CONGRESSES AND CONFERENCES

SECOND ALL-UNION ACOUSTIC CONFERENCE

S. N. Rzhevkin

From December 1 to 5, 1935, the Second All-Union Acoustic Conference, convened by the Academy of Sciences jointly with the Association of Physicists of the People’s Commissariat of Heavy Industry, was held in Moscow.

In terms of the number of delegates who gathered, the number of papers, and the scope of the organizational questions it covered, the conference was considerably broader than the first, which had met in 1931 in Leningrad. The convening of the conference was preceded by substantial organizational work, carried out chiefly by the Moscow Acoustic Section of the Association of Physicists. The difficulty of the organization lay in the fact that it was necessary to identify all the numerous institutions engaged in acoustics throughout the Union, scattered among all the chief people’s commissariats of the Soviet Union.

The conference included the following sections: physical, physiological, architectural-musical acoustics, electroacoustics, sound cinema, and noise control. The number of scientific papers presented at plenary sessions was 10; in the sections, more than 100. The number of delegates present was more than 150. The conference gave a complete picture of work in acoustics in the USSR and made it possible for a large number of specialists from diverse fields to enter into direct communication.

At the plenary sessions of the conference a number of interesting scientific papers on general questions of acoustics were heard. Academician P. P. Lazarev set forth the foundations of the ionic theory of hearing developed by him, which is widely known and makes it possible to explain a number of important features of auditory perception, in particular difference sensitivity of hearing to tones of different pitch, adaptation (fatigue) of hearing, and a number of other phenomena.

The Hungarian physicist Dr. Georg von Békésy (Budapest) delivered a paper, “On Phenomena Speaking in Favor of Mechanical Frequency Analysis in the Cochlea.” A series of brilliant experiments carried out by the author makes the hypothesis of mechanical analysis of sound in the cochlea—put forward by Helmholtz and until recently almost certain*—sufficiently credible. Békésy’s experiments on a miniature model of the cochlea are especially convincing; in this model the basilar membrane was implemented in the form of a thin rubber partition. Through the glass walls of this model, when sound acted on it, one could observe the formation of a vortex in the liquid. The localization of the vortex depended on the pitch of the tone: for low tones it was situated closer to the apex of the cochlea, for high tones closer to the base. Studying auditory fatigue at frequencies above and below the acting tone, Békésy succeeded, from the magnitude of the fatigue, in measuring the width

* A translation of Békésy’s article devoted to this question was published in Uspekhi Fizicheskikh Nauk, vol. 15, no. 6, 1935.

excited by the given tone of the strip on the basilar membrane, and this band proved to be much wider than could have been supposed on the basis of studies of the fusion of trills and other experiments of Helmholtz. Békésy advances a theory of excitation of the auditory nerves as a result of the pressure of a localized vortex on the basilar membrane, apperiodic oscillations of the fibers being produced.

From experiments on models it was shown that an impulse propagates along the membrane with a certain velocity and gives a maximum of excitation at some distance from the stirrup. If, in one ear, the sound of an impulse is masked in the far part of the cochlea by a strong low tone, then the maximum of excitation will appear closer to the stirrup and will correspond to an earlier moment in time. Observations show that the sound of the impulse seems, under these conditions, to be displaced toward the ear in which the low tone is imposed, which is explained by the binaural effect (perception of the direction of sound). Thus it may be regarded as proved that the impulse wave travels along the cochlea with a certain finite velocity.

Prof. S. Ya. Lifshits gave a paper “On the Integral Effect of Duration.” Having substantiated experimentally a law according to which the apparent duration of an auditory perception, or its “extent,” is determined by the product of the loudness level of the sound, expressed in decibels, and its actual duration (in seconds), the author extends this law also to visual sensations. The conclusions from these constructions are applied by the author to the substantiation of the theory of optimal reverberation of halls.

Prof. N. N. Andreev, in his report, gave a detailed analysis of the question of the objective characteristics of noise and sound. He especially clearly pointed out that the usual characteristic in the form of the sound spectrum is in principle incorrect for sounds such as noises, in which there is an irregular component. For such sounds one can speak only of a statistical description and of a probable spectrum, similar to the way this is done in the theory of the Schrot effect and fluctuations. A mathematical apparatus corresponding to this problem can be taken in finished form from the works of Shotky, Krutkov, and others. An automatic analyzer gives precisely a picture of the probable spectrum.

