1. A. E. Kenne11y, Electrical vibration instruments, page 190, New York 1923.
2. R. D. Fay, J. Acous. Soc. Am.15, 32, 1943.
3. J. E. White, J. Acous. Soc. Am.18, 155, 1946.
4. C. W. Kosten and C. Zwikker, Akust. Zs.6, 124, 1941.
5. J. B. Crandall, Theory of vibrating systems and sound, page 188, London 1927.