Electroacoustic Absorber Using Disturbance-Observer-Type Velocity Estimator

An electroacoustic absorber (EA) using the direct impedance control (DIC) technique for broadband noise reduction requires a pair of pressure and velocity sensors. Due in part to the need for an array-type EA for acoustically large spaces, its installation cost increases. To overcome this problem, an EA using a disturbance-observer-type velocity estimator instead of a velocity sensor is proposed in this paper. To verify the feasibility of the proposed EA system, its specific acoustic admittance and noise absorbing performance are investigated and compared with those of an EA using a velocity sensor. The experimental results show that the proposed EA system performs sufficiently well for the frequency range of interest (20-500 Hz). Since the frequency range of interest may differ depending on the users' needs, it is more effective to adjust the noise absorbing performance of the EA. Therefore, it is also suggested to modify the original Q-filter by adding a lag compensator in the disturbance-observer-type velocity estimator. The stability issues of the proposed EA systems are addressed. The proposed EA system with the modified Q-filter can be expanded to an array system for practical acoustic noise control problems such as room acoustic modal control and vehicle interior noise control.