Journal of the Society of Motion Picture and Television Engineers (1950-1954)

Book Reviews Acoustic Measurements, by Leo L. Beranek Published (1949) by John Wiley & Sons, 440 Fourth Ave., New York 16. 896 pp. + 17 pp. index + VII pp. " 519 illus. 6 X 8'A in. Price, $7.00. This much needed book is a comprehensive collection of techniques and of tables of constants which the acoustic engineer requires for measurements and calculations. Of interest is a brief history of acoustic measuring instruments; and of reference value is a glossary of terminology. Dr. Beranek presents the solutions of the sound wave equations in various forms, with complete data on the velocity and attenuation in a great variety of media including effects of wind, jungle growth, etc.; and he also gives the experimental and calculated diffraction effects due to variously shaped bodies placed in the path of a plane. Then follows an excellent treatise on techniques of calibrating microphones as standards for measuring sound pressures with particular emphasis on the reciprocity method. The methods generally used for measuring frequency are clearly presented with some good photographs of commercial instruments available The chapter on the principles of calibrating pure tone audiometers is timely because of current efforts to develop specifications for a standard audiometer. The author discusses various types of meters for measuring quantities related to sound intensity such as peak meters, V. U. meters, level recorders, RMS meters, and also meters for analyzing transient and steady sounds into various sorts of components. The basic tests for the efficiency of communication systems to transmit speech are itemized and described, such as methods of measuring frequency and nonlinear response characteristics, repetition counts, syllable, word, and sentence articulation tests, and threshold measurements of received speech. Methods are given in detail for testing the three basic elements of a communication system: the microphone, the line (including amplifier), and the headphone or loudspeaker. In each case the author has outlined the method of testing the frequency response, the power efficiency, the impedance, the nonlinear distortion, and overload capacity. With the discussion on loudspeakers there is a useful set of curves for determining power rating to give satisfactory loudness of speech or music in rooms of any size and treatment. There is one chapter on real voice testing methods of determining response characteristics of microphones and earphones. It is shown how these principles can be applied in a convenient form for testing the important characteristics of hearing aids. Methods of making articulation tests are outlined together with lists of syllables, of words, and of sentences, including the P. B. and Spondee tests. The last three chapters are devoted to measurements of the acoustic properties of rooms, including the various methods of measuring the absorption properties of materials for treatment of such rooms. References throughout the book are numerous and should permit a student to pursue very satisfactorily any special phase. Many engineers will be grateful to Dr. Beranek for bringing together in such a convenient form so much technical information bearing on acoustic measurements. HARVEY FLETCHER (Columbia University) 5 Westminster Rd. Summit, N.J. 117