Prof. S. Ya. Sokolov gave a survey of his work on the study of ultrasonic oscillations. The author has recently succeeded in obtaining oscillations in quartz with a frequency up to \(2 \cdot 10^8\), which at the present moment is a world record, achieved as the result of great and persistent work in recent years. At ultrahigh frequencies a gradual increase in the velocity of sound in quartz is observed; the increase is approximately \(+20\%\) at the highest frequency. Ultrasonic waves also cause substantial changes in the structure of quartz, revealed on roentgenograms. The structure of solidifying metal under the action of ultrasound changes very strongly—an increase in the number of crystallization centers and a comminution of the crystalline structure are obtained.

The works of S. Ya. Sokolov in the field of constructing underwater ultrasonic radiators, as well as his methods for finding defects in large metal parts by means of ultrasonic sounding, are sufficiently well known, and I shall not dwell on them.

Of the sectional reports we shall dwell, as necessary, only on the most interesting ones and shall stop above all at the works of the section of physical acoustics. On the work on absorption and dispersion of ultrasonic waves in a gas, carried out at the Institute of Physics of Moscow University under the direction of Academician L. I. Mandelstam, the head of the laboratory of vibrations, G. S. Gorelik, reported. An investigation of the velocity of sound at reduced pressures, carried out by E. Ya. Pumper, showed an increase

speed of sound in CO₂. This increase in velocity is entirely analogous to the increase in velocity at high frequencies found and studied in detail by Kneser. In both cases the increase in velocity is due to the slowing down of the exchange of translational energy of molecular motion with their internal energy. When the frequency is increased, this slowing is due to the fact that the period becomes too short for the energy exchange to have time to take place completely; when the pressure is decreased, the slowing is caused by a decrease in the number of collisions of molecules, i.e., by a decrease in the number of cases when exchange can occur. Mathematically it is possible to express these considerations by the fact that the change in the speed of sound depends on the ratio of the frequency \(f\) to the pressure \(p\). E. Ya. Pumper succeeded in reaching the ratio \(f/p = 22.15\) (five times greater than had previously been possible), and a continuous increase in the speed of sound was found.

In the laboratory of oscillations, L. N. Belyavskaya developed, from a proposal by L. I. Mandelstam, a very elegant method for measuring the absorption coefficient of ultrasonic waves by means of a Pierce interferometer. This method makes it possible simultaneously to find the amplitude of oscillations of a quartz vibrator and the piezoelectric modulus of quartz.

Let us note the interesting work on the diffraction of light by a grating of ultrasonic waves in a liquid, carried out at the Physics Institute of Moscow University under the direction of Prof. G. S. Landsberg. A theoretical analysis of the question of diffraction by ultrasonic waves was made by S. M. Rytov, proceeding from Debye’s theory. P. A. Bazhulin investigated the absorption coefficient of sound in a liquid by the method of measuring the intensities of diffraction spectra; he established that the absorption coefficients increase in proportion to the square of the frequency, as follows from Stokes’ law, but the absolute magnitude differs sharply from that calculated according to Stokes’ law. V. K. Khorizomenov developed, at the suggestion of Acad. Mandelstam and Prof. Papaleksi and Landsberg, a method of modulating light by means of a grating of ultrasonic waves. When a high-frequency voltage applied to quartz is modulated, a synchronous change is obtained in the intensity of the light of rays diffracted by the ultrasonic grating. This method of modulation, which is a known advantage over the Kerr cell, was put into practice and demonstrated at a meeting of the section.

The same idea of modulation on an ultrasonic grating was also applied by Prof. S. Ya. Sokolov, who technically developed a method of sound recording for sound cinema.

The work of R. R. Solov’eva and E. P. Ostrovsky in the laboratory of the Roentgen Institute, directed by the author of this article, concerned investigations of the physicochemical actions of ultrasound. It was found that chemical reactions caused by ultrasound (for example, the decomposition of potassium iodide) depend on the amount of dissolved oxygen and hydrogen. It may be thought that in the hydraulic impacts resulting from the collapse of cavitations (voids) formed in the ultrasonic field, an intense release of energy is obtained in a small volume, which apparently leads to the formation of atomic oxygen, which in this case acts as an active chemical agent. The stimulation of plant growth by the action of ultrasound discovered by E. P. Ostrovsky (for example, a threefold increase in the yield of peas and a 40% increase for potatoes were observed) apparently points to a sharp intensification of the action of oxidative enzymes, which is also probably connected with the release of atomic oxygen.

