Chronicle

Expanded Meeting of the Acoustics Commission of the USSR Academy of Sciences

From February 25 to March 1, 1949, an expanded meeting of acousticians took place in Moscow, convened by the Acoustics Commission under the Division of Physical and Mathematical Sciences of the USSR Academy of Sciences. The purpose of the meeting was to illuminate the paths of development of Soviet acoustics both in the past and for the future.

The meeting was attended by 138 people representing 56 research institutes and various organizations. With great interest and exceptional activity, the meeting heard and discussed reports by Soviet acousticians on various sections of acoustics, such as: ultrasonics, electroacoustics, architectural and building acoustics, sound reinforcement, acoustics of motion-picture filming and film projection, and acoustic measurements. In all, 17 review papers were delivered and 10 communications were made on them.

It was noted that after the Great October Revolution, an enormous number of theoretical and experimental works had been created in the field of acoustics, directed toward the immediate needs of the socialist economy, culture, and defense of our motherland.

The most important branches of acoustics—ultrasonic flaw detection, sound cinematography, the acoustics and sound reinforcement of large halls, the acoustics of moving media, physical studies of musical instruments, the theory of speech intelligibility, the optics of sound rays, and others—owe their origin and development to Soviet scientists.

As a result of the selfless labor of Soviet scientists and specialists, both in the prewar years and especially during the years of the Great Patriotic War, domestic acoustics occupied one of the foremost positions in world science and, in many branches, has priority and a leading role both with regard to the method of solving problems and to the practical results obtained.

At the meeting, a whole series of facts was established showing that the priority of Russian and Soviet physics in various fields of acoustics is stubbornly hushed up in the foreign press.

Opening the meeting, Corresponding Member of the USSR Academy of Sciences N. N. Andreev noted that the source of the successes of Soviet acoustics is the unprecedented scope in history of the national-economic works of Stalin’s Five-Year Plans. Thus, the development of Soviet architectural acoustics was conditioned by the creation of such unprecedented structures in scale as the Moscow Central Radio Broadcasting House, the Central Sound Recording House, and the Palace of Soviets, which posed before acousticians a number of practical and theoretical problems, the solution of which

could not be drawn from ready-made domestic and foreign experience. He emphasized the organic connection of the scientific investigations carried out by Soviet acousticians with Russian physical science, which has always been distinguished by the breadth of its coverage of the phenomena studied, by a profound physical understanding of the processes taking place, and by originality. N. N. Andreev pointed out that the conference could not hear survey reports on all branches of acoustics and that the further work of the Acoustic Commission would include the drawing up of plans of works, into which, along with the survey reports and communications already heard, there would also enter those that would additionally be sent to the Acoustic Commission on questions of the development of Soviet acoustics.

At the first session of the conference a major report by S. Ya. Sokolov, “The Development of Soviet Ultrasonic Defectoscopy,” was heard.

The defectoscope was first proposed by the speaker in 1927 in the Soviet Union. Until 1934 the method of illuminating sheet steel with a stationary sound was used. Disturbances due to multiple reflections from the boundaries of the sheet and the liquid medium led, in 1935, to a transition to illumination by separate pulses, with intervals sufficient for the damping of reflections. In 1940 pulse apparatuses with high resolving power were already developed and found wide application. The use of achievements of radiolocation in the field of pulse technique made it possible, beginning in 1942, to shorten the pulse to 2 microseconds and to improve the instrument, although it is complex in construction, but distinguished by high effectiveness and simple operation. The speaker noted that further improvement should proceed by shortening the pulse to \(1/2\)—\(1/4\) microsecond and increasing the carrier frequency (at present 5 megahertz). A fundamentally new method of defectoscopy is the obtaining of sound images, analogous to what is done in an ordinary microscope. In connection with this, investigations are being carried out on the sound conductivity of crystals and metals at frequencies of the order of \(10^8\)—\(10^9\) hertz. It has been found that the attenuation of sound in metals is connected chiefly with microinhomogeneity, which, in particular, explains the observed good conductivity of sound by homogeneous crystals. Anisotropy of the conductivity of ultrasound by quartz has been observed, the conductivity in the direction of the optical axis being the greatest. A model of an acoustic microscope has been made in which the receiver is a quartz plate serving as the bottom of a cathode tube. With the aid of an electron beam scanning the surface of the quartz plate inside the tube, it proves possible, using television apparatus, to obtain on the receiving cathode tube a contour corresponding to the configuration of the ultrasonic field. In this way, at a frequency of 10 megahertz, an image was obtained of a loop made of wire \(0.35\) mm thick and placed near the quartz plate. Defectoscopic methods of observation may find application in measuring temperatures, rates of chemical reactions, studying inhomogeneities of liquids, etc.

In the report “The Development of Work on Sound-Focusing Systems,” L. D. Rozenberg noted the priority of Russian scientists in this field. The first thorough qualitative work on the sound lens was carried out and reported, together with a demonstration of the lens, at a meeting of the Russian Physico-Chemical Society in 1889 by the physicist N. A. Gezehus. Fine ebonite shavings filling a metallic spherical mesh formed a porous medium in which the speed of sound was less than in air. The source of sound was a bird call, and the indicator was a sensitive flame.

The first experimental study in the world of the fine structure of a diffraction sound “spot” was carried out by K. A. Leont’ev

(1925), with an objective receiver—an electromagnetic telephone of small dimensions operating on a galena detector. With it, the distribution of sound pressure in the focal spot of a parabolic mirror was studied, and the first and second maxima of the sound spot were detected. L. Ya. Gutin, proceeding from Green’s general formula, gave expressions for the amplification coefficient and the distribution along the axis, and the characteristic of the directivity of a parabolic mirror. The speaker obtained simplified formulas for paraboloids with aperture angles greater than 90°. G. D. Malyuzhinets solved the problem of the diffraction of sound by a zone plate, obtaining simple expressions suitable for calculation. Experimental studies of the focusing of parabolic mirrors and zone plates, carried out in the Acoustics Laboratory of the Lebedev Physical Institute of the Academy of Sciences (A. A. Karatseev, B. D. Tartakovskii, and the speaker), gave good agreement between the distribution of sound pressure in the focus and theory.

The speaker calculated the transparency of acoustic lenses, taking into account the difference of phase shifts of reflections from the boundaries across the thickness of the lens, and showed that the requirements of refraction and transparency are uniquely determined by the modulus of elasticity and density of the lens material. A convenient nomogram for calculation was constructed. Calculation of the aberration of concave collecting lenses showed that their spherical aberrations are an order of magnitude smaller than those of convex lenses with the same focal length and radius of curvature (B. D. Tartakovskii). Calculation of the sound field in the focus of a concave radiator, taking account of attenuation in the medium, gave good agreement with experimental data (A. I. Gubanov).

