Volume 118, Issue 3, September 2005
Index of content:
- ACOUSTICAL MEASUREMENTS AND INSTRUMENTATION 
118(2005); http://dx.doi.org/10.1121/1.1979447View Description Hide Description
For thin nonlocally reacting porous layers, a method derived from the work of [Chien and Soroka, J. Sound Vib.43, 9–20 (1975)] has been used to localize the pole of the reflection coefficient located at a complex angle close to and to measure the surface impedance at this angle. Measurements are performed with a small source/receiver separation. The method is used in the present work to measure the surface impedance of acoustically thick porous layers of high flowresistivity. Simulations show that the measured impedance, which is related to a complex angle close to like for thin porous layers, is close to the impedance at grazing incidence. It is also shown that for semi-infinite layers the method provides a measure of the Brewster angle of the medium. Measurements of the cosine of the complex angle and of the related impedance on two granular media of high flowresistivity, Ottawa sand and glass beads, are in a reasonable agreement with predictions for frequencies above for a source/receiver separation of .
118(2005); http://dx.doi.org/10.1121/1.1984860View Description Hide Description
The dominating method of measuring sound intensity in air is based on the combination of two pressure microphones. However, a sound intensity probe that combines an acoustic particle velocity transducer with a pressure microphone has recently become available. This paper examines, discusses, and compares the two measurement principles with particular regard to the sources of error in sound power determination. It is shown that the phase calibration of intensity probes that combine different transducers is very critical below 500 Hz if the measurement surface is very close to the source under test. The problem is reduced if the measurement surface is moved further away from the source. The calibration can be carried out in an anechoic room.