B. G. Shpakovsky (Physical Institute of the Academy of Sciences) proved the absence of dispersion of ultrasound in liquids over a wide frequency range from \(10^5\) to \(7 \cdot 10^6\) Hz. He also found a significant increase in the speed of sound in carbon dioxide near the critical state.

M. S. Antsiferov (Laboratory of the House of Sound Recording) very successfully analyzed theoretically and experimentally investigated the absorption of sound by flat cylindrical resonators or systems of similar resonators, and found a strong increase in absorption at resonant frequencies. Absorption increases severalfold when a collar of batting is introduced around the resonator. The discussion, in which N. N. Andreev, S. N. Rzhevkin, B. P. Konstantinov, and others took part, clarified the question of the mechanism of absorption of sound by a solid resonator, which had not seemed entirely clear. The question of the absorption of resonant systems was also considered in the section of architectural acoustics in connection with the reports of S. N. Rzhevkin and M. S. Antsiferov.

B. P. Konstantinov and P. M. Bronshtein (Leningrad Electrophysical Institute) carried out a very interesting theoretical investigation on the application of the law of conservation of energy in acoustics. The authors succeeded in giving an expression for the equations of acoustics for a gas with a temperature varying as a function of the coordinates.

A detailed study of infrasonic radiators and of the propagation of infrasound was carried out by L. L. Myasnikov (Central Radio Laboratory). A theory of infrasonic radiators and receivers was developed. Data were obtained on the sound spectrum of infrasonic radiators, on the absorption of infrasonic waves in a medium, and on sound insulation at low frequencies.

The report by Prof. V. V. Shuleikin, “On the Voice of the Sea,” was heard with great interest. The author showed that, when wind passes over the surface of sea waves, infrasonic waves arise in the air (with a frequency of 8–10 oscillations per second). These waves can produce, in pilot balloons filled with hydrogen, resonant oscillations so strong that an ear placed near such a balloon feels pain. Registration of the “voice of the sea” makes it possible to predict the approach of a storm several hours in advance. The report provoked a lively discussion on the question of the origin of infrasound and on the nature of the oscillations of the balloon receiver. The possibility emerged of applying a number of technical acoustic instruments to the investigation of the “voice of the sea.”

Section of architectural acoustics. Engineer Goldberg reported on the results of measurements, by the objective method, of the frequency characteristics of reverberation from 125 to 4,000 Hz in certain Moscow halls. Until now no such data had been known, and therefore all judgments about the optimum conditions of reverberation were very poorly substantiated. It is highly desirable to obtain similar data for the best-known halls in the Union, such as: the Column Hall of the House of Unions, the Bolshoi Theater, the Great Hall of the Conservatory, and new theaters in various cities.

The work of Engineer Dreizen, concerning the theory of sound absorption in a room in the form of a rectangular parallelepiped with a nonuniform distribution of absorbers, deserves much attention. The development of Strutt’s theory for this case enabled the author to clarify the cause of the observed discrepancies between experiment and calculation by Sabine’s formula.

The reports on optimum reverberation by Dr. G. Bekesy and Prof. S. Ya. Lifshits were heard with great interest. The discussion that unfolded after the reports was exceptionally interesting and fruitful for clarifying the essence of the question. Prof. Lifshits bases the theory of optimum reverberation on the principle of constancy of the “extent” of auditory sensation (integral of the volume level \(L\) over time \(\int Ldt = \mathrm{const} = 41\) decibel·sec.) and, on the basis of his theory, finds definite values of optimum reverberation for halls of various volumes. The theory is based on the premise of a definite typical dependence of the coefficient of sound absorption on frequency, such as occurs for ordinary

of sound absorbers: fabrics, carpets, or the audience present in the hall; what is characteristic of these materials is a strong decrease in absorption at low frequencies and an increase at high ones. Békésy repeated Lifshits’s experiments and found values for ordinary materials that were likewise far from optimum. However, having created special materials (panels made of a thick layer of cotton wool covered with dense fabric), which strongly absorb low frequencies and absorb the upper ones comparatively little, and having used them to equalize the frequency characteristic of the reverberation of a room, he came to the conclusion that the optimal reverberation (for a tone of 500 Hz) proves to be incomparably lower than had been assumed, and, moreover, that it is the same for all frequencies. For a room of 2,000 m² it turned out to be about 0.8 sec., independently of frequency, instead of the 1.3 sec. obtained by Lifshits (for a tone of 500 Hz).