I. E. Goron reported on the experiment of restoring recordings of speeches by V. I. Lenin, made by the only technically imperfect acoustic method available at that time (1919–1920). The unsatisfactory characteristics of the acoustic method of recording (strong linear and nonlinear distortions and high noise levels), as well as the deterioration of the matrices due to mass pressings, made it necessary to restore the recordings and improve the matrices. To reduce the noise level of the recordings, engraving treatment of the sound groove was first carried out. Then a re-recording was made using a noise suppressor whose pass band was controlled by the signal level. To restore the natural timbre of Vladimir Ilyich’s speech, the frequency characteristic of the acoustic recorder was reconstructed (for this purpose, the frequency characteristic of the recording and the frequency characteristic of a voice of the same speech pitch as V. I. Lenin’s voice were compared by statistical octave analysis), after which the speech was re-recorded with frequency correction that corrected the deficiencies of the frequency characteristic of the original acoustic recording method, as well as the distortions that arose in the technological processes of matrix manufacture. By varying the resultant frequency characteristic within small limits around the obtained value and taking into account the qualitative assessment of people who remembered V. I. Lenin’s voice, it was possible to obtain final versions of the recordings that gave the greatest approximation to V. I. Lenin’s voice. Work continues on further improving the recording of V. I. Lenin’s speech, in particular on eliminating nonlinear distortions. The corrected recording of V. I. Lenin’s speech, demonstrated to the participants of the meeting, received high praise.

In the report “Physical Studies of the Sounds of Russian Speech”, L. L. Myasnikov pointed out that Russia has priority in the study of the sounds of speech, first carried out in connection with a competition announced by the St. Petersburg Academy of Sciences in 1779 for the study of the vowel letters of speech and the artificial creation of these sounds.

The first detailed studies of the sounds of Russian speech (the singing voice) were carried out by V. S. Kazanskii and S. N. Rzhevkin, who used

an acoustic oscillograph, developed earlier by V. S. Kazanskii on the model of the mechanical oscillograph of P. N. Lebedev. Subsequent work on the development of electroacoustic measurements prepared the basis for work on the study of the sounds of Russian speech (N. N. Andreev, A. I. Belov, I. G. Rusakov, L. S. Freiman, M. I. Rodman, I. T. Sokolov, R. L. Volkov, Ya. M. Gurevich, and others).

However, the significance of this problem was not then sufficiently recognized, although it was also emphasized by S. N. Rzhevkin (the book Hearing and Speech in the Light of Contemporary Physical Research).

In 1946, in connection with the development of a method for compacting communication channels by transforming telephone frequencies, Russian speech vowels were investigated, a synthesis of vowels was carried out, and phonograms of natural and artificial speech were compared with good agreement (M. Ya. Kalner). The first studies of Russian speech were conducted at the NIRFI in 1937–1941. These include works on the analysis of Russian vowels and consonants and on the synthesis of speech sounds. In 1937 the speaker developed for the first time a method for the objective automatic recognition of speech sounds. Abroad, analogous developments appeared only 7–8 years later; the recently published method of “visible speech” in the USA belongs to this problem. The speaker emphasized the urgent need to carry out a comprehensive physical study of the sounds of Russian speech, as well as of the speech sounds of other peoples of the USSR.

In the report “Domestic Work on the Theory of Speech Intelligibility,” Yu. S. Bykov noted the work of S. I. Tetelbaum and his collaborators on improving speech intelligibility in the presence of noise. Similar methods proved very effective, and at present they are widely used in communications engineering. Fruitful work was carried out by L. A. Varshavskii, A. G. Elsnits, V. N. Fedorovich, and others on the development of methods for calculating speech intelligibility in the presence of noise, and by L. L. Myasnikov on the development of high-frequency apparatus for communication in the presence of high noise levels. The works of G. S. Sidorov were devoted to the investigation of the influence of amplitude limitation on speech intelligibility and to certain related questions; the results of the work were successfully used in the design of communication lines. He also carried out work on adapting existing articulation tables for Russian speech.

During the Great Patriotic War, the efforts of Soviet scientists and engineers were directed toward the swiftest possible solution of problems in improving the quality of communications (V. N. Fedorovich, I. M. Litvak, M. Ya. Gol’din, A. K. Lidikh, M. A. Sapozhkov, Ya. T. Kosinchuk, V. P. Il’inskii, O. V. Belyavin, S. I. Popov, and others).

In recent years, work on the theory of speech intelligibility has undergone especially great development. In 1944 I. G. Mamonkin carried out an approximate determination of the constants of Russian speech and proposed a method for calculating speech intelligibility for flat noise audiograms. In 1945 Yu. S. Bykov drew attention to the optimal characteristics of communication lines and developed a method for calculating speech intelligibility in any communication lines for audiograms of arbitrary form. In 1946 he also developed a general theory of speech intelligibility taking into account electrical and acoustic interference and nonlinear distortions. On the basis of the practical realization of this work it proved possible to improve the quality of communications in all important lines.

The speaker convincingly showed that the works of Soviet scientists on a number of the most important sections of the theory of speech intelligibility (the works of S. I. Tetelbaum, L. L. Myasnikov, Yu. S. Bykov) outstripped the achievements of foreign scientists.

In the report “The Development of Musical Acoustics in the USSR,” A. V. Rimskii-Korsakov considered the development of research on musical-

... instruments, without touching on questions of music theory, which belongs chiefly to the field of art.

The production of musical instruments developed in the USSR only after the Great October Revolution, although even before the revolution musical craftsmen were known in Russia—for example, the violin maker Lehmann, the maker of folk instruments Nalimov, the world-famous craftsman I. Batov, and others.

