Abstract-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.

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In this paper, we theoretically, numerically and experimentally demonstrate the acoustic isolator effect in a 1D waveguide with direction dependent controlled boundary conditions. A theoretical model is used to explain the principle of non reciprocal propagation in boundary controlled waveguides. Numerical simulations are carried out on a reduced model to show the non-reciprocity as well as the passivity of the system, through the computation of the scattering matrix and the power delivered by the system. Finally, an experimental implementation validate the potential of programmable boundary conditions for non reciprocal propagation.

We introduce an active concept for achieving acoustic metasurfaces with steerable reflection properties, effective over a wide frequency band. The proposed active acoustic metasurface consists of a surface array of subwavelength loudspeaker diaphragms, each with programmable individual active acoustic impedances allowing for local control over the different reflection phases over the metasurface. The active control framework used for controlling the reflection phase over the metasurface is derived from the Active Electroacoustic Resonator concept. Each unit-cell simply consists of a current-driven electrodynamic loudspeaker in a closed box, whose acoustic impedance at the diaphragm is judiciously adjusted by connecting an active electrical control circuit. The control is known to achieve a wide variety of acoustic impedances on a single loudspeaker diaphragm used as an acoustic resonator, with the possibility to shift its resonance frequency by more than one octave. This paper presents a methodology for designing such active metasurface elements. An experimental validation of the achieved individual reflection coefficients is presented, and full wave simulations present a few examples of achievable reflection properties, with a focus on the bandwidth of operation of the proposed control concept.