Abstract
There is a demand for the expansion of appropriate systems to control engine noise inside a vehicle, so that the interior levels do not rise when the vehicle weight is reduced. One technique with tremendous power for low frequency noise reduction is Active Noise Control (ANC). In this work, an ANC system has been developed to reduce the booming of a prototype van arisen when the engine noise excites some modes of the passenger compartment. Specially, the 80-250 Hz frequency range is of primary interest. This work deals with the design and the physical implementation of a multichannel feedforward ANC system using microphones as error sensors and loudspeakers as secondary sources. First, a reference signal coherent with the unwanted noise has to be searched. The error microphones have to be positioned to avoid the nodes inside the compartment. The optimal locations of loudspeakers are found by simulated annealing, taking into account that the acoustic field inside the van is expressed as the sum of a series of acoustics modes, and the secondary sources must be positioned so that they can couple with these modes and reduce the sound pressure levels in the interior of the cabin. A six-inputs-six outputs control system is implemented by means of a commercial ANC system. Measurements of noise reduction has been carried out in the semianechoic room at NECT-E under usual driving conditions (3rd gear, fast acceleration).