The organized development of the work of N. N. Andreev at the Scientific Research Institute of the Music Industry took place in 1936–1937, with his leading role, in studies of the physics of musical instruments, their design, and the technology of their manufacture. N. N. Andreev established the connection between the modulus of elasticity, density, and damping of wood and its suitability for soundboards. It turned out that the efficiency factor, so to speak, of a soundboard depends on the ratio of the modulus of elasticity to the cube of the density of the material from which it is made, which determines the choice of whether it is applicable for soundboards. N. I. Mironov and N. P. Kulikov, through a detailed study of the forest regions of the USSR, established the presence of the necessary species and kinds of trees for the production of musical instruments and freed the domestic industry from the need to import raw material from abroad. They also investigated the procedure for procuring wood for the soundboards of musical instruments and found a possible way, through the preliminary sorting of logs, to increase the percentage yield of usable wood severalfold. B. P. Konstantinov created a theory of the self-oscillation of a reed in an air stream, showing that self-excitation of oscillations is possible owing to the modulation of the volumetric velocity of the stream under the action of the reed’s vibrations and the reactive pressure of the stream on the reed. On the basis of this theory it is possible to give a qualitative and, to a certain extent, quantitative characterization of the self-oscillatory process in brass and wooden wind instruments and harmonicas. He also studied and proposed a calculation of the tuning of brass wind instruments, on the basis of which their rational design is possible. G. A. Ostroumov carried out investigations of the propagation of waves along the soundboard of a keyboard instrument and gave simplified methods for estimating the acoustic parameters of plucked instruments. A. V. Rimsky-Korsakov investigated the excitation of strings by the blow of the hammer of the keyboard mechanism and gave a technical calculation of the strings of a keyboard instrument, as well as a theory of sound radiation by the soundboard of a keyboard instrument, and developed a methodology and apparatus for evaluating the timbral qualities of plucked instruments. A. I. Belov experimentally investigated the properties of the soundboards of keyboard instruments and the mechanism of transmission of vibrations by strings to the soundboard. For the purposes of musical acoustics, a number of measuring methods and instruments were created: the string relay of B. P. Konstantinov, the method for taking frequency characteristics upon impact excitation by A. V. Rimsky-Korsakov; an instrument for testing gramophone membranes by A. A. Kharkevich, and others.

The speaker showed that the USSR is the birthplace of practical electronic music and of the first electronic musical instruments. The work of L. S. Termen at the Leningrad Physico-Technical Institute and subsequent work (L. S. Termen, A. S. Ananyev, V. A. Gurov, A. A. Volodin, V. L. Kreitser, A. V. Rimsky-Korsakov, A. A. Ivanov, I. D. Simonov) on monophonic electronic musical instruments led to the creation of very advanced models: the emiriton 7-bis, an instrument in which a very stable and reliable tuning was obtained, and a number of interesting musical timbres, as well as the instrument V-7.

A. A. Volodin, in his communication, touched upon questions of the design of electronic musical instruments, dwelling in detail on the electronic musical instrument V-8. This instrument makes it possible to obtain the sound of two voices, which makes possible a full-fledged performance of the entire violin literature and facilitates...

use of such instruments in large ensembles. In addition to the usual generator with a sawtooth wave form, a frequency divider was used, giving an uneven tempered scale of harmonics. This principle made it possible to obtain a good foundation for the clarinet group and to carry out octave transposition of the instrument’s tuning without changing the tuning of the main generator. The speaker also touched upon certain questions concerning the nature of musical sound, the influence of low-frequency components on the perception of musical sounds, etc.

In conclusion, the artist I. M. Vardovich performed Chopin’s “Nocturne” on the instrument B-8 and Rimsky-Korsakov’s “Flight of the Bumblebee” in a clarinet timbre. The sound quality of the instrument received a favorable appraisal from the audience.

A considerable place in the work of the conference was occupied by the consideration of papers and reports relating to the theory of calculation, design, and measurement of electroacoustic apparatus. In this important field of modern acoustics, Soviet scientists have created and developed the basic methods of theoretical analysis and calculation of apparatus, and have proposed and worked out a number of original instrument designs and methods of measurement.

In the paper “The Theory of Electromechanical Transformation,” V. V. Furduev noted the investigations of A. A. Kharkevich (the book Acoustic Apparatus, 1933, and Examples of Technical Calculations in the Field of Acoustics, 1938); the works of L. Ya. Gutin on the theory of the electrodynamic microphone (1936), the book Electroacoustics by G. A. Ostroumov (1936), and the investigations of V. S. Grigoriev on the theory of conical electrodynamic loudspeakers, emphasizing that the striving to systematize and enrich the general laws made it possible for Soviet scientists to create a theoretical discipline—analytical electroacoustics. In the USSR a uniform method was developed for constructing electromechanical analogies (A. I. Belov, A. A. Kharkevich, L. A. Varshavsky, and V. N. Fedorovich, G. A. Gamburtsev). The theory of electromechanical transducers developed in two directions: 1) consideration of an electroacoustic device as a generalized electromechanical four-terminal network, based on reciprocity relations (A. A. Kharkevich, Theory of Transducers, 1946–1948), and 2) application of the methods of analytical dynamics to the consideration of electromechanical systems. The first attempt at an extended application of the second concept was made by N. N. Andreev (Physical Dictionary, 1936), who showed the conditions under which ordinary symmetrical reciprocity is replaced by a somewhat distinctive form of antisymmetrical reciprocities.

The speaker noted the fruitfulness of applying the methods of analytical dynamics in the theory of electrical machines (the theory of parametric converters of Acad. Mandelstam and Acad. Papaleksi, published posthumously in 1947), in the theory of complex electrodynamic loudspeakers (the dissertation of F. A. Postnikova), and others. A general substantiation of the electrodynamic application of Lagrange’s theory and the limits of its application were given by the speaker (dissertation, 1946). On this basis, a general theory of the electromechanical coupling of linear and nonlinear systems was obtained (the book Reciprocity Theorems, 1948). The combination of both methods—the calculation of the coefficients of a four-terminal network on the basis of the electrodynamic Lagrange equation, followed by the compilation of the equations of the electromechanical four-terminal network—opens up new possibilities for the calculation of electromechanical transducers (the theory of G. N. Stal’s electromagnetic recorder).

V. V. Furduev pointed out that the calculation of piezoelectric and magnetostrictive transducers, proposed by N. N. Andreev in 1928 and subsequently developed by A. A. Kharkevich, I. G. Rusakov, and L. Ya. Gutin, still remains outside both of the above-presented statements of the general theory of electromechanical transducers.

Chronicle

The speaker stated that in the works that have appeared recently in America on the application of electromechanical feedback, the first and only study of the general theory of negative electromechanical feedback, carried out by V. S. Grigor’ev and the author in 1940, is being suppressed.

M. I. Karnovskii reviewed the principal works in the field of the directional properties of radiators and receivers.

In addition to generally known criteria for evaluating directivity, a new criterion was introduced which proved very fruitful—the concentration coefficient (Yu. M. Sukharevskii).

The evaluation of directivity as a function of the angle of the maximum absolute instantaneous value of the potential (A. A. Kharkevich) made it possible to generalize the concept of directivity to nonstationary processes as well. The concept of the “stability” of a directivity characteristic (M. I. Karnovskii) made it possible to assess the operation of directional systems over a frequency range.