Among the contributions to the discussion, the remarks of Engineer G. A. Goldberg were very substantial. He pointed out that, in order to obtain the law of optimal reverberation according to Lifshits, one has to make a number of additional assumptions, significantly less probable than the initial postulate of the constancy of sound duration, namely: 1) the listener perceives a certain average value of “duration,” with the actual whole process of sound decay from fortissimo to pianissimo; 2) the power of all sound sources remains unchanged in rooms of different volume; 3) the power of various sound sources, for example voice and orchestra, is considered approximately the same; the listener determines the optimum by the sound of individual instruments, and not of their combinations; 4) for a certain volume, the optimal reverberation and loudness are considered to be established for tones of different frequencies; 5) in order to obtain optimum conditions in radio studios and motion-picture theaters, it is assumed that the loudness level in perception is 10 dB greater than in a studio or (for a motion-picture theater) correspondingly greater than in a hall of the same volume as a theater. As a result, one cannot regard as solved the problem of the optimum for large halls; further experimental work in the spirit of Békésy’s experiments is necessary.

Speaking in the discussion, I pointed out the enormous significance of Békésy’s experiments, which move the question from a dead point and make it beyond doubt that the value of the optimum reverberation, established earlier by a number of investigators, is not an absolute ideal for all conditions. It is now completely clear to us that the usual optimum has meaning only under certain typical conditions of absorption, and that a considerably better optimum can be found by using other materials for finishing rooms.

A number of works on absorbing materials have been carried out by the acoustics group of the House of Sound-Recording Laboratory (headed by Engineer G. A. Goldberg), in close contact with the acoustics laboratory under my direction at the Physical Institute of the Academy of Sciences of the USSR. We have examined in detail the question of the conditions of sound absorption in the presence of resonant systems in a room. I have proved theoretically that, under these conditions, both an increase and a decrease of reverberation can be obtained, as well as two different reverberations superimposed on one another; these conclusions have been confirmed experimentally. Resonant systems investigated by M. S. Antsyferov (cylindrical cavities in the form of a disk on a stem) may be of great importance for creating new types of absorbing materials and for correcting the frequency characteristic of absorption.

For the most effective use of absorbing materials, it is advisable to use them in combination with resonant systems. Calculations made on the basis of Antsyferov’s experiments show that the effectiveness of use of a material can be increased in this way many times over. Measurements of absorption coefficients in a reverberation chamber by objective

by the method were first established in the Union in our laboratory, and in this way Yu. I. Shneider studied, at various frequencies, the sound absorption of a number of previously known and new materials (arborite, special panels, gypsum and asbestos boards, baika, etc.). In the work of Eng. Ter-Osipyan it is shown that thick (8–10 cm) strips filled with loose absorbing material (arborite, asbestos) may be covered on top with metal sheets with very sparse perforation (occupying a negligible fraction of the whole surface), and the material does not at all lose its absorbing properties at low frequencies (sometimes even increasing them owing to cavity resonance); at high frequencies, however, reduced absorption is obtained as a consequence of reflection from the metal. This type of absorbing material is very interesting for equalizing the absorption characteristic, since it makes it possible to compensate for the increased absorption of ordinary materials (cloth, carpets, clothing) at high frequencies.

Under the direction of Prof. Lifshits, in the laboratory of the Architectural Institute Eng. Ipatov set up a method for measuring sound absorption at different angles of incidence (after E. Meyer); this method makes it possible to find the average value of the sound-absorption coefficient under conditions of diffuse sound.

