A Study On Error Microphone Location For Active Sound Radiation Control

The physical configuration of an Active noise control(ANC)system mainly includes reference sensors,secondary sources and error sensors.The location of error microphones is one key factor that determines the performance of an ANC system in terms of global sound power reduction when the number and the location of secondary sources are fixed.This thesis aims at near field acoustic error sensors arrangement for active sound radiation control in free field.First,the error sensor location in single channel ANC systems is investigated.The optimal near field error sensor location at low frequency is analyzed analytically based on the monopole,dipole and multipole primary sources.Simulation results show that good noise reduction performance can be achieved by locating the error microphones between the primary source and secondary sources but closer to the secondary sources.With the increasing of the frequency,the optimal near field error location shifts a little bit to the primary sources.Second,the error sensors location in multichannel ANC systems is investigated.With secondary sources uniformly distributed on the sphere,the optimal error sensor location of multichannel system at low frequency is derived analytically based on a monopole primary source.Simulation results on different kinds of primary sources such as monopole,different size of dipoles and multipoles obtain the optimal near field error sensor location in each case and the relationship between the optimal location and the type of primary sources.The control mechanism with the error sensor at optimal location is explored by comparing the distribution of sound pressure level both on the error sensor surface and the whole sound field with and without control.Finally,the multichannel ANC experiment is conducted in an anechoic room based on the dipole primary source and tripole primary source.It seeks for the optimal error sensor location by measuring the noise reduction with the error sensor locating at different position on the lines connecting the primary source and secondary sources.The experiment results in 4-channel 8-channel and 12-channel ANC systems validate that the optimal error sensor location is locating between the primary and the secondary sources and the results match well with the analytical and simulation results.