Careful experimental investigations of the directivity characteristics of horn loudspeakers showed their relation to the parameters of the horn and made it possible to design an exponential horn with a frequency-independent directivity characteristic (Yu. M. Sukharevskii).

A study of the directional properties of spherical and elliptical radiators (M. I. Karnovskii) showed that, with a certain distribution of radial velocity over a sphere, it is possible to obtain a similar distribution of potential on any distance from the sphere (in some cases exactly, and in some cases approximately), which makes it possible to create a practically constant directivity characteristic over a fairly wide frequency range. For an elliptical radiator (and a flat one) such similarity is not obtained.

S. A. Makov showed the possibility of obtaining highly, practically frequency-independent, directional low-directionality systems by using the principle of multiplication of the directivity characteristics of dipole radiators and the principle of the difference of the directivity characteristics of low-directionality systems.

The speaker noted that in Olson’s work, published in the journal of the American Acoustical Society for 1946, the system proposed by S. A. Makov in 1940 is presented, although the author (S. A. Makov) is not mentioned, despite the fact that his work had been printed in such a widely circulated journal as the Reports of the Academy of Sciences of the USSR.

Of exceptional theoretical and practical interest is the investigation of the sound field of piston radiators (including their directivity characteristics): of an oscillating piston in a half-space, carried out by L. Ya. Gutin in 1937. L. L. Myasnikov considered the operation of an oscillating piston in a finite baffle and found that, when the dimensions of the baffle are small compared with the wavelength, the directivity is determined mainly by the dimensions of the baffle. Directional systems with excitation decreasing toward the edges were considered by M. A. Sapozhkov, who showed that, with an appropriate distribution of the excitation intensity, it is possible to obtain highly directional systems with small side lobes.

L. A. Varshavskii reported methods for calculating multiresonant electroacoustic systems, noting that the high sensitivity of these systems accounted for their application in wired communications. A number of works were devoted to the calculation of these systems, providing a uniform frequency characteristic in a specified frequency range: construction of a telephone system on the filter principle (A. I. Danilevskii, VEI), introduction into the telephone system of an additional acoustic mass

...and active resistances, ensuring the smoothing of resonance peaks while maintaining sufficiently high sensitivity (I. M. Litvak, the Krasnaya Zarya plant), calculation of a three-resonance oscillatory system of carbon microphones (V. N. Fedorovich, Krasnaya Zarya).

The speaker outlined a scheme for designing oscillatory systems, the essential point of which is such a choice of the analytical expression for the frequency characteristic that it satisfies the requirements imposed on it and at the same time ensures the physical realizability of the system. In the case of a purely reactive system, the form of the frequency characteristic of such a system, regarded as a four-terminal network, depends entirely on the mutual arrangement of the resonance frequencies and the attenuation points; moreover, the general method for solving the problem of locating the resonance frequencies necessary for obtaining definite forms of frequency characteristics is given by the Russian mathematical school (P. L. Chebyshev, E. I. Zolotarev, and others). Representing the input (or output) resistance of the system in the form of a continued fraction expressing the ratio of the coefficients of the four-terminal network, one can determine from the elements of the fraction the magnitudes of the circuit elements; at the same time it remains possible to vary the course of the calculation in such a way as to obtain a circuit chosen for constructive considerations. From this point of view, an essential problem (partially solved) is the determination of the limits within which the magnitudes of the elements may lie for a given arrangement of the resonance frequencies.

In the report “Acoustic Apparatus”, V. K. Iofe described the history of the development of electroacoustic apparatus (microphone and loudspeaker) in the USSR, dividing it into three stages: 1924–1930, 1930–1941, and the postwar period. The first period is characterized by the need to satisfy the requirements of nascent radio broadcasting at a still low level of production of electroacoustic apparatus and with a small volume of research work. The second period is associated with the intensive growth of production of all types of electroacoustic apparatus, which supplied the country’s needs with domestic apparatus, and with extensive scientific-research work that yielded especially large results in the calculation of apparatus. The postwar period is characterized by the rapid growth in the production of varied high-quality apparatus; research work is directed mainly toward improving the quality of sound. Among the numerous references to individual scientific works in the field of electroacoustic apparatus, the speaker named the first works on condenser microphones (Yakovlev and Shaposhnikov, 1926–1927), the study of the electromagnetic loudspeaker (A. A. Kharkevich, 1928), and works carried out in the acoustic department of the TsRL, the acoustic laboratory of VEI, later at NIKFI and TsNIIS in 1930–1941, as a result of which condenser, ribbon, and dynamic microphones and dynamic loudspeakers were developed.

The creation of the theory of the condenser microphone (R. L. Volkov, 1935), methods for calculating electrodynamic microphone and piezoelectric apparatus (L. Ya. Gutin, 1936, 1941), methods for calculating the ribbon microphone (A. A. Kharkevich, 1933, 1937), the classification of microphones and methods for calculating unidirectionally directed microphones, the limiting sensitivity of microphones (V. K. Iofe, 1938), and the theory of the higher-order gradient microphone (S. A. Makov) greatly determined work in the field of microphones.

Works by A. A. Kharkevich, Yu. M. Sukharevsky, V. E. Panteleev, R. L. Volkov, L. D. Rozenberg, V. V. Furduev, V. S. Grigoriev, P. E. Shifman, A. T. Prokhorov, A. I. Indlin, B. I. Mozzhevelov, K. A. Lamagin, S. A. Makov, F. N. Trotsievich, and many others were devoted to questions of the theory and design of loudspeakers.

Chronicle

Among postwar works, the speaker noted the development of diffuser loudspeakers, dynamic and ribbon microphones at IRPA, piezoelectric loudspeakers and microphones at TsNIIS (P. V. Anan'ev), research on the efficiency of loudspeakers (F. N. Trodevich), and the development of small-size horn loudspeakers at LIKI (M. M. Svyadoshch).

At the meeting a two-channel sound-reproducing installation with high quality indicators, developed at NIKFI (A. A. Khrushchev, I. M. Bolotnikov, A. S. Matveenko, V. V. Furduev, and others), was demonstrated.

In his introductory remarks, the head of the work, A. A. Khrushchev, reported that the technique of sound reproduction for motion pictures, developing in our country independently of foreign technology, had grown into a large branch of engineering. The newly developed system is distinguished by separate reproduction of the high- and low-frequency components by two independent channels from the input of the amplifier path to the air, as well as by the creation of the necessary reserves of peak power (up to 100 W) with very small linear and nonlinear distortions in the range from 40 to 10,000 Hz. The new apparatus surpasses the best American models. It is intended for high-quality reproduction of sound in large movie theaters and auditoriums.

