REFERENCE TRANSDUCER SELECTION FOR ACTIVE CONTROL OF STRUCTURE-BORNE ROAD NOISE IN AUTOMOBILE INTERIORS

A procedure for selecting the reference transducers for a feedforward active noise controller is presented. The method is applied to the pro blem of structure-borne road noise inside vehicles. Reference transduc er sets are selected based upon the maximum potential control of the i nterior sound field and the relative convergence rate. Maximum potenti al control and the relative convergence rate for a set of reference tr ansducers are shown to be independent. A method for predicting the sou nd pressure level reductions possible for a particular controller conf iguration was developed and verified, Predicted reductions were verifi ed experimentally by driving a tire of a test vehicle on a 1.7-m-diame ter roller. Measured values of reduction were found to be within appro ximately 1 dB of predictions, Using this prediction method, multiple r eference channels are shown to be beneficial only if a sufficient numb er of controller coefficients is used. Additionally, the prediction me thod was used to show that the incoherent output method of reference t ransducer selection will result in the largest possible control only i f a large number of controller coefficients are used. (C) 1996 Institu te of Noise Control Engineering.