Mitigating the toilet flush noise: A psychometric analysis of noise assessment and design of labyrinthine acoustic Meta-absorber for noise mitigation.

Modern apartments in major cities are usually made of lightweight structures with inadequate acoustic properties, leading to a growing number of noise complaints by residents of inadequate sound insulation in high-rise buildings. When a toilet is flushed, loud and irregular sounds like humming, gurgling, or bubbling, "explosive" fury from vacuum-assisted toilets are generated. Though these toilet flushing sounds are not very harmful, they can still be perceived as nuisances by users nearby. The toilet flushing noise has posed a serious concern among apartment occupants and adjacent residents, causing health problems like sleep disturbance and irritation. In this study, the psychoacoustical investigations have been performed in four stages. In the first stage, the toilet flushing noise was recorded for several toilets with two designs: a close-coupled floor-mount toilet and a back-to-wall mount toilet. The second stage evaluated the physical and psychoacoustical characteristics of those recorded flushing sounds using psychoacoustic analysis software. The noise qualities were determined in the third stage by assessing autocorrelation function/interaural cross correlation function factors from the post-processed recorded sound data. Finally, we designed and successfully demonstrated an innovative acoustic meta-absorber prototype for mitigating the toilet flushing noise. The results have revealed a significant reduction in loudness because of meta-absorbers.