Internal ported band pass enclosure for sound cancellation

Abstract

A transducer arrangement for active noise cancellation in conduits, for example, in motor vehicles where an electronic control produces a drive signal for a transducer that emits cancellation pulses phased 180.degree. from the sound pressure pulses passing through an exhaust conduit, where both front and rear sides of the transducer are acoustically coupled to improve the efficiency of the transducer operation. Preferably, the acoustic coupling comprises an enclosed chamber partitioned to expose a first transducer side to a chamber portion and a second transducer side to a second chamber portion. A first port couples one of the chambers to the other and a second port couples one of the chambers to the conduit. Each port for communicating with the conduit can be tuned to resonate at predetermined frequencies. When both sides of the transducer are so coupled to the conduit, the transducer has increased efficiency over a band of frequencies, to accommodate the frequencies generated by a source of noise while limiting access of fluid or heat in the conduit to the transducer. A tandem transducer mounting arrangement according to the present invention reduces vibration of the housing. The system is particularly suitable for use in adapting noise cancellation techniques to replace or combine with passive mufflers on motor vehicles.