Striking force, between a piano hammer and a string, was measured on a time axis. Furthermore, simultaneously measured was the displacements of the piano string and hammer-wood to obtain the compression-displacement of hammer felt from the difference between them. The compression-displacement of the felt is larger, at the time when the hammer is finally detached from the string, than the half of the compression-displacement maximal in a striking interval. The temporal variation of the virtual stiffness was obtained numerically from the compression-displacement and the striking force to result in the variation similar to that of the striking force. Because of this experimental result, assumptions on the stiffness in a striking interval, such that the stiffness is fixed or proportional to the square root of the displacement, do not reflect the reality.
Survey on environments of 315 residences in Nagoya city including reactions of inhabitants to noises was made in the last half period of 1982. By using these data disturbance of sleep by noises is analyzed in this article. The following results are obtained. 1) Percentage of disturbed people is about 30% which is consistent with the results reported on other cities. 2) The main noises for disturbance of sleep are unusual sounds relevant to road traffic and neighbor activities. 3) Influences of noise environment around residence, land use, type of house, age of inhabitant, season and other factors on sleep disturbance in daily life are perceived, but none of them are prominent.
Experimental data for propagation and beam pattern of parametric pulses have been presented in this paper. Two pulses are generated by finite amplitude acoustic wave with rectangular envelope. As sound source level increases, primary and harmonic components are saturated, however, parametric pulse is not saturated. Experimental results are explained by the theory developed by Merklinger [J. Acoust. Soc. Am. 58, 784-787 (1975)]. A new type of signal transmission using the conception of the digital communication has been proposed. Namely, the parametric pulse train that has the modulated amplitude with desired signal are generated by the primary wave with sawtooth envelope. It has been showed that this method is able to overcome ground noise and reduce the load of the sound source.
In ultrasonic plastic welding, as is well-known, tools with about a half wavelength width or more and with proper slits are widely used for bonding wide plastic works. The vibrating surfaces of such tools vibrate uniformly like pistons. However the vibration mechanism has not been made clear yet. To make clear the vibration mechanism of the tool with slits, the radiation surfaces of the tools are kept in contact with the surface of the water and ultrasonic radiation patterns in the water, especially transient radiation patterns, are observed by a stroboscopic schlieren optics, where the tools are excited by periodical burst waves. It is proved by the observations that the tool with proper slits is a unity of the longitudinal unit vibrators with the same resonance frequency and that the shear forces between each unit vibrator make the radiation surface behave like a piston.