Evaluation of the accuracy of measurements performed by a spherical array of microphones

Abstract

This Master’s thesis consists in evaluating a spherical microphone array developed in a previous project, which will be referred to later, that aimed to extract 3D Room Impulse Responses with a measurement system composed of the referred microphone, among other tools. We will focus on the accuracy of localization of the sound as a direct continuation of the previous work. It could be considered as the main application of this system, hence it is important to emphasize the need of this evaluation. The measurement system consists of a spherical antenna containing 16 microphones, two cards with 8 channels each and the associated signal treatment. Adobe Audition and the Matlab software are used in order to process the information which is provided by the measurement system. The current aim is to evaluate the precision provided by the system, which is evaluated in several situations. Different acoustics measurements have been taken in an anechoic room and also in a reverberant room. A calibration task can be found and additionally, the first measurements with their corresponding analysis are presented. After that, measurements with pure tones and impulse responses have carried out. In both parts, we focus on the horizontal plane. We introduce the diffuse field measurements using pure tones and pink noise. Then we treat the recorded information to show different diagrams obtained by different beamforming methods. I conclude that there are some unusual results but the microphone array works. The experimental study includes capturing the impulse responses and evaluating of different types of beamforming. We conclude that PWD beamforming works badly in the measurements of this project. We can also say that the sound field in the reverberant room is not really diffuse.