A lively discussion on a number of reports of a homogeneous character was prompted by the question of the manufacture of sound-absorbing and sound-insulating materials, the required quantities of which, in connection with the growth of specialized and housing construction in our Union, are extraordinarily great. This important branch of the national economy is still in its infancy here. Sound-absorbing and insulating materials, with a few exceptions, are not produced on the Soviet market at present, and at the present moment the development of their production is encountering a number of difficulties owing to the absence of a research base and of qualified personnel who could competently solve the problem. As a result of this situation, the relevant resolutions of the NKTP have still not been implemented. The conference passed a resolution on the necessity of organizing a permanent commission on acoustic materials for the purpose of competent consultation on questions of research and production of materials.

In the section of physiological acoustics we shall note the extremely valuable report of Prof. L. A. Andreev (All-Union Institute of Experimental Medicine). By the method of conditional reflexes the author showed that damage to the cochlea by a thin drill near the apex causes the loss of the sensation of low tones, while damage at the base causes the loss of high ones. These experiments confirm the theory of hearing developed by Helmholtz.

Very interesting work on the study of the action of electric current on the auditory apparatus is being carried out by Dr. Gershuni (laboratory of Acad. Orbeli). Reports on the adaptation of hearing and the study of the sensitivity of hearing were presented by Dr. A. I. Bornshtein (Military-Medical Institute). Prof. Kravkov (Institute of Psychology) showed that visual sensations (visual acuity, irradiation, absolute threshold, threshold of light sensation) change substantially under the simultaneous action on the ear of a strong sound. The reverse influence of light on sound perceptions is also very probable. There were absolutely no reports presented in the section on the study of the structure and analysis of speech sounds.

The reports in the Section of Physiological Acoustics and the Section on Noise Control present a picture of the insufficient development, in both quantity and quality, of work on the study of hearing and speech in our country. The individual works being conducted in a few laboratories are extremely unsatisfactorily provided for in respect to the modernity of the equipment. The work of this kind has not yet found its proper place in the system of our scientific institutes. It must be taken into account that these works are clearly complex in character and do not belong distinctly to any

Congresses and Conferences

to one of the institutes with a narrow specialty. Here what is required is a synthesis of work in physics, physiology, medicine, and technology, a fruitful form of which has not yet been found among us. The lag in this scientific field entails an especially insufficient development of work in such highly important areas as the study of hearing and speech for purposes of technical applications, the organization of the struggle against noise, the manufacture of apparatus for the deaf, etc.

In the field of combating noise, a number of practical works have been carried out in various cities, but it should be acknowledged that the scientific validity of the investigations and measurements being made is almost everywhere at an extremely low level. The measurement of hearing sensitivity is carried out in medical institutions by obsolete methods; the measurement of noise level and sound intensity is performed with instruments that give a colossal discrepancy with one another, and so on. The organization of the testing and standardization of instruments has not been set up. The resolutions adopted by the conference emphasize the extremely unsatisfactory situation in this field. One of the most important measures for putting the work of combating noise in order, according to the conference resolution, would be the organization of an All-Union Committee for Combating Noise, whose functions should include:

1. Organization and planning of work to combat noise.
2. Organization of scientific-research work along the lines of acoustic measurements, as well as the development of standards and measuring apparatus.
3. Development of norms of harmfulness and measures for control of noisy industries and street noise.
4. Collection and processing of materials on the measurement of noise in factories, on transport, in streets, and in dwellings.
5. Drafting of proposed decrees on combating noise for verification in the appropriate bodies.
6. Broad propaganda of the struggle against noise, consultation, publication of a corresponding printed organ, and organization of a permanent exhibition and anti-noise weeks.
7. Organization of the training of personnel for research and production work.

The section on combating noise heard a number of reports illuminating particular questions, among which we shall note the reports: by Engineer Sheichman on the production of hearing apparatus for the deaf; by Drs. Navyazsky and Belogord on noise harmfulness and on the organization of the struggle against industrial noise; by Engineer Vinogradov on the draft mandatory decrees on combating noise. In the latter report and in the discussion it was emphasized that there is an urgent necessity to combat the extremely widespread uncultured use of radio installations and loudspeakers among us, the noise of which everywhere disrupts the possibility of peaceful work and rest for a vast number of working people, all the more since this evil has not met with opposition in the form of corresponding mandatory decrees.

On questions of electroacoustics and sound cinema, a number of very valuable special technical reports were made, which show that in our country a great deal of interesting work is being conducted in these fields and that cadres of young workers are growing. We note the work of the acoustic laboratories of the Central Radio Laboratory of Glav-Esprom, the Cinema-Photo Institute, the Kiev Institute of Cinematography, the laboratory of Engineer Tager in Mezhrabpomfilm, the Kiev Film Factory, the laboratory of the House of Sound Recording, and others.

