The measurement of acoustic impedance at oblique incidence with two microphones

A new method for measuring normal acoustic impedances in oblique incidence is suggested which allows the use of white noise. The measurements are performed very close to the surface of the material, so that samples of about one square meter may be used for frequencies higher than 500 Hz. Two electret microphones are employed. The method has been tested by measuring the impedance for oblique incidence at 2000 and 3000 Hz for a Climaver glass fiber. Good agreement is found between theoretical prediction and experiment. The measured impedances appear to be correct up to 80 deg for the frequencies 2000 and 3000 Hz. (C.D.)