Helmholtz Resonator with Sonic Black Hole Neck

Abstract

The acoustic performance of a Helmholtz resonator (HR) with a sonic black hole (SBH) neck is investigated in this study both theoretically and experimentally. The proposed SBH neck for a HR consists of a cylindrical tube with a set of rigid thin rings. When the inner radius of the ring is linearly decaying, the SBH effect can be obtained. The sound absorption performance of the proposed HR is then derived based on the transfer matrix method (TMM). Finally, the proposed HRs under different sizes are fabricated by a 3D printing apparatus. The analytical acoustic absorption results are compared to the experimental data obtained from an impedance tube setup. The absorption coefficients from TMM and experiments show a reasonable agreement. When compared to the traditional HR, he main advantage of the proposed HR with a SBH neck is that the broadband sound absorption in a non-HR-resonance frequency range can be achieved.