240 MISCELLANEOUS TRANSDUCERS 



10.4. Electrical Musical Instruments i^. — The vacuum tube oscillator 

 and amplifier has opened an entirely new field for the production of sound 

 of practically any frequency, quality or amplitude. Many musical instru- 

 ments employing various types of vibrating systems and associated vacuum 

 tube oscillators and amplifiers have been developed. 



The simplest system for the amplification of string instruments like 

 violins, guitars, banjos, pianos, etc., consists of a vibration pickup attached 

 to the body or sounding board, an amplifier and a loud speaker. 



Electric pianos'^ have been developed in which the vibrations of the 

 strings are converted into the corresponding electrical variations. In one 

 system, the variation in capacity between the string and an insulated plate 

 is used in a manner similar to the condenser microphone. In another, the 

 string acts as an armature in an electromagnetic system. The outputs of 

 the pickup systems are amplified and reproduced by means of loud speakers. 



One type of electric organ^^ consists of a number of small alternators 

 (one for each note), a keying and mixing system for adjusting the quality, 

 an amplifier and a loud speaker. Another electric organ^'^ employs wind 

 driven reeds. The vibrations of the reeds are converted into the corre- 

 sponding electrical variations, amplified and reconverted into sound by 

 means of loud speakers. 



A versatile electronic musical instrument i^-^s^ in which the wave shape 

 and harmonic content may be varied over wide limits derives the needed 

 frequencies from twelve high frequency oscillators followed by cascade 

 frequency dividers in which the frequency is divided in each stage. The 

 overtone structure of each note is made a function of the input level by the 

 use of an over-biased nonlinear amplifier. Practically any musical instru- 

 ment such as the organ, piano, guitar, violin, trombone, etc., can be simu- 

 lated by this instrument. 



Electric carillons^^ consisting of tuned coiled vibrators, magnetoelectric 

 translators, amplifiers and reproducers possess qualities which are quite 

 similar to the conventional carillons. 



The voder^° is an electrical arrangement which corresponds to the mech- 



^^ For a comprehensive paper on " Electronic Music and Instruments," Miessner, 

 B. F., Proc. I. R. E., Vol. 24, No. 11, p. 1427, 1936. 



" Miessner, B. F., Proc. I. R. E., Vol. 24, No. 11, p. 1427, 1936. 



i« Hammond, L., U. S. Patent 1,956,350. 



" Hoschke, U. S. Patent 2,015,014. 



18 Hammond, L., Science, Vol. 89, p. 6, Feb. 10, 1939. 



18^ Hammond, L., Electronics, Vol. 12, No. 11, p. 16, 1939. 



" Curtiss, A. N., U. S. Patent 2,026,342. 



^ Bell Laboratories Record, Vol. 17, No. 6, Feb., 1939. 