The meeting noted with satisfaction the high sound quality of the developed system with various reproduced material (speech, singing, symphonic and wind orchestras).

For the creation of a new sound-reproduction system that ensured high sound quality in the demonstration of motion pictures, the authors of the work were awarded the Stalin Prize.

I. G. Rusakov illuminated the significance of the works of Russian scientists in the development of methods of acoustic measurements. In Russia, the classic investigations of N. A. Umov were carried out; he introduced the vector of energy flow (subsequently named after him) and thereby defined the concept of sound intensity and the flow of acoustic energy. P. N. Lebedev applied the Rayleigh disk to the measurement of sound intensity soon after its appearance at the end of the nineteenth century. V. D. Zernov, whose name in the world literature is associated with the absolute measurement of sound intensity, showed (1908) the suitability of the Rayleigh disk for absolute measurements and determined the accuracy of these measurements (1%). V. Ya. Altberg worked with a pressure apparatus in which nonlinear quadratic radiation pressure is used to measure sound intensity. The speaker noted the measurement work carried out by Soviet scientists. A careful study of the applicability of the Rayleigh disk for the calibration of measuring instruments was conducted by Yu. N. Egorov (1939). L. S. Freiman and the speaker (1931) tested the operation of the Rayleigh disk with impulsive sound and showed its applicability for this purpose. Measurements of displacements by the speck method and modifications of this method were proposed and tested by N. N. Andreev (1927). Absolute measurements of sound oscillations in water with the use of radiometers were carried out by I. T. Sokolov. The development of a measuring microphone and an acoustic probe was carried out in 1935 at the Krasnaya Zarya plant by L. A. Varshavskii; at present the development of measuring microphones is under way: a dynamic one at IRPA (V. K. Iofe) and a piezoelectric one at TsNIIS (P. V. Anan'ev). Among the numerous methods of calibrating microphones, the speaker dwelt on the method, little covered in the literature, of calibrating a capsule microphone, developed by N. D. Spiridonov (with pressure supplied from a Pitot tube, which made it possible to eliminate the influence of the observer’s presence), and on absolute calibration by the reciprocity method; the speaker noted that these calibrations are based on theoretical reciprocity relations formulated by N. N. Andreev as early as 1935–1936.

Soviet acousticians have created a number of instruments that automate measurements, for example the analyzer of M. I. Rodman and others. Measurements in the field of physiological acoustics made it possible to determine the unit of natural loudness (S. N. Rzhevkin and A. V. Rabinovich). The speaker also briefly dwelt on works on acoustic measurements by A. I. Belov, M. I. Rodman, L. L. Myasnikova, B. P. Konstantinov, and many others.

M. V. Kazantseva described the work on the absolute calibration of microphones by the reciprocity method, carried out in the Acoustic Laboratory of the Physics Institute of the Academy of Sciences. A method has been developed for calibration by pressure using the reciprocity method in a tube, which has advantages over the known earlier method of calibration in a chamber small in comparison with the wavelength (accuracy, absence of the influence of resistances connected to the chamber or tube, possibility of attaining higher frequencies; the limiting frequency in a tube corresponds to \(\lambda=\dfrac{d}{2}\), in a chamber—

\[ \lambda=\frac{d}{4}. \]

). The result of calibrating a piezoelectric microphone was obtained with a probable error of \(0.4\%\) (\(0.05\) db).

In the communication of A. A. Yampolsky on the application of the reciprocity theorem to the absolute calibration of electroacoustic transducers, the results of work of IRPA for 1947–1948 were presented. Noting that the theoretical part of the work contains a direct proof of the reciprocity theorem and the derivation of calibration relations in a free field, taking into account the reverse influence of the transducers on one another, as well as for various modes of tube operation (some of which are already known), A. A. Yampolsky dwelt on the results of experimental investigations aimed at creating a practically convenient, generally accessible method of absolute calibration. For the investigations, ordinary microphones and transducers with dimensions from \(1.8\) cm to \(30\) cm were taken as objects. Experimental comparison of these transducers in a chamber, and also in a tube, showed that the accuracy of calibration amounts to tenths of a decibel. It turned out that the calibration results do not depend on the distance between receiver and emitter, if it is not too small. The possibility was shown of calibration in a non-damped ordinary laboratory room, provided that the distance from the electroacoustic transducers to the nearest reflecting surface is 10–15 times greater than the distance between them (the nonuniformity of the field due to reflections does not have an effect). The accuracy of the method at medium frequencies is \(0.6\) db, at low frequencies \(1.5\) db.

In the major report “The Development of Soviet Sound Cinema,” P. G. Tager, presenting interesting factual material, showed the major role of Russian scientists and inventors in the creation of the photographic method of recording and reproducing sound, the only one of significance for cinematography. He noted the following most important inventions: photographic sound recording (A. Vikstsemsky, 1889), the photoelectric method of reproducing a phonogram (I. Polyakov, 1910), a method of recording and reproducing sounds (Ya. Gize, 1912), and another method of recording sounds (V. I. Kovalenkov, 1922). P. G. Tager recalled that the first recording of sound on film in Russia was made by S. Ya. Lifshits as early as 1910.

The speaker emphasized the enormous importance for sound cinema of A. G. Stoletov’s investigations in the field of the photoelectric effect (1888), who created the world’s first photocell and developed a circuit for connecting a photocell, essentially identical with the modern one, and of the inventions of A. S. Popov, without whose further development modern sound cinema would have been impossible.

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In 1926 in Moscow, under the author’s direction, a group began work which succeeded in creating an original system of sound cinema, using for light modulation the phenomenon of double refraction in dielectrics placed in an electric field, and recording the sound in the form of an intensity phonogram.

In 1927 in Leningrad, work began under the direction of A. F. Shorin which led to the creation of another original system, using as the light modulator a single-string oscillograph and sound recording in the form of a transverse phonogram. In 1929 V. D. Okhotnikov, A. G. Mashkovich, and others built a sound-recording apparatus on yet another principle.

Among subsequent works, the speaker cited the development of a noiseless phonogram (N. D. Smirnov), the establishment of the regime for photochemical processing of phonograms (S. S. Shushurin), work on multi-sound recording (A. I. Parfent’ev), the study of the mirror galvanometer (V. A. Burgov and A. M. Melik-Stepan’yan), the development of two-link amplifiers and loudspeakers (A. A. Khrushchev and others), and a number of other works.

