Longitudinal and torsional vibrations of helical springs of finite length with small pitch are analyzed on the basis of Love's formulation of the naturally curved thin rods of small deformation. Driving-point impedance at one end of the spring is discussed in two cases where the other end is free and supported respectively. Image impedance and propagation constant are also taken into account to describe the transmission characteristics by analogy to electrical four-terminal network.
Noise from diesel pile hammer during piling work was measured under two different conditions. One is an specified experimental condition under which the hammer drives a steel pipe pile remaining at a constant length in the test field of operation and other is actual one under which the hammer drives the pile actually in construction field of various sites. Sound levels (A) and (C) were measured at a distance of 10m from the piling position by a sound level meter, and number of blows per minute were counted. Sound level measured under both conditions was given as a function of the energy output of the hammer, and the following empirical formula was obtained. Sound level (A)=83+5log_10 2WH dB (A) W: ram weight (kg) H: ram stroke (m)
As a basic study on sound reflectivity of a panel array "clouds" in auditoria, the sound reflectivity of a rigid rectangular panel was calculated by the Fresnel-Kirchhoff's diffraction formula given by the Kirchhoff's boundary conditions, and compared with the measured values by the pulsed-tone method. Under the adequate restrictions, the approximate formula based on the Fraunhofer diffraction is more useful than that based on the Fresnel diffraction. The sound reflection from a panel of irregular shape was estimated by dividing it into rectangles and then summing their effects. A reflection-diffusion function is defined for an absorbing panel. For a reflecting uniform specularly panel, this function agrees with the reflection coeffcient as determined by the "Interference Method". The sound reflection from an array of square panels is calculated by summing the effect of each. Good agreement between theory and experiment has been found over a wide range of reflection angle and frequencies, except in the lower frequencies.
Floating floor mats for improving impact sound insulation are in general used under loading conditions. This article describes the aging effect of some materials on impact sound insulation together with a change of the dynamic elastic modulus of the materials with time.
In most acoustic instrument design in the past, attempts were made to obtain flat frequency response using the equivalent relationship of electro-mechano-acoustical systems. But nowadays, this method has been completed and it seems diffcult to improve the behavior of the instrument remarkably by this technique. In view of this, development of a new design method is being looked forward to. The application of the Multi-Resonance System is considered to be one of the feasible technique for this purpose. To utilize such technique, it is necessary to develop an effective means for controlling the fluctuations of frequency response. In this paper, a method of control by adjustment of damping resistance value is discussed by using some equivalent circuits. There are two kinds of damping resistance ; branch resistance and common resistance. As the branch resistances become larger, the peak levels decrease monotonically but the dip level initially increases to a maximum value and then drops. The average level decreases to about -3dB when the peak and dip levels coincide. However, when the common resistance becomes larger, the peak level decreases but there is no change in the dip level.