This letter proposed advantageous in-uniform gradient cross-section (GCS) channels which weaken the dependence of the coiled-up anechoic metasurface on the total channel length. The privilege of GCS channels was revealed by studying Fabry-Pérot absorbers with designed channel widths. A theoretical framework was set up to explain the inherent sound absorbing mechanism, from which the overall performance as well as dominant working frequencies of linear and exponential GCS channels can be predicted. With proper GCS channel design, the proposed structures were experimentally and theoretically proven to achieve lower absorption frequencies in comparison with conventional uniform cross-section absorbers with the same exterior geometry. Through a parametric study on the near-perfect absorption frequency range of GCS absorbers, the strong tunability brought by GCS was confirmed, suggesting the possibility of on-demand frequency-oriented absorber design. Serving as an approach for acoustic impedance transferring, promising features of GCS can be extensively applied in existing coiled-up anechoic metasurfaces.
This letter explores a least absolute shrinkage and selection operator- (Lasso-) based beamforming algorithm for a sparse cylindrically baffled speaker array, which can be used for low-cost multi-channel surround sound reproduction. The proposed method exploits the inherent sparsity of the Lasso algorithm, and achieves both narrower beamwidth and a smaller side lobe in comparison with existing algorithms in both simulation and experiment. In addition, further study on the dependency of operating speaker sparsity on regularization parameter enables user preference-based adjustment in practice.
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