The principal scientific and technical problems at the present time are: the creation of a phonogram for color cinema, stereophonic sound reproduction, and also research in the field of new light modulators.

A report by I. E. Goron, “Domestic designs of apparatus for magnetic sound recording,” was heard with great interest.

The first apparatus for magnetic sound recording on wire was developed in 1930 at VÉI by V. K. Vitroskii. In 1938 a reverberator based on the principle of magnetic recording was made (V. S. Kazanskii). In 1940 a rehearsal apparatus was developed in which the tape is wound into a continuous skein (I. S. Rabinovich). In 1944 a series of line apparatuses was produced, in which recording is carried out by lines with a spacing between them of 0.5–0.6 mm across a tape 35 mm wide. In 1944 the development of a line apparatus on a tape 200 mm wide was begun, making it possible to have recording on tapes (I. S. Rabinovich, A. F. Malyutin, B. P. Matveenko, G. I. Keller, and S. S. Myl’nikov). In 1943, at the Scientific Research Institute of Sound Recording (I. E. Goron, A. A. Vroblevskii, G. B. Ketov, V. I. Parkhomenko, D. I. Porto, A. E. Smirnov, E. Ya. Ditssin), development began of a series of apparatuses operating on ferromagnetic film 6.5 mm wide. The first of these, the apparatus of type MAG-1, operated at a speed of 456 mm per minute. In 1946 an apparatus with the same kinematic scheme, with ultrasonic biasing (type MAG-2), was developed. These apparatuses were produced at two factories. The drawback of the rewinding of the MAG-1 and MAG-2 apparatuses was eliminated in the correspondent apparatus MAG-3. MAG-4 is distinguished by a special simple design—by the absence of cassettes. The speed is 400 mm per minute; the recording duration is 20 minutes. The dynamic range is 30 db. The design of the MAG-6 makes it possible quickly to change cassettes and to work rapidly in forward motion and rewinding.

The speaker noted that the main questions of magnetic sound recording—the questions of the electroacoustic device and of the magnetic system—now present no special difficulties. The greatest difficulties are caused by the design of the drive mechanism. Abroad, in addition to the main sound motor, it is customary to install additional motors to regulate tension and rewinding accelerations. However, despite the complexity of the design in three-motor apparatuses, regulation of the tape tension is insufficiently satisfactory. Therefore the series of apparatuses of the MAG type, intended for mass use, is single-motor.

The speaker recalled that in May 1947, at the jubilee session of the Popov Society, a demonstration of three-channel stereophonic—

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...disk recording, for which a 3-motor arrangement with a three-track head was used. Only a year later, in the middle of 1948, American journals published a description of such an installation. In conclusion, I. E. Goron reported on work on the theory of magnetic recording, and also raised the question of the necessity of establishing speed standards for magnetic sound-recording apparatus.

The conference familiarized itself with the design and operation of the principal types of apparatus for magnetic recording and noted their good quality.

At the conference four reports were heard in the section on architectural acoustics, showing that in this branch of acoustics Soviet scientists and engineers have achieved great successes.

In a joint report (with L. D. Rozenberg), “On the Development of Architectural Acoustics in the USSR,” G. A. Gol’dberg indicated that the first work in the world on optimal reverberation time was carried out in the USSR (S. Ya. Lifshits, 1924). In 1922–1923 the acoustic equipment of the first studio had already been produced (S. A. Zaitlenok). The centers of architectural acoustics were TsNIIS (I. G. Dreizen, S. T. Ter-Osipyants, Yu. M. Sukharevskii), the Moscow radio center (S. N. Rzhevkin). In the 1930s architectural acoustics was practiced by FIAN (S. N. Rzhevkin), the Acoustics Administration for the design of the Radio House (the speaker), NIKFI (V. V. Furuev), the Construction of the House of Sound Recording (S. T. Ter-Osipyants and the speaker), the Academy of Architecture (S. Ya. Lifshits, S. P. Alekseev and A. K. Timofeev), and then the Construction of the Palace of Soviets, which organized a large acoustics section (L. D. Rozenberg) with a laboratory and a special sound-measuring testing ground (V. S. Grigor’ev).

The speaker recalled that, before Eyring’s work containing the concept of image sources appeared abroad, it had been proposed in the works of the Soviet scientist M. V. Machinskii as early as 1930. The geometrical-statistical concepts of room acoustics were further developed by L. D. Rozenberg, M. A. Sapozhkov, G. A. Chigrinskii, who provided methods for calculating the reverberation of rooms of various shapes and with various arrangements of sound-absorbing materials.

L. M. Brekhovskikh showed rigorously that the domain of application of geometrical room acoustics is rather broad, and refuted assertions made abroad about the unsuitability of these concepts (Morse and Bolt). The acoustic design of very large halls required consideration of separate reflections from surfaces (the speaker and B. D. Tartakovskii) and investigation of the propagation of sound along absorbing surfaces (N. N. Andreev). A complete and rigorous solution of the second problem was given recently (L. M. Brekhovskikh and G. D. Malyuzhinets). The first considered propagation of waves from a point source above the surface separating two isotropic media; the second investigated the case of propagation along the surface of a material whose absorption can be described by a normal impedance. In both cases the law of decrease of sound intensity proved to be non-exponential, as had previously been believed. Questions of reverberation perception were studied with electrically generated decaying sound pulses by the speaker jointly with S. T. Ter-Osipyants. It became clear that the criterion by which subjects compare two different decaying sounds is the reverberation time (the rate of decay), independently of the difference in the initial sound intensity and frequency. Integral laws were not confirmed in these experiments. In particular, the apparent reduction of reverberation during decay with a jump (the case of a short distance between the sound source and the listener or microphone) was investigated.

The first specially developed sound-absorbing materials were arboreal board made from wood pulp (P. V. Lapshin), absorbing...

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A.P.P. plaster (S. P. Alekseev), fibrolite, penoshammot, and others. At the Asbestos Institute asbestos materials were being developed. V. A. Andreevskii and K. A. Vital proposed and developed a number of original acoustic materials.

Theoretical criteria were given for the applicability of the representation of a normal impedance (N. N. Andreev, L. M. Brekhovskikh); it was shown that porous media should be characterized, in addition to the usual constants—inertia, compressibility, and viscosity—also by the character of pore relaxation; the influence of deep cavities commonly used to increase absorption was studied (N. N. Andreev, V. Tsikunov, M. A. Sapozhkov).

In the Soviet Union two lines of work were developed in the theoretical study of the absorption of sound by materials.

