GB-308988-A (GB)
Title: Improvements in electrical musical instruments
IPC: G01V3/14
Filed: 1929-04-02
Abstract: 308,988. Martenot, M. L. E. April 2, 1928, [Convention date]. Electrically-vibrated instruments. - In electrical musical instruments utilizing oscillating currents, the frequency is varied by adjusting variable inductances capacities or resistances provided with movable flexible conductors, the flexible conductors facilitating adjustment of, and forming parts of, the controlling devices. In Fig. 1 the variable inductance comprises a flexible wire or band 1, of preferably decreasing cross-section, attached by a wire 7 to a spring drum 5 and moved relatively to a coil 1<a> by the operator through an insulating finger-piece. 2. An indicator 4 attached to the wire 7 moves over a scale 6 to show the note produced. In Fig. 2 (not shown the variable inductance comprises a wire which may be more or less unwound from the grooves of an insulating spring drum, with or without a fixed coil near or on the drum to form a variometer. Fig. 3 shows a variable condenser comprising a metal cylinder 10 with dielectric 11 of varying thickness on which is wound a wire 12 attached to a finger-piece 13. In Fig. 4 (not shown) the turns of wire are within a metal cylinder. These condensers may be connected by reduction gearing to an ordinary condenser, or to a variable self-inductance, or to a variometer, by which fine adjustments can be obtained. In Fig. 5, a variable condenser comprises a band 16 connected to a finger-piece 20 and by a cord 17 to a spring drum 18a, and another metallic body 19, of wedge shape. The band 16 is formed of fine wire wound on insulating material. Alternatively the ends 16<a>, 17<a> of the band and cord may be joined, (Fig. 6, not shown), and, in lieu of an indicator 22 and scale 23, a finger-ring working over a dummy keyboard may be provided. Or the graduations may be on the cord 17 working past a fixed pointer. A variable resistance comprises an insulating drum coated with a film of graphite on which is wound more or less a metallic wire or band. Fig. 7 shows a finger-piece 36 which is connected to one of the flexible conductors 16 and is provided with small plates 34 of varying sizes and with fixed metallic keys 35. By placing a finger on a key the capacity of that finger is added, giving additional control over the pitch of the sounds. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the following:- A keyboard (or octave thereof) mounted on springs may be vibrated by the operator's hand to vary the frequency or intensity by varying a capacity inductance or resistance, so as to produce a vibrato effect; this forms the subjectmatter of Specification 335,997. Or a vibrato of constant frequency may be produced by a condenser having one plate connected by a spring to the keyboard which is given an initial shake. To vary frequency by varying inductance, a copper plate or a magnet may be moved by hand near an inductance; or by varying resistance, a wire may be variably immersed in a poorly conductive liquid. Scales or dummy keyboards may be applied to instruments in which the hand is moved near an aerial, a pointer moving over the scale reproducing the movements of the hand. A keyboard with fixed metallic keys may be connected through different inductances or resistances. Fixed insulating keys of different thicknesses, or a single key of varying thickness, may rest on a metal wire or plate to vary the frequency according to the point touched. A keyboard for any electric instrument has keys connected to resistances to give different sound intensities according to the extent of depression of a key. Instruments with keyboards and with an aerial co-operating with the hand may be combined. A selenium cell connected in the oscillating circuit either directly or by a relay, may control intensity or frequency. The apparatus may be automatically operated. This subject-matter does not appear in the Specification as accepted.