S. A. Rybak
N. N. Andreev Acoust. Inst. of Russian Academy of Sciences, Shvernik str. 4, 117036, Moscow, Russia
A very important social and economical problem arising before modern society is a struggle against the acoustic pollution of technological environment. At present, noise is one of the main emission factors in industry. At the same time, it should be noted that a tendency of production progress is such that further increase in noise emission should be expected. In practice, various methods for noise reduction at its propagation path are used: Reduction of the reflected energy fractions, proofing of a certain zone with a screen, etc. Both problems, acoustic designing of rooms in order to give them the desired properties and the noise reduction, require the data on acoustic characteristics of materials and constructions, and sound power of sound sources. Methods of determination of these characteristics are based on the measurements carried out in special rooms with specified acoustic properties---reverberation, ``dead'' and ``half-dead'' rooms. The special rooms of that kind are used for other purposes as well, for example, for generating the sound fields of high levels with special requirements to uniformity of frequency and spatial spectra, that is necessary when testing instrumentation and response constructions for acoustic strength. Successful solving of the problems mentioned above requires the development of an adequate model of the acoustic field in the closed space which is capable of describing the peculiarities of sound field generating in the rooms of various shapes and with various boundary properties. At present, several methods of representation of the sound field in rooms have been developed: An energy method, a method of acoustic mirages, and a wave theory. In practice, the most widely used method is the energy method which was offered at the beginning of the century and has been considerably modified in this report.