Comparison of different measurement technologies for the in-flight assessment of radiated acoustic intensity

Abstract

Near-field acoustical holography (NAH) microphone array measurement technologies are currently being investigated for use in aircraft for determining the sound intensity that is radiated through a trimmed aircraft fuselage. Two types of microphone array geometries are studied in this effort, spherical and conformal to the sidewall. Due to the complexity of the interior sound field and in-flight excitation, questions have arisen concerning the capability of array techniques to measure these desired acoustic quantities. The main questions relate to the agreement between array measurements and traditional two-microphone intensity probe measurements and the sensitivity of array measurements to backside sources present in the aircraft cabin. Thus, an investigation was performed in which the NAH array results were compared to intensity probe results measured in the NASA Langley Structural Acoustic Loads and Transmission facility, the Boeing Interior Noise Test Facility, and in flight on the NASA Aries 757 aircraft. An overview of this test sequence and a comparison of NAH, IBEM, and two-microphone intensity probe measurements are made. These comparisons show the relative behavior of the different measurement techniques in both idealized laboratory and realistic in-flight environments. Conclusions are drawn concerning the use of array measurements to assess the sound intensity transmitted through an aircraft sidewall in-flight.

Volumetric acoustic vector intensity imager

“…The data set we report on here is a small subset of a much larger recent experiment using this aircraft. 22 In this experiment most of the seats in the aircraft were removed as well as the trim panels and insulation in four adjacent window sections as shown on the right in the figure. Also shown, but not reported on here, is a conformal nearly planar array of microphones located between the spherical array and the fuselage panel.…”