On the design of diaphragms capable of continuous tuning

• Published in: Proceedings of the Royal Society of London. Series A, Containing papers of a mathematical and physical character Containing papers of a mathematical and physical character, 1921-05, Vol.99 (697), p.163-171
• Main Author: King, Louis Vessot
• Format: Article
• Language: English
• Subjects: Acoustic resonance; Air masses; Audio frequencies; Damping; Frequency ranges; Hysteresis; Microphones; Sound pitch; Sound waves; Vibration
• ISSN: 0950-1207; 2053-9150
• DOI: 10.1098/rspa.1921.0031

In calculating the acoustic characteristics of an electrically operated submarine sound-generator fitted with a spring-controlled diaphragm, it was found that the apparatus would not radiate efficiently at a given power input and frequency, unless the effective diameter was, within fairly narrow limits, of the correct size, and unless the fundamental pitch was very close to the frequency of the alternating current supplied. The calculations also showed that a non-periodic diaphragm (i. e., one in which there is no elastic restoring force) could not be set into vibration at frequencies in the neighbourhood of 500 cycles without incurring very high copper losses. A similar conclusion was reached with regard to the aperiodic diaphragm. It was concluded that the best efficiency could be secured by operating the sound-generator with alternating current of the same frequency as that of the diaphragm. Similarly, in most forms of sound-receiving apparatus, the response to submarine sound-waves is most marked when the size of the diaphragm is correctly chosen and when its fundamental pitch is in resonance with the frequency of the incident waves. In the field of submarine acoustic signalling it is evident that a great advantage is to be derived by utilising a means of continuously tuning the diaphragms of the sound-receivers or generators over a certain range of frequencies, thus realising selective transmission and reception. At the same time advantage is taken of the great increase in sensitivity characteristic of highly selective receivers, in which the damping may be reduced to a minimum in view of the possibility of being able to “tune in” to incoming waves as is now done in radiotelegraphy.