FEASIBILITY STUDY OF A VIBRATION CONTROL ACTIVE EAR DEFENDER

Traditional active ear defenders make use of an error microphone and a loudspeaker as the actuator to reduce low frequency noise at the ear. The loudspeaker is sometimes used for communication as well. In cases when communication is not needed it may be possible to do without a loudspeaker-microphone pair and use a vibration actuator to directly excite the ear-cup itself and a vibration error sensor. This paper presents the results obtained in developing such a device. A theoretical model of the system is first derived and simulation carried out to show the effectiveness of the novel active ear defender for the case of feedback control. An experiment with an actuator attached to the ear-cup and an accelerometer as the error sensor is also presented to show the feasibility of the system. Results indicate that one main advantage is that the vibration open-loop frequency response varies little with changes in the acoustical properties of the active ear defender compared to the traditional one. Hence robust closed-loop stability independent of the wearer can be anticipated. Some of the limitations are also discussed in view of future practical applications.