Hidemaro Shimoda

Generation and the measures of impact sound by stick‐slip phenomenon at beam joint in buildings (the first report)

It is often happened to be annoyed by the sound of an uncertain cause in the completed buildings. The phenomenon might be repeated indefinitely though most of these sounds are canceled with the passage of time. This paper reports a series of processes from the investigation of the cause, to effective measures on the case in a high rise housing complex. And the ascertained cause is thought to give a systematic explanation to this kind of uncertain sound in buildings. The outline of this paper is as follows. (1) It paid attention to the vibration wave form (phase) to which it propagated in the building frame to specify the position in the plane of the slab, the vibration accelerometers were arranged in two dimensional distribution on the slab, and the source was ascertained adequately. (2) It was clearly specified that the cause of generation was ‘‘stick‐slip phenomenon’’ in the beam joint part from the wave form of the generated sound and its spectrum of the vibration. (3) Appropriate measures construction...

New approach of the model experiment in room acoustics—advantage of 1/16 scale model

In the construction of the auditoria, the examination by the acoustic model experiment has been often performed. This paper describes the outline of the result of investigating various features of the method of the experiment by 1/16 scale models compared with models of 1/10 and 1/20 scales that have been generally adopted up to now. That is, the following advantages are found in the case study of the 1/16 scale model experiment, and the new approach to the model experiment method is proposed here. (1) full cover of the band to 4 kHz enables the quantification of a practical physical acoustic parameters. (2) The parameter as the air absorption coefficient in the supersonic wave band by 1/10 scale models can be used. (3) Cheap digital sound recording system can be used considering the microphone characteristics. (4) The model construction cost can be largely saved compared with 1/10 models.

An echoic room model for acoustic simulations by non‐reflection boundaries using the Bergeron method

An analytical model of anechoic rooms by distributed equivalent circuits is constructed in the computer using the Bergeron method [Shimoda et al., ‘‘Analysis of sound fields in rooms using Bergeron’s method,’’ Trans. I.E.C.E. Japan, 72 A, 1, 1–11 (1989); English transl., 1989 Electronics and Communications in Japan, Part 3, Vol. 72(12), Scripta Technica, Inc. (Wiley, New York, 1990)]. In this analytical method, the nonreflection boundaries are modeled by gradually increasing sound transmission losses in specific regions near boundaries just like a sand beach exposing sea waves. Also, the sound transmission characteristics or the sound pressure distributions in the room are investigated. The model can be applied to the sound scattering analysis by an arbitrary object.

A study of an impedance reflection model of sound fields in rooms using the Bergeron method

In the Bergeron method [Shimoda et al., Trans. Inst. Electron. Commun. Eng. Jpn., Part A 72, 1–11 (1989); English transl., 1989 Electron. Commun. Jpn., Vol. 72; Scripta Technica, Inc. (Wiley, New York, 1990)], sound reflection surfaces in rooms are modeled by the simple resistances corresponding to the rigid walls. And the low‐frequency responses for a middle scale of auditorium are agreed preferably with the real fields [K. Nakagawa and H. Shimoda, ASVA 97]. However, for big absorption acoustic models such as recording studios, or mixing rooms, the surfaces in rooms must be modeled by the impedance reflections. In this paper, the basic treatments for the impedance reflection models in the Bergeron method are investigated, and the wideband time‐stretched pulses are used to simulate one‐dimensional sound fields. The feasibility of numerical simulations using the Bergeron method are confirmed by supposing a simple surface impedance reflection model.

Characteristics for vibration damping of the concrete included secondary subject

A concrete structural material with damping performance for vibration has been investigated. It is proposed that in order to reduce the sound propagation in the solid material, the concrete material disperses many small cells in which many easy moving particles are included. It is expected that the vibration energy which is applied to the material is absorbed by the impaction and friction of the particles alternatively and between particles and cell’s wall. The preliminary experiment to confirm the capability of the high damping material on the basis of this concept has been carried out. It was shown that damping performance of the specimen depended on the size, the density, and the volume fraction of the particles by the impact vibration testing for the coupon‐sized test specimen. The effect of the easy moving particles for reduction of the sound propagation in the solid was confirmed by the sound propagation testing for the middle‐sized panel specimen.

Time response analysis of sound fields in rooms and the temperature condition of the air

Transient analysis in the time domain is very important to determine acoustical properties in rooms. In this paper, the transmission line network is used as a simulation code named Bergeron’s method [J. Acoust. Soc. Am. Suppl. 1 84, S64 (1988)]. Time responses in the rectangular scale model excited with pure tones were compared to analytical results. In the study, the medium condition as a temperature of the air turned out to be very sensitive to simulated time responses in sound fields in rooms. Even though it is known that the sound speed varies with a change in the temperature of the air, the standard sound speed corresponding to the standard temperature of the air, such as 15 °C in ordinary sound field simulations, is often used. Analytical time responses, however, as compared with experimental responses in the model, were found to be very different from each other in about 1% change of the sound speed.

Verification of Bergeron's analytical method applied to room acoustics

Applicability of the Bergerons method to room acoustics has been studied, and was found useful for a transient analysis in the time domain [J. Acoust. Soc. Am. Suppl. 1 84, S64 (1988)]. In this paper, a verification study of the proposed analytical method is presented. Transient time responses and reverberation times measured in a rectangular scale model were compared to the analytical results. The time responses at six positions in the room were observed by pulse excitation with 1/3‐octave‐band tone burst, and reverberation times were evaluated from these responses using Schroeders integrated impulse method. Each time response at various points agreed very well with that of the scale‐model experiment and the average of calculated reveberation times also agreed favorably with the experiment.

Analysis of sound fields in rooms by Bergeron's method

The behavior of sound wave motion in rooms is so complicated that it is not easy to treat it theoretically unless simple geometrical shapes or simple boundary conditions are assumed. This study presents a formulation applying Bergerons method, developed for an electromagnetic field simulation by computer [N. Yoshida et al., Trans. IECE Japan, J62‐B, 6, 511–518 (1979)], to room acoustics. In this formulation, the sound field is represented by an electrical equivalent circuit composed of distributed lines corresponding to the acoustic equation, and nodal equations for each connection of the lines are derived. As an example, consider a cube‐shaped room with uniform absorption by each wall. The transient responses to the sinusoidal waves and the 1/3‐octave‐band tone burst are calculated, and the stationary sound‐pressure distribution and the reverberation time are obtained from these responses. The results show the validity of the formulation and prove the effectiveness of the application of this method to r...