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Design of Acoustic Absorbers Using Perforated Boards
Jun, David ; Stejskal, Pavel (referee) ; Kalousek, Lubor (advisor)
Perforated boards are one of the most commonly used elements for the construction of acoustic resonators in the form of walls or ceilings. This diploma thesis focuses on some aspects of the design of these perforated resonators. The main factor considered was the shape of the holes in the plate and its influence on the measured course of the sound absorption coefficient and also on its prediction by commonly available methods. The first aspect of resonator design is to measure the sound absorption coefficient. Within the work, common measurement methods are thoroughly compared and the reverberation room method, which is further used for measuring the produced samples, is presented in more detail. For the purposes of this part, our own hardware and software solution of the measuring set is also developed. Service scripts were written in the Python programming language. The second aspect of the design treated in this work is the choice of the porous infill of the resonator based on its value of airflow resistivity. This value is determined here by the static airflow method and based on the relevant standards, our own measuring device was developed for these purposes. This device was made mainly by FDM 3D printing and was operated by scripts in Python. The third and last of the design aspects described here is the prediction of the course of the sound absorption coefficient of perforated resonators. In this part, the method of electro-acoustic analogy is presented together with the transfer matrix method as described in the literature, which is further supplemented by the introduction of an equivalent radius including the effect of hole elongation in the calculation. The results obtained by the calculation are finally compared with the measurement and the optimization of the calculation is proposed in the form of adjusting the relationship for the end correction factor and for the combination of acoustic impedances of individual layers.
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