Numerical analyses and experimental evaluation of reduction technique for sound transmission through gaps

Unintended gaps that occur around door sets and windows cause sound leakage and decrease sound insulation performance. In the Boundary Element Method (BEM) analysis, sound transmitted through a gap is expressed as the integral of the particle velocity. This means that the transmitted sound field can be expressed based on the particle velocity at the gap only. Hence, it is demonstrated here through numerical analysis that a decrease in sound insulation performance is caused by an increase in sound particle velocities in the vicinity of gaps in a rigid wall. We call this phenomenon the “gap effect”. It is also shown that the movement of particles around the gaps can be suppressed by installing a thin sound-absorbing material such as thin or nonwoven fabric, reducing the sound leakage from the gaps. Furthermore, the sound insulation performance obtained by suppressing the particle velocities at the gaps is experimentally verified. The results of this study show that the improvement observed in the sound insulation performance following the installation of sound-absorbing layers into the gaps is quite significant and is suitable for practical use.