For all research and production organizations working in the field of acoustics, the scarcity of special measuring instruments and general acoustic apparatus is an extremely difficult circumstance. On the report of the electroacoustics section, the conference stated the absolutely unsatisfactory situation with the production of measuring acoustic apparatus, the scattered nature of the work of various organizations in this field, and the absence of the principal measuring apparatus on the market, or only apparatus of inadequate quality.

satisfying the requirements of scientific-research work. The Conference considered it expedient to concentrate all production of electroacoustic apparatus at several large, well-equipped plants and, as soon as possible, to put into serial production the most widespread examples of microphones, loudspeakers, adapters, and special measuring instruments (such as filters, attenuators, sound generators, frequency meters, etc.). The Scientific-Research Institute of Metrology was instructed to work out an exact nomenclature of the necessary measuring apparatus and to identify the designs currently lacking that should be developed. The Conference considered it necessary to ask the Chief Administration of the People’s Commissariat of Heavy Industry to include in the production plan the necessary measuring and general electroacoustic apparatus.

The Conference devoted serious attention to the question of training personnel in acoustics. In this matter the state of affairs was recognized as unsatisfactory, and a resolution was adopted stating that in a number of branches of industry, as well as in institutes and laboratories, there is an acute need for specialists in acoustics, especially acoustical physicists, and for a whole range of specialists with a narrower technical orientation; and this need is not at all covered by the present availability of qualified specialists. The teaching of acoustics at a number of higher educational institutions is in an unsatisfactory state because of the lack of qualified teaching personnel, the insufficiency of the time allotted, the absence of specialization and, correspondingly, of developed programs, and, chiefly, because of the lack of proper equipment in teaching laboratories. Planning for the training of acoustics personnel has not hitherto been carried out rationally. In the opinion of the Conference, this task should be resolved by a special interdepartmental commission, whose functions will include the quantitative determination of the need for acoustics specialists of various profiles. The resolution notes the need for acoustics specialists of the following types:

a) acoustical physicists, possessing good training in mathematics, mechanics, and theoretical physics, and also mastering the methods of physical, acoustical, and electro- and radio-engineering measurements, both absolute and comparative. It is expedient to train specialists of this type in the physics faculties of universities, and also in the engineering-physics faculty of the Leningrad Industrial Institute. A necessary condition meeting the present high requirements for the level of training of acoustical physicists is the radical reconstruction and organization of new laboratories in the field of special acoustical measurements, as well as the establishment of departments of acoustics.

b) acoustical engineers, having sufficient training in the field of general and special technical disciplines and special training in the field of theoretical and applied acoustics with a specialization in one of the acoustical disciplines (electroacoustic apparatus, radio broadcasting, telephony, gramophone recording, sound cinema, hydro- and aeroacoustics, sound-absorbing materials, architectural acoustics, noise control, medical acoustic apparatus, musical instruments, etc.).

The situation is quite unsatisfactory with the training of personnel in physiological acoustics, noise control, architectural acoustics, and in the line of acoustics of musical instruments, where comprehensive training is required in fields of knowledge sharply different in character, for example music, physics and technology, or physiology, medicine, and physics. The problem of training such “complex specialists” can apparently be solved through special postgraduate study after graduation from higher educational institutions.

In conclusion, the Conference was faced with the question of the necessity of uniting work in the field of acoustics on an all-Union scale.

The conference revealed the broad scale and the wide variety of fields in which work on acoustics is now being conducted. At the same time, it became clear how closely related these diverse branches are, and how much they need constant communication and the organizational, scientific, and industrial support of one another. Proceeding from these considerations, the conference deemed it necessary to create an All-Union Association of Scientific Research in Acoustics. In order to establish the association, it was resolved to appeal, through the Physics Association of the People’s Commissariat of Heavy Industry, to the Academy of Sciences of the USSR. The implementation of this resolution was entrusted to a commission consisting of: Prof. N. N. Andreev, S. N. Rzhevkin, P. N. Belyakov, S. Ya. Lifshits, Docent L. D. Rozenberg, and Engineer K. A. Gladkov.