Research on self-sensing impedance control method for adjustable low-frequency sound absorption

Conventional passive sound absorbers are limited in low-frequency performance due to the constraints of long wavelengths and structural dimensions. This paper proposes a self-sensing acoustic impedance control method that achieves broadband low-frequency absorption without relying on external sensors. The method utilizes the electromechanical coupling of a loudspeaker for both sensing and actuation, while a finite impulse response filter (FIR) is adopted as the control algorithm, offering greater flexibility compared with shunt loudspeaker designs. A lumped-parameter model is first established to analyze the interaction between the controller and the diaphragm surface, from which the equivalent acoustic impedance is derived as a function of the FIR filter coefficients. Theoretical analysis shows that the first-order characteristics of the FIR filter modify the effective mass and damping of the diaphragm, shifting the absorption peak, whereas the higher-order characteristics suppress the acoustic reactance, enabling broadband absorption in the low-frequency range. Numerical simulation is employed to analyze the tunable acoustic performance of the device. Experimental validation in an impedance tube verifies the effectiveness of the proposed method. With different parameter settings, the absorber achieves absorption coefficients above 0.6 in the 150-300 Hz range, and it is consistent with the analysis results.