Investigation On Robustness Of Acoustic Focusing Loudspeaker Array Under Non-ideal Acoustic Environments

With the rapid development of portable communication devices and intelligent speech interaction devices,users have increasingly higher demand on the performance of audio playback system on these devices.Acoustic focusing characteristics of audio system have attracted increasingly more attention.The sound field reproduction system on portable communication devices can only be realized using compact loudspeaker array due to the limited size of such devices.Acoustic contrast control(ACC)algorithm can focus the sound energy in the bright zone by maximizing the ratio between the mean sound energy in the bright zone and that in the dark zone,which makes it a competitive method to realize sound focusing control using a small number of loudspeakers.Most of the analysis on the acoustic contrast control is based on free-field model.However,the reverberation and scattering are inevitable in most practical applications especially for small scale loudspeaker arrays,and it is meaningful to investigate the robustness of acoustic focusing system in such non-ideal conditions.This thesis focuses on the acoustic performance of acoustic focusing performance based on the loudspeaker array in non-ideal acoustic field,and both reverberation and scattering effects are considered.Firstly the current research on acoustic focusing algorithm and its robustness analysis are summarized.To solve the common problem faced by all the array system,i.e.,the mismatch between the loudspeakers,a calibration method based on Wiener filter is designed and its effectiveness is validated through experiment on 5 loudspeakers.Secondly,a compact sound focusing system using five loudspeakers is established and investigated in simulations.The acoustic focusing characteristics of the loudspeaker array under both reverberation and scattering conditions are investigated by the image model and room impulse response for a rigid sphere.It is found that the robust acoustic contrast control(RACC)method has both good focusing performance and robustness to random disturbance,reverberation and scattering.This means that it is possible to achieve good acoustic focusing performance near listeners' ears in practical applications.Finally,an experimental evaluation system is established,and the robustness of the acoustic focusing system is tested in a room with both reverberation and near-field scattering effects.The experimental results show that the RACC can lead to both good sinusoidal and wide-band acoustic focusing performance.