1. The New Encyclopaedia Britannica, Macropaedia, Vol. 17. Encyclopaedia Britannica, William Benton, Helen Hemmingway Benton (Publishers), 15th edn, 1974, pp 19–51
2. The New Encyclopaedia Britannica, Macropaedia, Vol. 17. Encyclopaedia Britannica, William Benton, Helen Hemmingway Benton (Publishers), 15th edn, 1974, p 843
3. Linear acoustic theory;Morse,1961
4. Active Control of Sound;Nelson,1992
5. Mathematical Methods for Physicists;Arfken,1970