Design of active Multiple-degrees-of-freedom electroacoustic resonators for use as broadband sound absorbers

We present a novel control method achieving stable multiple-degrees-of-freedom electroacoustic resonators. Such broadband absorbers, composed of a feedback-controlled electrodynamic loudspeaker, have many practical applications to real-world acoustic engineering problems, such as low-frequency industrial noise reduction in the range of [20 - 200 Hz]. The proposed control architecture combines a conventional microphone-based feedback control loop and a current-driven direct acoustic impedance control scheme, proven to perform optimally in recently reported acoustic impedance synthesis methods. This paper presents a methodology for designing the transfer function to be implemented in the controller, after specifying a target multiple-degree-of-freedom acoustic resonator impedance. Numerical simulations presents the expected acoustic performances, confirmed by experimental assessments in an impedance tube.