Desenvolvimento de um sistema automatizado para medições de funções de transferência entre microfone e fonte sonora

Abstract

With advancements in signal processing technology and in the computational capabilities of equipment, new technologies can be implemented in the analysis of room acoustics. Using a robotic arm to position a microphone in the space, a virtual automated microphone array can be formed more flexibly than a rigid array. The application of this type of array to perform room impulse response measurements allows for the measurement and analysis of characteristics of the room, which in turn produce a better understanding of its behaviour and the factors that influence it. Given the linearity and time-invariance characteristics of acoustic systems and using already established tools and methods, the objective is to develop a system capable of reproducing an automated microphone array. The transducer’s positioning is done using a robotic arm and the room impulse response is measured using the deconvolution method. Initially, the main application of this system is to calculate and analyse the wavenumber spectrum of the room’s sound field. Due to the robot’s specifications, the system also could inform about positions that may not be achieved by the robot, by calculating and verifying its inverse kinematics. The proposed architecture is of a MATLAB controlled system that sends commands to the robot through serial communication and performed transfer function measurements through a sound interface. The measurements use an appropriate transducer that is held by the robot using a 3-D printed holder. A support library for the communication and inverse kinematics has been developed. The designed arrays were unidirectional and source-pointing spherical arrays and unidirectional random position arrays. Tests were conducted in a common room, in which the parts and integration were verified. Thus, the achieved system has been able to acquire data for reverberation time, Schroeder’s frequency and critical distance analysis, assuming a lightly damped environment. The analysis reveal coherence with statistic acoustics theory. The system was used to measure the room impulse responses for its normal (light) damping condition and with a 10,8 m2 glass wool absorbing sample. The wavenumber spectrum and the surface absorption for the damped environment were calculated. It can be verified between 500 Hz and 2 kHz that there are spurious reflections, possibly due to the irregular nature of the room’s surfaces. The absorption of the glass wool calculated using the wavenumber domain showed an erratic behaviour but tending towards the behaviour of a porous material absorber. The comparison between a reconstructed RTF for a certain microphone position and a measured RTF in the same position reveals that the plane wave decomposition was successful.