The use of resonance to increase the velocity of oscillations in the throats of resonators, and as a consequence the most effective use of sound-absorbing material, was made by S. N. Rzhevkin the basis of resonant absorbers with readily adjustable frequency absorption characteristics, which were comparatively simple to treat mathematically (S. N. Rzhevkin, M. S. Antsiferov, V. S. Nesterov). L. D. Malyuzhinets, considering the sound-permeability of perforated screens, subsequently found a possibility, by successively joining several screens, of obtaining an anisotropic sound-absorbing layer and developed its theory, giving approximate methods of calculation in the high-frequency region (energetic methods) and considering the material at low frequencies as a continuous medium. By means of an impedance diagram (an impedance hodograph) it is possible to study sound absorption readily for various laws of distribution of the constants over the thickness of the layer.

L. D. Rozenberg, in a co-report, touched upon the methods of architectural-acoustical measurements and the apparatus used, pointing out that as early as 1921–1923 a reverberometer with a microphone had first been used in the USSR (S. Ya. Lifshits, S. T. Ter-Osipyants). This gave substantial advantages in comparison with the apparatus used abroad by Sabine and others, in which the receiver was the ear. In connection with the extensive construction of radio studios in 1929–1930, a precision reverberometer and an oscillograph were built, permitting the entire process of sound decay to be registered (I. G. Dreizen, S. T. Ter-Osipyants, Yu. M. Sukharevskii). In 1934, in N. N. Andreev’s laboratory at the Leningrad Electrophysical Institute, Z. I. Mityagina, with the participation of A. I. Belov and N. V. Nikol’skii, constructed an objective reverberometer consisting of a microphone, an amplifier, and a photographic recording attachment. In 1940, in the House of Sound Recording, a fast-acting sound-recording recorder was built (Z. N. Rezyakova). The speaker recalled that in 1936–1937 the Acoustics Commission, among questions of measurement technique, considered three works, two of which were devoted to the automation of measurement methods and to measurements in reverberation chambers (A. A. Kharkevich), and the third to the choice of methods for measuring reverberation time (G. A. Gol’dberg). A method of averaging measurement results, using a source possessing a continuous spectrum with subsequent band analysis, found wide application both in measuring reverberation and sound insulation (V. S. Grigor’ev). A variant of this method is the use of music or speech recorded on film (A. N. Kacherovich).

The impulse method of investigating rooms, first in the world proposed and developed in 1929 by A. I. Belov, was developed in 1940 by Yu. M. Sukharevskii, who applied it to the study of the acoustics of the Tchaikovsky Concert Hall. Measurements of four acoustic constants

materials (G. D. Malyuzhinets, Yu. P. Krashenninikov, and A. V. Makarov) preceded American studies by at least four years. Reverberation methods for measuring sound-absorbing materials have been studied, in particular with respect to the dependence of results on the size of the chamber, the material, etc. (M. S. Antsyferov, G. A. Gol'dberg, and others). Methods for measuring sound insulation are analyzed in the fundamental work of I. G. Rusakov. In the laboratory of the Palace of Soviets, universal measuring apparatus was created for measuring vibrations and noise (M. S. Antsyferov, G. A. Surin).

In the report on the acoustics of film studios and movie theaters, A. N. Kacherovich described the work of the acoustic laboratory of NIKFI. Pavilions for synchronous filming are being treated with a new sound-absorbing material developed in the laboratory in 1948 (L. M. Rosenfeld, I. A. Shlyakhter, and the speaker), consisting of a solidified foam of pale-green color, made from urea-formaldehyde resin. It is nonflammable; its density is 0.15, and its sound-absorption coefficient is 0.45–0.48 over a wide frequency range.

Acoustic conditions in sound studios (rooms for sound recording) have been studied. Sound-absorbing semicylindrical plywood panels have been created and applied. It has been shown that the criterion of acoustic conditions in a sound studio is not only the reverberation time, but also the form of sound decay. A study of the acoustic conditions of more than 40 movie theaters preliminarily established the influence of the shape of the hall, in particular the ceiling height, on the process of sound decay and the quality of the sound. It was noted that in sloping halls there is often increased resonance, despite the fact that the calculated reverberation time (according to measurements of empty halls) lies below the recommended optimum. In the speaker’s opinion, this indicates that, in addition to reverberation time, other causes also affect the assessment of the resonance of a theater.

S. Ya. Lifshits touched upon his work on the optimum reverberation and new phenomena of auditory perception, pointing out that the criterion he established in 1926 for the quality of the acoustics of a room was accepted by MacNair only in 1929, and he rejected Knudsen’s assertion that MacNair had independently established the connection between reverberation time and the law of integral duration. He also indicated that Maxfield’s works (1948) are essentially an attempt to derive the optimum reverberation from the first integral law of hearing. The speaker further reported that, as a consequence of the integral laws of hearing, he had discovered the discreteness of auditory perception and selective enhancement of auditory perception. It proves possible to increase the ear’s sensitivity to weak impulses by up to 100 times by introducing, in addition to them, a constant tone of the same frequency into the ear. A connection has been established between auditory perception and the sensation of vibrations.

In I. G. Dreizen’s report, “Sound reinforcement and sound amplification in enclosed spaces,” the role of the theoretical works of the Soviet school of physics in the analysis of self-excitation processes in systems with feedback was noted (V. M. Buxeverov, G. S. Gorelik, K. F. Teodorchik). Soviet acousticians and engineers carried out theoretical and experimental work that served as the basis of this branch of acoustics. Yu. M. Sukharevsky interpreted a sound-absorption system in an enclosed space, consisting of a microphone path and loudspeakers, as a closed chain of loudspeakers with a gradually decreasing feedback coefficient (f.b.c.) as the distance from the beginning of the chain increases. G. A. Gol'dberg developed this concept for a system of several (acoustically connected) sound-amplification paths in a single room (for example, stereophonic sound reinforcement), showing that in a fairly complex amplification system a number of values of the f.b.c. have рав-

Ю. М. Sukharevsky experimentally showed that the coefficient of direct sound in rooms corresponds only partially to the in-phase summation of sound waves emitted by the loudspeaker and reflected from the surfaces of the room. He found that the degree of unevenness of the sound field (the peak factor of the sound field) in most rooms is 2–2.5, while the permissible (imperceptible) increase in reverberation time due to feedback is 1.7.

The speaker was able to consider the acoustics of halls equipped with a sound-reinforcement system on the basis of methods of the energy-statistical theory of a closed volume, and from an energy balance equation for the room to obtain coefficients characterizing the coefficient of direct sound of sound absorption. With the aid of such an energy-statistical treatment the speaker analyzed the principal systems of nonlinear sound reinforcement and proposed for them a number of calculation formulas. Yu. M. Sukharevsky and the speaker found that the loudness level at the listener should be no less than 15 db lower than the loudness level at the speaker’s microphone.

