Medição do coeficiente de espalhamento em câmaras reverberantes em escala reduzida e escala real

Abstract

The study of diffusion and sound scattering is relatively new in acoustics. Diffusers were first proposed as acoustic treatment in the late 1970s and only gained widespread popularity in the market about ten years later. Considering the importance of parameters such as the scattering coefficient for a better acoustic characterization in simulations and the limited existing database on the subject, a long journey of study and research in the area of acoustic diffusion can be envisaged. Thus, the present work aimed to experimentally evaluate the effects of diffuse reflections and their relationship with the scattering coefficient, through measurements standardized by ISO 17497-1, which provides guidelines for testing in a reverberation chamber. The study covers fundamental aspects, including the technical and practical aspects of the tests and a detailed analysis of the construction of the necessary apparatus for the measurements conducted in physical scale model (1:5) and full scale. To enable the full scale testing, it was necessary to design a rotating table for sample placement, as well as to set up the measurement chain for both model and full scale tests. Therefore, this work discusses the scattering coefficient, the experimental testing, its challenges, and the results obtained for the tested samples. For the model, the adaptations achieved the expected objectives. However, in the full scale measurement, the need to improve the design and reduce the absorption of the rotating table at low frequencies, especially in the 800 Hz band, was identified. Other improvements, such as motorization in the table rotation method, were suggested to obtain more accurate results and shorter tests. These considerations emphasize the importance of continuous improvements in the measurement system to enhance precision and reliability of results in both scales, enabling future more well-founded studies. Accordingly, this work provided a setup for analyzing the scattering coefficient in full scale measurements, paving the way for further studies on the topic of sound scattering, and also enhancing the scale model chamber, providing continuity in the research on sound scattering in the Acoustic Engineering course.