Patent GB-421662-A (GB)
Title: Improvements in electrical musical instruments
IPC: G10H3/06
Filed: 1933-08-01
Abstract: 421,662. Electrical musical instruments. HOBSON, P. T., Briggate, Bower Mount Road, Maidstone. Aug. 1, 1933, Nos. 21549/33 and 240/34. [Class 88 (ii)] In an instrument wherein stationary light sources coact with a toothed or apertured moving member such as a band, disc or cylinder, the light oscillations being converted into electric oscillations by photo-electric means and then led, amplified if necessary, to a loud-speaker, one light source is used for a note to be sounded as a fundamental, and another if the note is to be sounded as a harmonic of some other fundamental. In Fig. 5, discs D<1> .... are each perforated with twelve circular rows of holes, representing the notes of one octave, the discs being geared successively at 2: 1 to give successive octaves. The last discs are utilized for harmonics only. The holes are of the same diameter and of the same radial spacing between rows ; centres of adjacent holes in a row are as near as possible two diameters apart. Radial " shutter boxes " F<1>, F<2> .... in front of the discs sound fundamental notes, 1H<1>, 1H<2> ... the first harmonics, 2H<1>, 2H<2> ... the second harmonics, and so on. The shutter boxes, Fig. 3, each comprise a strip lamp at 14 and twelve shutters 17 which control apertures 15 and are operated from the keys by means of electromagnets 23, allowing light fluctuating substantially sinusoidally to fall, through lenses if necessary, on the photoelectric cell or cells behind the discs. The cells may be connected to separate tappings on a battery, to enable them to be brought individually to the required sensitivity. The cells relating to the lower part of the compass may be connected to a separate amplifier and loudspeaker to allow of greater amplification if necessary. Each key K<1>, K<2> .... , Fig. 5, is connected to its appropriate electromagnets in fundamental and harmonic shutter-boxes to enable the fundamental and five (except for some of the top notes) harmonics to be sounded if required. The timbre is controlled by connecting the strip lamps S<1>, S<2> ..., Fig. 6, of all the fundamental shutter-boxes F<1>, F<2> ..., and likewise the lamps of the shutter-boxes of each harmonic, in parallel, and in circuit with sets of predetermined resistances r<1> .... r<6> as shown. A stop-key actuates a selected electromagnet R<1> .... , connecting the boxes through the appropriate set of resistances whereby the lamps for the fundamentals and harmonics are illuminated with the correct relative brilliance for the particular stop. If two or more stops are simultaneously in action, additive effects are produced. Similar additive effects may be arranged when the same note is simultaneously played on another manual with a different stop combination. Tremolo may be obtained by superposing a low frequency modulation on the D.C. lamp-supply M, or by oscillating the shutter-boxes, or by a periodic brake on the discs; swell effects by general volume control. " Formant" frequencies, consisting of notes of certain pitches depending on the stop in use and sounded whatever note is played, may be added by separate light sources co-operating with the foregoing or additional discs.