Multiple-Tone Sound Absorber Based on a Multiple-Branch Shunted Loudspeaker

Conventional passive sound absorbers are usually tried to achieve broadband sound absorption. However, low-frequency noise in aircraft cabins often contains pronounced discrete-frequency components. In this situation, a broadband sound absorber may not be necessary, only a tunable sound absorber at desired discrete frequencies is needed. To address this issue, this study proposes a tunable multiple-tone sound absorber based on a multi-branch shunted loudspeaker (MBSL), in which a single loudspeaker is connected to multiple parallel inductor-capacitor-resistor (LCR) shunt circuits. An electromechanical-acoustic coupling model is established, and the sound absorption coefficient for proposed absorber can be obtained. A two-stage parameter-design method is then developed. Analytical initial branch parameters are first obtained through local admittance matching, then a local coupling coefficient is introduced to evaluate the contribution of the non-target branches. Residual-admittance compensation is subsequently applied to refine the initial parameters and improve the total-admittance matching accuracy. Numerical results demonstrate that multiple absorption peaks can be obtained at targeted frequencies. Furthermore, it is found that the resistance at each shunt branch mainly regulates the absorption-peak amplitude, whereas the branch inductance primarily controls the peak frequency. Impedance-tube and one-dimensional duct experiments further confirm the local branch-regulation characteristics and the effectiveness of the proposed system. The results demonstrate that the MBSL enables tunable multiple-tone sound absorption using only a single electroacoustic unit and provides a compact solution with an explicit analytical design procedure.