Broadband Sound-Absorbing Tile Comprising Nonwoven Sheet with Back Air Space and Helmholtz Resonator

A broadband sound-absorbing structure that combines a nonwoven sheet with a back air space and a Helmholtz resonator is proposed. The incident surface of the nonwoven sheet with the back air space is divided into two areas, and a sound-absorbing tile with high sound absorption coefficients across a wide frequency range is created by incorporating a Helmholtz resonator at the end of one of the back air spaces. Theoretical and experimental analyses were performed. Sound absorption coefficients were measured using a two-microphone impedance measurement tube and the theoretical values were derived using the transfer matrix method. The results demonstrate that the proposed sound-absorbing structure exhibits high sound absorption coefficients across a wide frequency range for both experimental and theoretical values. The sound absorption coefficient of the proposed sound-absorbing tile is improved in the low-frequency range, and the dip in the high-frequency range is eliminated. The sound absorption curve of the proposed tile became broader compared with either the Helmholtz resonator alone or the nonwoven sheet with a back air space alone. Theoretical values closely match experimental trends; thus, it is possible to estimate the sound absorption coefficients of the proposed structure with sufficient accuracy for practical applications.