Norihisa Hashimoto

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.

Experimental study on sound insulation of membranes with small weights for application to membrane structures

Abstract In an earlier paper, it was shown that attaching small weights to a membrane (called MAW) improves the sound insulation in the low-frequency range. By applying this particular membrane to membrane structures, the sound insulation is improved without decreasing the light-transmission efficiency of the membrane. Experiments on the sound insulation were carried out to confirm this capability, and the results are as follows. 1. (1) Sound-insulation mechanism of MA W has been identified in a diffuse sound field. 2. (2) A double-layer membrane consisting of MAW and an ordinary membrane indicates 5–11 dB greater transmission loss in the low-frequency range than the double-layer membrane which is composed of two ordinary membranes. 3. (3) The effect of MAW disappears when the thickness of an air layer is less than 100 mm. A thickness of over 500 mm has to be kept maintained in order to get the special effect.