The Use of Rochelle Salt Crystals for Electrical Reproducers and Microphones

The paper begins with a brief historical résumé of the development of piezo activity for acoustic uses. References are given. Methods developed by the author and his associates permit the cheap commercial production of Rochelle salt crystals and sections thereof, but the saturation and variation with temperature of Rochelle salt (shown in diagrams) must be compensated for by special assemblies of the Rochelle salt sections. The underlying principle of the special assemblies is that of mutual opposition with resultant magnification of motion. This principle of opposition may be utilized to produce bending or twisting elements of Rochelle salt of great simplicity. Such elements may then be combined with appropriate acoustic members to operate with great sensitivity and efficiency in either an input or output circuit. Rochelle salt requires no exciting field of any sort, which property results in the elimination of the necessity for any external excitation. Microphones, pick-ups, and especially speakers are described, with some discussion of limiting conditions of load, temperature, and other operating conditions. The article concludes with a tabulated summary of advantages offered by the use of Rochelle salt sections.