Studies have been carried out to improve the sound insulation in the audible frequency range using sonic crystal(SC) in a multi-panel structure. And studies have also been carried out to improve the sound insulation by applying local resonant SC to a multi-panel structure. Analytical and numerical studies of improving the sound insulation using SC have mostly considered only the cases where plane waves are incident perpendicular to the sound insulation structure. And they also evaluated infinite scatterer arrays using periodic boundary conditions for the reduction of computational load.
We comprehensively investigated how the sound insulation of a finite double-panel structure(DPS) with periodic arrangement of cylindrical shells varies with the angle of incidence of sound waves. The variation of the sound insulation with the incident direction was considered in relation to the acoustic modes in the finite air region. By using a certain thickness of sound absorbing material, the longitudinal acoustic mode is attenuated, while increasing the sound insulation, the change of the sound insulation with the incident angle is reduced. We also evaluated the change of the sound insulation around the frequency where constructive and destructive interference occur with varying shell thickness. The presence of a porous material thickness above a certain value (30 mm in our case) can sufficiently eliminate the parallel acoustic modes, thus improving the sound insulation in the frequency range around them by more than 10 dB and minimizing the change in the incident angle of the sound waves. The characteristics of the change in sound transmission loss(STL) with varying shell thickness were evaluated, and the sound insulation around the frequency at which constructive interference occurs (1600 Hz to 3700 Hz in our case) when the shell thickness is thinner can be improved by more than 10 dB.
The result has been published in the "ARCHIVES OF ACOUSTICS"(Vol.48, No.3, pp.381-388(2023)) under the title of "Relationship between the sound transmission through the finite double-panel structure with a cylindrical shell array and the vibro-acoustic characteristics of its constituents"(https://doi.org/10.24425/aoa.2023.145244).
