New Sound Absorption Improvement Strategy for QRD Element

The sound absorption performance and the frequency response of quadratic residue diffuser (QRD) element was investigated using a laboratory experiment. An array of constrained length thin tubes was attached to the inner side of perforated panel for shifting the frequency response of the QRD element purposes. This new coupled structure gives two significant advantages. Firstly, it increases  the value of oscillating mass inside orifices which is the increasing energy loss due to viscous damping mechanism without any changes on porosity of the perforated panel. Secondly, it also changes the response of QRD element to act as a single cavity Helmholtz resonator with multiple extended necks instead of cavity backed perforated panel. As a results, the proposed strategy gives a significant improvement on the sound absorption coefficient of the QRD element especially on the low and mid frequency range without any changes on its basic shape and dimension.

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