Patent GB-414352-A (GB)
Title: Electrical musical instrument
IPC: G10H3/18
Filed: 1932-10-31
Abstract: 414,352. Electrical musical instruments. JACKSON, L. MELLERSH-, 28, Southampton Buildings, Chancery Lane, London.-(Vierling, O.; 7, Kloedenstrasse, Berlin.) Oct. 31, 1932, No. 30574. [Class 88 (ii).] In an electrical musical instrument wherein the vibrations of key-operated tuned mechanical vibrators (e.g. strings, forks or bars) are electrostatically or electromagnetically translated into sound, to improve the tone quality at least some of the vibrators are coupled together by a vibratile system which radiates no appreciable sound. In Fig. 2, the vibratile system consists of the bridge 3 and its mounting of wooden bars 11, the bars being preferably arched and in slight longitudinal compression. Bass strings may be strung over a separate bridge mounted on the same bars. Acoustic shielding 19 of felt &c. may be provided. An electrostatic strip 7, insulatedly mounted on the frame 5, forms a capacity with the strings and transmits electric oscillations corresponding to their vibrations to a thermionic tube, amplifiers, volume control and loud-speaker. The strip 7 may instead be mounted either on the bridge 3 or on the bars 11 (Figs. 21, 22, not shown). The bars 11 may be omitted, the bridge 3 being arched and secured by extensions thereof screwed to the frame ; and an electromagnetic or mechanical lock may be provided to render the bridge immobile, particularly in a vertical direction, if it is desired, as for organ tone, to decrease the damping produced by the coupling (Figs. 4 to 9, not shown). In Fig. 10, two strings 111, 112, tuned in unison, for each note, pass over a bridge 108<1> mounted on bars as in Fig. 2. Hammers 117, shiftable by a handle 150 strike either or both sets of strings. The vibrations of either or both sets of strings are translated. In the position shown, strings 111 are struck but, though connected to positive of battery 134, their vibrations are not translated owing to the absence of an effective capacity-strip. The gradually increasing sympathetic vibrations of strings 112 are however translated by a capacity-strip 122 having pins 121 projecting close to the strings 112. By connecting strings 111 by switch 141 instead to battery negative, non-translation from strings 111 is further ensured, in which case pins 121 may be omitted and a simple strip 122 used. If a strip 124 is by switch 131 substituted for strip 122, and both sets of strings are connected to battery positive, the vibrations of both the struck strings 111 and the coupled strings 112 will be translated. This results in an emphasis of the beginning of a tone, since the gradually increasing vibrations of the coupled string are out of phase with respect to the struck string. The neutralizing effect may be eliminated by connecting strings 112 by switch 142 to battery negative, the percussion tone of strings 111 being then produced modified however by a reduction in the rate of damping by the bridge which is stabilized by the phase opposition of the coupled string. The strip 124, and the strip 122 with pins 121 may also be used together. In Fig. 13 (not shown) two strings, in unison but preferably differing in length, are used for each note, the longer strings passing clear of the bridge and being therefore uncoupled. Two capacity strips cross the strings at different points along their lengths and are connected each through its own thermionic valve, transformer and potentiometer, finally to the loud-speaker. By striking the shorter strings only, pianoforte tone is obtained, modified according to the proportional mixing (one component in opposite phase if desired) performed by the potentiometers, of the oscillations received from the two strips. Organ and other (including percussion) tones are obtained when the hammers are shifted to strike the longer strings only, means as described in Specification 412,279, including contacts on the hammer and check, being provided whereby the efficiency of translation is varied after the striking of a note, so that the impact components are eliminated, or the percussion tone is produced with or without either additional decrease in amplitude, or a tendency to increase in amplitude, after inception. The hammers may be arranged always to strike both strings, the set of strings from which translation is to be made being selected by electric switches. Or further tones may be produced by translating from both sets together. In Fig. 15, means are shown whereby a flat soundboard 310 with ribs 311 may be optionally linked to the non- radiating vibratile system comprising the bridge 305 mounted on the ribs 304. Electromagnets 316 secured to the underside of the bridge 305 are normally out of contact with armatures 313 mounted on rods 312 secured to the soundboard, but are looked thereto on closing switch 318. Electrostatic shielding consisting of a coating of colloidal graphite on members 301, 302 and under the lid 337, and of a wire screen 340, is provided. For use instead of the loudspeaker 333, or as an alternative to the electromagnetic coupling of the soundboard 310 to the bridge 305, the soundboard 310 may be vibrated by voice-coils which are mounted thereon and are energized from leads 351, cooperating with polepieces which are mounted on the beams 303 and are energized by field coils ; a sound-insulating sheet and stuffing round the beams prevent acoustic back-coupling of the strings (Fig. 17, not shown). The distance of two strings, which may relate to the same note, from the translating-strip 324, may be simultaneously adjusted by engagement on opposite sides of a screw 353, Fig. 18, in a groove therein, the strings being then crossed and passed on opposite sides of a pin 354. Organ-like tones are also obtained at will by a construction illustrated in Fig. 19 (not shown) employing for each note two approximately similar struck strings of which the corresponding electric oscillations are on operation of a switch combined in opposite phase, the vibration of one set of strings being mechanically damped. The frame, wrest-plank, strings, and the bridges with their supporting bars, may form a unitary structure removable from the instrument (Fig. 24, not shown). A tremolo arrangement comprises variable resistances, each consisting of a pile of graphite discs, placed under the keys and included in the circuits loading the strings ; variable pressure on a key produces a variable efficiency of the electric translation (Fig. 26, not shown). The quality of the tone may also be partly controlled by controlling the force exciting the vibrators, e.g. by an adjustable hammer rest-rail. Specification 408,998, also is referred to.