Bibliography

I. G. Dreizen, Course in Electroacoustics, Part I, Moscow, State Publishing House for Communications and Radio, 1938, 387 pp., price 9 rubles.

The title of the book does not quite correspond to its contents. I. G. Dreizen’s course is, strictly speaking, more a textbook for a technical college on technical acoustics than on electroacoustics in the narrow sense of the word. In particular, the first part under review contains basic information on the theory of sound, physiological acoustics, and architectural acoustics.

At present there is no serious course in technical acoustics in Russian in which the questions of the theory of sound and its many technical applications are treated with sufficient depth and system. I. G. Dreizen is making an attempt to fill such a textbook gap, and his initiative should be welcomed in every way. The author’s task was undoubtedly difficult, and he has not succeeded in carrying it out fully. It must be admitted that the course does not yet have a homogeneous character in the sense of conceptual unity, style, and system of exposition. It still retains too many features of the individual sources used by the author and has not been brought into a single coherent system. For the student of the subject, this gives rise to a number of difficulties and ambiguities, which lowers the pedagogical value of the book.

At the same time, the course possesses a number of unquestionable merits. It is very valuable that a unified system of terminology and notation has been carried through in it; this facilitates the study of the subject. Formulae and figures are marked by a double number—the number of the chapter and the serial number within that chapter. This system is convenient and should be promoted. The bibliography is given quite fully. The tabular material at the end of the book, however, is rather meager—only mathematical tables.

Chapter I sets forth questions concerning the composition, dynamics, and perception of sound. One might have wished for somewhat fuller data on sound material important for practice and subject to transmission by electrical circuits.

Chapters II and III examine the basic questions of the theory of the sound field, sound radiators and receivers, the theory of sound propagation in tubes and horns, and the theory of four-terminal networks and filters.

Chapters IV, V, and VI contain an exposition of room acoustics, the theory of reverberation, and questions of sound absorption and sound insulation.

Chapter VII is devoted to the design of broadcasting studios. In this chapter, the presence of information on lighting engineering and ventilation is somewhat puzzling. Although this information is, of course, needed by an engineer designing a studio, it nevertheless does not relate to acoustics, and should have been given, at most, in the form of appendices rather than in the main text.

The exposition of all questions of theory is, as a rule, conducted carefully and systematically, for the most part with mathematical derivations, and provides sufficient material for technical calculations in the simplest cases. The appendix gives the theory of spherical and cylindrical waves, including the theory of diffraction (after Morse). The material presented will undoubtedly be useful to acoustic engineers. A number of questions are presented by the author very successfully. This applies, for example, to the theory of four-

loudspeakers as applied to acoustics, to the theory of horns, to the theory of reverberation, and to the calculation of studios. A number of new figures and many useful graphs and nomograms are given.

A number of particular shortcomings should be noted. In Ch. IV, chiefly obsolete methods of measuring reverberation are set forth in detail. The most important new methods, based on the use of fast-acting meters of sound-intensity level, are for some incomprehensible reason not considered.

In setting forth the question of reverberation in electroacoustically linked rooms, no account is taken of the fact that the reverberation of the primary and secondary rooms is not equivalent, since the primary reverberation is perceived through the reproducer and seems to be connected with it. Thus these two reverberations cannot be added.

On p. 206, in deriving the equations for the propagation of sound in an absorbing material, the author proceeds from an analogy with an electrical line. It would have been far more convincing to derive the corresponding equations for the acoustical case. The physical picture would thereby have become much clearer. In the presentation of Cremer’s theory for absorbing materials (§ 4, Ch. V), the basic idea remains unclear, from which one can find the required thickness of a material and its resistance if it is necessary to obtain an absorption coefficient greater than some prescribed value in the region of frequencies above some limit. Conversely, from the exposition on p. 210 (Table 5, III) one may get the erroneous impression that special materials (Celotex, etc.) can give the same absorption as cotton wool, but with a much smaller thickness.

On p. 220, in discussing the difference in the values of the absorption coefficient measured by the tube method and by the reverberation method, nothing is said about the possibility of strong sound absorption during sliding along the surface, which could explain the observed contradictions. Nor is the factual material available on this important question presented, and the fundamental importance of measurements by the tube method is not emphasized.

In Ch. VI, § 4, in the exposition of the question of the sound insulation of homogeneous walls, neither their graphs summarizing numerous measurements nor empirical formulas are given, which would have provided the reader with valuable support for practical calculations.

In presenting the results of Wintergerst’s experiments (p. 249), concerning the passage of sound through openings, it is not indicated that these results were obtained in a tube and that they are not applicable to free sound waves.

In conclusion let us note several oversights made by the author. In Figs. 4 and 7 (p. 162), the ordinates in the drawing refer to the case of measuring distances in feet (according to American data), which should have been indicated. On p. 284 it is stated that, with nonparallel walls, the danger of the formation of standing waves in a room disappears—this, of course, is incorrect: standing waves will form; only the nodal surfaces will have a more complicated shape. On p. 220, designs of multilayer doors are presented, the usefulness of which, from my point of view, is very doubtful; these designs are inspired by the idea of the passage of longitudinal waves from one medium into another, but they do not take into account the possibility of membrane vibrations and the role of the joints in a complex construction. Solid heavy doors will probably be simpler and better than layered ones.

The shortcomings noted are not of fundamental significance for the evaluation of the book as a whole and can be corrected in the next edition. I consider that the course by I. G. Dreizen is a valuable contribution to our literature on technical acoustics.

S. N. Rzhevkin, Moscow