Broadband Low-Frequency Electroacoustic Absorbers Through Hybrid Sensor-/Shunt-Based Impedance Control

This paper proposes a hybrid impedance control architecture for an electroacoustic absorber, that combines an improved microphone-based feedforward control with a currentdriven electrodynamic loudspeaker system. Feedforward control architecture enables stable control to be achieved, and current driving method discards the effect of the voice coil inductance. A method is given for designing the transfer function to be implemented in the controller, according to a target specific acoustic impedance and mechanical parameters of the transducer. Numerical simulations present the expected acoustic performance, introducing global performance indicators such as the bandwidth of efficient absorption. Experimental assessments in a waveguide confirmed the accuracy of the model and the efficiency of the hybrid control technique for achieving broadband, stable lowfrequency electroacoustic absorbers. An application to damping of resonances in a duct is also presented, and the application to the modal equalization in actual listening rooms is finally discussed.