Cause and perception of amplitude modulation of heavy-weight impact sounds in concrete wall structures

• Two closely spaced modes existed for vibrating floor in concrete wall constructions.
• Side wall rigidity determined difference of natural frequencies of the two modes.
• Simultaneous excitations of the two modes generated low-frequency modulated sounds.
• The impact sounds were judged to be 3–5 dB more annoying when modulated.

This study investigated amplitude-modulation effects on the heavy-weight floor impact sound caused by a vibration of concrete wall construction. The fundamental resonance of a floor in concrete wall construction consists of two closely spaced vibration modes. These modes were identified from experimental modal analysis of an actual multi-story building. The modes corresponded to in-phase and out-of-phase vibrations of the upper and lower floors. The rigidity of the side walls had influence on the difference between the natural frequencies of the two modes. Low-frequency modulated sounds were generated in a room by the simultaneous excitations of the two vibration modes. The heavy-weight impact sounds were analyzed using auditory experiments to determine the amplitude-modulation effects on the perceived annoyance. The highly modulated impact sounds were judged to be 3–5 dB more annoying than the one having the same level without modulation. Consequently, impact sound transmission from floors connected by less rigid side walls exhibited lower annoyance.