Análise de parâmetros relacionados à difusão de campo acústico em recintos fechados

Abstract

Noise attenuation and control is an important attribution of engineers, because noise pollution may harm the lives of people or disturb the balance of biological systems. Handling and acoustic treatment as a way to not only control sounds, but to distribute them in the best possible way in the enclosures is also an issue targeted by acoustic designers. In order to carry out consistent studies it is also of great importance that acoustic parameters of materials be known and have good reliability, as well as some concepts that involve this area of knowledge. One of the issues that has generated a recent discussion concerns the so-called "diffuse acoustic field." A diffuse field is necessary, for example, for measurements of sound absorption coefficients, sound power and sound insulation, all in reverberant chambers. Due to the lack of good parameters to describe this assignment of an acoustic field, some authors have been developing more adequate methodologies than those currently used. The present work aims to verify some of these methodologies. Impulse responses (transfer functions) were measured and analyzed in a real-scale reverberant chamber and in a reduced model, with and without the use of diffusers and absorptive samples. With the data obtained some indicators, such as standard deviation of sound pressure level, kurtosis factor and deviation of uniform distribution of the phase of transfer functions, have been calculated and used for comparative purposes. It is noted that the standard deviation of sound pressure levels is related to the metrics obtained from the transfer function, and is related to the homogeneity of the sound field. The kurtosis analysis on impulse responses in the time domain is related to homogeneity and isotropy of the sound field. This metric also indicates that the addition of absorbers tends to worsen the diffusion of the acoustic field while the addition of diffusers tends to improve this characteristic. The analysis of the phase distribution of the transfer functions demonstrates to be related to the transition frequency, which can be more clearly identified with the kurtosis of the transfer functions, in the frequency domain.