Theoretical investigations are made on the sound radiation from a system consisting of a vibrating wall and a layer of porous material mounted on the wall. The wall has an arbitrary amplitude distribution and the material is in the same motion as the wall. The radiation field is obtained from the solution of a boundary value problem in the whole space including the inside of the material and free space in which the sound is radiated. The “generalized efficiency coefficient of radiation” is proposed. By using it, simple formulas for the radiation pattern and the radiation power are obtained.

View full abstract

The “synchronized correlation method” is a new correlation method which is useful for the field measurements of short-range sound propagation over a ground surface and for the impedance measurements of the surface. The advantage of the new method is that the coherency between transmitted and received signals can be recovered with the aid of a pilot signal and the measured cross-correlation function represents the impulse response of the acoustic system under test. Experiments are made over a turf-covered ground in two varieties of source-receiver arrangements. From the results in the vertical arrangement, the acoustic impedance of the ground surface is estimated. Experimental results in the horizontal arrangement are found to be in good agreement with the theoretical ones calculated from the estimated impedance. The effect of the irregularity of the ground surface is discussed.

View full abstract

Sound localization both in the horizontal and the median planes was simulated by the aid of a digital computer through two loudspeakers located in the traverse plane. The simulation was performed by the use of the measured head-related transfer function (HRTF) for two ears. Results of localization tests of three subjects with different sized pinnae show that:(1) When the subject's own HRTF was used in the simulation, natural sound localization in both planes can be performed with the same accuracy as real sound sources.(2) The differences between individual HRTFs affect the accuracy of localization in the simulation. In particular, in the median plane, an HRTF with a high angle-dependency seems to be more advantageous than one with a low angle-dependency.

View full abstract

A feedback theory on the organ pipe sounding mechanism was established for small amplitude oscillations. Lateral displacement of the jet at the edge is amplified to produce the driving current, part of which is fed back to the jet. The self-sustained oscillation is realized if amplification and feedback functions combine to unity in the feedback loop. Numerical calculation clarified that (1) phase shift due to the lip-to-edge transit time of the jet has physical significance, and its range for sound production extends roughly between π/2 and 3π/2, (2) feedback oscillation must be maintained by the decrease of phase shift with ascending frequency, (3) “octave jump” occurs and the phase shift is doubled for such high speeds as exceed the allowable limit, and (4) oscillations take place at the antiresonance of the current-driven parallel system. Experimental results on four models made by authors encourage our feedback excitation theory.

View full abstract

New equations are proposed for stress measurements in orthotropic materials by ultrasonic birefringence technique. Intensity of stress-induced anisotropy and its principal direction are related to the applied stress through three coefficients, in contrast to only one coefficient required for isotropic materials. Experiments of ultrasonic birefringence were carried out to determine the three coefficients in a plate of aluminum alloy with a slight orthotropy originated from roll working. Anisotropy induced by uniaxial stress and rotation of the principal axis were observed in several specimens with different directions of rolling. The results are in good agreement with the curves theoretically predicted by the equations proposed here, showing the validity and usefulness of these equations for stress measurements in materials conventionally used.

View full abstract

A simple mechanical low-pass filter was applied to a vibration isolator for portable vibrating tools for the purpose of establishment of its design method. As the isolator was inserted between the tool and the human hand, the effect of terminating the isolator by the human hand on transmission of the vibration was studied on the isolator with and without a mechanical resistance. For analysis of the total system, the theory of electric transmission circuits was used after conversion of mechanical systems into equivalent electric circuits by employing the force-current correspondence. The mechanical impedance was utilized for the simulation of the human hand. A possibility of substitution of the hand for the equivalent pure mass was confirmed in the low frequency region.

View full abstract