Masahito Yasuoka

Sound insulation of a rectangular thin membrane with additional weights

Abstract As a result of experiments on sound insulation under conditions of normal incidence, it has been confirmed that attaching small weights to a membrane improves the sound insulation efficiency in a frequency range from natural frequency of the whole membrane to that of the partial area divided by the additional weights. This effect is due to the interfering mode mixing of the fundamental normal mode of the membrane and the divided mode with the same phases formed by attaching the additional weights to the membrane, and not due to mass law. In the present paper this mechanism is studied and revealed through both experiments and numerical analyses. This method is simple, lightweight, possible to tune and effective in a lower frequency range, and hence it is thought that this method has the possibility of being developed into a useful one in the field of noise control.

Blind source separation and sound source localization on time‐frequency domain considering time lag information

The blind source separation and sound source localization based on independent component analysis on time‐frequency domain considering time lag information between source signals and observation signals are conducted. The formulation based on the independency of time‐frequency domain and the linearity of source signal is presented. The method which can be conducted not only the separation of source signals but also the specification of location of source signals is proposed through the consideration of time lags. Using this method, it can be analyzed even if observation signals include an intermittent noise, under the assumption of some independency of source signals. First of all, the number of source signals is specified through the quotient of complex valued time‐frequency information of two observation signals. Next, the locations of source signals are specified using the relationship of relative time lags between source signal and observation signal. Then, the source signals are obtained by use of th...

Study for blind source separation on time‐frequency domain considering phase information

The methods that can be done for the estimation of the number of source signals and separation of source signals using time‐frequency information are proposed as a method of blind source separation. In these methods, some independent conditions are assumed in a time‐frequency domain, and observed signals are expanded to time‐frequency domain using wavelet analysis. However, these methods are not considered phase differences (difference of distance) between source signals and observed signals. A new method is proposed. The method can be done not only for the source separation but also the specification of the locations of source signals considering phase differences. In this method, it is necessary to assume a rather stronger independent condition than former methods. But, on account of this assumption, a function that becomes a real value only when phase differences are coincidence in time‐frequency domain is determined. Using this function, first of all, the number of source signals is calculated, then t...

An approach utilizing membrane materials to regulate modal characteristics of rooms

Abstract A passive approach, using membrane materials for regulating modal characteristics of rooms, is presented which improves undesirable acoustic properties in rooms at low frequencies without modifying room shape. Basic studies are conducted to examine the possibility of this approach through scale model experiment and computational analysis, where the effect on the modal distribution and the sound energy distribution in a rectangular room are investigated. The results show that the modal distribution is remarkably transformed depending on the surface density and the position of membranes. Moreover, they demonstrate some cases where high uniformity in the modal distribution and reduction in the spatial deviation of sound energy are achieved by using membranes even in the room originally having low uniformity. These findings indicate that the present approach works effectively under the proper installation of membranes, and, on the other hand, it requires the prediction of the effect in advance.

Loss factor at the boundary of a single‐leaf wall under a vibrational field of diffused bending waves

The internal loss factor (etaint) is an important parameter in the case of calculating the transmission loss of a panel by using SEA (statistical energy analysis). Though energy loss at the edge is fairly large in practical walls, etaint have been ordinarily treated including the edge loss. So it must be necessary to treat quantitatively the energy loss at the boundary of the wall. In this paper, assuming that a panel in excitation is a two‐dimensional vibration field of diffused bending waves, a formula of the decay time of a panel is deduced. The subject for experimental study is an aluminum panel mounted in the opening between transmission suite. The panel is excited by a piezoelectric ceramic diaphragm. Vibrational decay time is measured by the impulse response method. The calculation method of the energy absorption coefficient and loss factor at perimeter is indicated by using measured values of decay time and sound radiation.

Review of research reports on floor impact sound in Japan

The authors have reviewed technical papers on floor impact sound reported in journals and proceedings published by the Architectual Institute of Japan, the Acoutical Society of Japan, and the Institute of Noise Control Engineering Japan. Research on this subject started in the 1960s in Japan, with considerable delay from the development in this area in North America and Europe. However, in the last decade, approximately 25 papers have appeared on this subject every year, and the total number of the relevant papers in Japan has been found to exceed 400. The number of research works on floor impact sound in Japan is characterized by the use of a soft and heavy impact source (a tire for compact cars). As is widely known, this source is the standard impact source unique to Japan. However, approximately half the recently reported papers deal with noise produced by the tapping machine. This change seems to reflect the Japanese consumers’ general choice of floor lining changing from carpets to wooden floor cover...