In recent years, the growing demand for airtightness of residences has caused several problems with indoor humidity management, e.g., mold growth and dew condensation. Therefore, in order to maintain humidity at a comfortable level, charcoal chips with moisture absorption and emission properties are spread into air cavities above suspended ceilings and below floor systems. The charcoal chips may affect the acoustic performance, e.g., floor impact sound insulation, because they are porous and add a load weight to the ceiling system. Therefore, we measured the impact sound pressure level in residences and laboratories under three different conditions: without ceiling, with ceiling, and with charcoal chips applied to ceiling boards. In these cases, the floor impact sound with the charcoal chips was reduced by approximately 2 and 5 dB at 63 and 125 Hz, respectively, as compared to without ceiling. Thereupon, we investigated the vibration characteristics of the ceiling boards and the reverberation time in receiving rooms to analyze the generating mechanism of the floor impact sound. Consequently, we found that the main factors in reducing the floor impact sound were damping and reduction of vibration of the ceiling boards with charcoal chips.
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