The physical phenomena occurring in sound-absorbing and insulating enclosures are subject of the present paper. These phenomena are: absorption in air and by the sound-absorbing material covering the walls and the coincidence effect. The absorption in the air can be neglected in small size enclosures for low ultrasonic frequencies (20-30 kHz). The coincidence plays a role in decrease of the sound insulation, however the main role play the leaks. The boards made of ceramic fibers have been chosen as the optimal sound-absorbing material. They are dense and have deeply porous structures. The enclosure for insulation of 20-kHz noise produced by a welding machine has been designed and manufactured, and reductions of 25 dB of peak and L eq levels have been achieved.

The phenomenon of the generation of acoustic waves in liquids based on interaction of alternating ion current and constant magnetic field is analyzed. The properties of such a magneto-electric transducer having no mechanical vibrating elements is examined theoretically (with the use of an electric equivalent circuit) and experimentally. The following measurements were carried out: (1) amplitude of conductivity current as a function of frequency, (2) amplitude of acoustic pressure at the distance of 0.5 m without constant magnetic field and (3) with magnetic field. For water from a municipal water-pipe network, the upper limit frequency of the current characteristic is 4 to 5 kHz. The same frequency properties exhibit a pressure characteristic. The directional pattern of the source depends on the shape of the electrodes and can be optimized for special aims. The energetic efficiency of the transducer is not great because the majority of the electric power is converted into heat and causes an increase in temperature of the liquid. That process is relative to a big value of resistance of weak electrolytes. That type of transducer can be applied in liquids without ion conductivity by submerging a container with very thin rubber walls and with mounted electrodes and filling with an electrolyte.

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Two methods of inclusion of coupling between the vibrating structure and produced acoustic field are discussed. The first iterative method consists of calculation of successive corrections of exciting nodal forces caused by sound pressure and solving the FEM equation of the structure. It has been proved that near the resonances of the structure this method can be nonconvergent. The second method consists of calculation of the generalized complex stiffness matrix of the sound field on the surface of the structure and including it into the stiffness matrix of the structure. The resulting stiffness matrix is a full matrix, and the algorithm for solving the FEM equation system is time consuming. It has been shown that near resonances of the structure, the global mechanical power provided to the radiating structure decreases in comparison to the power provided to the nonradiating structure. Near the antiresonant frequencies, the power provided to the structure with included radiation is greater. On this basis, a simple method of calculation of mechanoacoustical efficiency near the resonances and antiresonances of the structure is derived. The considerations are useful for calculation of efficiency of electroacoustical transducers. The results of calculation for vibrating and radiating shells of revolution are given.