DIRECT AND ACCURATE MEASUREMENTS OF ACOUSTICAL IMPEDANCE OF THE MICROPERFORATED PANEL

Microperforated panel absorption constructions are simple in construction, versatile in application, with good absorbing properties a nd afford prediction and design with relatively good accuracy. Their performance depands mainly on the acoustical resistance and mass of the microperforated panels. The exact properties of the microperforated panel, therefore, are necessary in order to estimate the performance of the microperforated panel construction reliably. In this paper, a simple and direct method of impedance measurements for microperforated panel (also suitable for ordinary perforated panels and in a limited sense for other absorbents) is proposed. Better accuracy is attained because of the straightforward nature of the resistance and reactance determination, avoiding the complex transformation of transcendental functions. When applied to actual panel, new light is shed on the nonlinear properties of the acoustical impedance of small apertures and microperforated panels. Preliminary results are presented.