In this report the tapered acoustic matching section was mainly analysed. On making appropriate assumptions, matching section may be considered as an inhomogeneous transmission line and its reflection factor can be calculated by solving the nonlinear differential equation of the inhomogeneous transmission line with a numerical solution, and the effect of a spacial part of the acoustic matching section can be analysed by utilizing the same, but by a simplified differential equation. By considering the frequency characteristic of acoustic matching sections, the author found the designing method of a broad-band acoustic matching section, by making the reflection factor sufficiently small with a choice of suitable length of a spacial part and an attenuation part at the lowest frequency.
Theoretical considerations have been performed for obtaining the energy density of the incident ultrasonic beam by measuring the acoustic radiation pressure on large objects in comparison to the wave-length of sound. Experiment has been performed by employing a balance-type radiometer and by employing spheres, cones of vertex angles of 60°, 90° and 120°, and plane discs made of different materials --- iron, brass, duralmin, bakelite and polystyrene --- as objects for measuring the radiation pressure. It has been observed that the spheres give constant and common values of the radiation pressure irrespective of the materials, and that they are satisfactory for absolute measurements. Iron and brass cones with vertex angle of 90° have given good results, too.
In an another report, under the assumption that the opening from a diffused sound field has the nature as though it is a plane-like assembly of non-directional point source, the author analysed the sound intensity attenuation along the perpendicular centre line from circular and slit-like opening of diffused room, and then proved experimentally that the logical formula of attenuation being applicable resonable for diffused sound of all frequencies. In this report, the author investigated sound directivities of sound radiation from the openings of diffused room, and sound transmission through them, experimentally and theoretically. From this investigation, the author illustrated that the sound directivity of sound radiation is non-directivity for low-frequency and for high frequency range, (ka≫1) the cosθ law is applicable, and that the sound transmission loss of the opening is zero for high frequency but for low frequency (ka<0. 5) the transmission loss of the openings cannot be neglected. Thus, the openings of diffused sound field show comparatively simple natures to free field and the application of its nature to architectural noise control is made with ease with wide application.
Theoretical formula is induced, in this paper, to express what effect is obtainable when the inner wall of a muffler is made absorptive. And an experiment is carried on to examine the theory induced here. The muffler with absorptive wall designed by one of the authors is shown in the last.