Effect of structural vibration and room acoustic modes on low frequency impact noise in apartment house with floating floor

In today's apartment houses, adoption of floating floor has vastly improved structure-borne floor impact noise by isolating vibration components well in excess of the major structural vibration resonant frequencies. For 20-200 Hz frequency region encompassing major structural vibratory and room acoustic modes, however, impact noise attenuation is much harder to achieve, and the problem can be exacerbated for small rooms where these modes are sparsely placed in audible frequency range. Experimental and numerical investigation of the effect of structural vibration and room acoustics on impact noise for the frequency region is undertaken. Structural vibration modes of the room with floating floor correlate well with the spectral characteristics of the impact noise, with various structural parts making different contributions in the frequency domain. For the low end of the impact noise spectrum, low density of high-energy axial room acoustic modes arising from small room size causes sound field in the room to show notable variation with measurement locations. For the mock-up typical of a small-sized living room considered in the present study, one of the vibrational mode of floor slab excites an overlapping fundamental room acoustic mode that further amplifies the impact noise. A room design that avoids overlapping of major structural and acoustic resonance modes at low end of the audible spectrum could be crucial in abating an echo commonly encountered in bare apartment rooms.