N. N. Andreev proposed, and L. D. Rozenberg and B. D. Tartakovsky developed, a variant of sound reinforcement with the aid of a distributed system of loudspeakers, in which the listener is in the zone of action of several loudspeakers and the influence of the acoustics of the room is substantially weakened.

I. G. Leizer read a paper on the development of sound insulation in the USSR, noting the first works on sound insulation, carried out in the 1930s (S. T. Ter-Osip’yants, M. Ya. Mashonkin, I. G. Rusakov).

In the House of Sound Recording, the Television Center, and others, “floating” studios were built. The impetus for solving very complex problems of sound insulation was the construction of the Palace of Soviets. In the Acoustics Laboratory of this construction project, by the method of measuring continuous spectra (V. S. Grigor’ev), the insulation against airborne sound of various walls and floors in existing buildings and in measuring chambers was measured (V. M. Rudnik, L. A. Yakovlev). The transmission of vibrations through the building was also measured (M. S. Antsyferov, G. A. Surin, R. E. Gassko). Numerous measurements of the noise of ventilation installations (L. A. Yakovlev, E. Ya. Yudin) made it possible to create numerical characteristics of noise under various operating conditions, used for design. A. I. Belov, on the basis of a statistical concept, simplified the calculation of the sound insulation of ventilation installations and gave engineering formulas, differing from those proposed abroad in rigor of derivation and simplicity of application. Measurements were made of the noises of urban transport (V. S. Kazansky, K. N. Shabtshev, S. P. Alekseev). The construction of high-rise buildings in Moscow is conditioning the further development of scientific work in the field of sound insulation carried out by the laboratories of the Construction Administration of the Palace of Soviets and the All-Union Academy of Architecture.

In M. S. Antsyferov’s communication, “Some applications of vibrometry in acoustics,” the results were presented of simultaneous measurements of noise and vibrations penetrating into a building through structural elements from outside, carried out in 1939–1941 by the laboratory of the SDS (L. A. Yakovlev, G. A. Surin, R. E. Gassko and the speaker). As a result of these measurements a simple relation was established between the levels of noise and vibration; this relation can be used in the study of the insulation of multilayer walls, in calculations of the noise level in buildings from data of measurements of structures not yet completed, and so on. The degree of agreement of the results of independent measurements of airborne noise and vibrations can be improved by taking into account the absorption of the room.

S. P. Alekseev spoke about street noises and methods of combating them. He presented data from measurements of noise in the streets and squares of Moscow at various times of day, as well as measurements made

in a metro car. It was found that the minimum noise has a constant character, depending on the district and the character of the place. The maximum noise is determined by the movement of transport. On the basis of the measurements, conclusions were drawn concerning the necessary measures for reducing urban noise (wide streets, not very high building development, greenery, good paving of roadways, reduction of traffic noise).

G. L. Navyazhsky’s report, “The Struggle against Industrial Noise in the Soviet Union,” was devoted to the history and present state of this question. The achievements of Russian science in the study of the influence of noise on the organ of hearing were shown (S. F. Shtein, N. F. Popov), as was the development of scientific work in this direction after the October Revolution (more than 220 works have been completed; a laboratory of the Leningrad Institute for Labor Protection of the All-Union Central Council of Trade Unions has been organized, as have the laboratory of physiology and pathology of hearing of VIEM, and others). Instruments have been created for measuring the harmful effect of noise with allowance for increased harmfulness at high frequencies (this feature of noise was established by Soviet scientists V. G. Ermolaev, G. L. Navyazhsky, A. V. Zakher, A. I. Bronshtein, and others); permissible noise levels have been investigated (V. G. Ermolaev, G. S. Tramvitsky, G. L. Navyazhsky); it has been proved (A. F. Popov, V. G. Ermolaev, G. L. Navyazhsky) that the influence of intense sounds is not based on “trauma,” but on a disturbance of adaptation, and that physiological neutralization of the pathological consequences that occur in the auditory organ under the influence of a disturbance of adaptation can be achieved (G. L. Navyazhsky) by the method of “disinhibition” in accordance with the teaching of Academician I. P. Pavlov.

Extensive work is being carried out on the radical silencing of production processes (for example, replacement of electric-welding cells, reduction of the noise of electric machines and fans by changing the shape of the blades, reduction of the sounding surface of cleaner drums, etc.).

Special apparatus has been developed for improving the audibility of conversational speech in noisy workshops.

I. I. Slavin reported that, in order to improve the intelligibility of speech under conditions of a high noise level, it is advisable to attenuate the low-frequency part and to raise the high frequencies of the amplification path intended for reproducing speech in industrial premises with a high noise level, since the most important frequencies for speech intelligibility are those from 600 to 2200 cycles.

B. P. Konstantinov shared with the participants of the conference recollections of the outstanding Russian acoustician A. I. Belov, who perished during the siege of Leningrad, and spoke about his principal works in the field of acoustics. A. I. Belov created a string frequency meter of unsurpassed accuracy, developed a methodology for measuring acoustic resistances, studied the theory of acoustic transducers and electromechanical analogies, was the first to investigate the vibrations of turbine blades in the frequency range up to 20,000 cycles, and created acoustic measurement methods, making extensive use of the sand method proposed by N. N. Andreev.

A. I. Belov gave an exhaustive calculation of the tuning of the clarinet and brass wind instruments, developing a method of equivalent lengths that makes it possible to construct the scale of an instrument with the necessary accuracy down to tenths of a percent. Studying the damping of strings, he discovered that, in the presence of various vibrations of high and low frequencies, the high frequencies decay more slowly than they would if the process occurred only at high frequencies and the low frequencies were absent. A. I. Belov organized work on atmospheric acoustics, in particular expeditions to the polar regions to study the propagation of sounds in the stratosphere, and a number of other acoustic works.

A. I. Belov came from a hereditary working-class family; he was an excellent comrade and teacher, and an active public figure. A. I. Belov died in Leningrad, where he remained to carry on scientific work during the blockade.

The meeting stated that the development in the Soviet Union of work in acoustics and related disciplines, the growing importance of these works for various branches of the national economy, and the existence of a large body of material from already completed scientific works raise the question of creating a specialized journal.

The meeting noted the advisability of publishing books on the various branches of acoustics and of accelerating the publication of books now in print.

The meeting also resolved to carry out a broad and comprehensive study of the sounds of Russian speech and of the speech of other peoples of the USSR.

B. D. Tartakovsky