Using three microphone array configurations at two aircraft body stations on a Boeing 777-300ER flight test, the acoustic radiation characteristics of the sidewall and outboard floor system are investigated by experimental measurement. Analysis of the experimental data is performed using sound intensity calculations for closely spaced microphones, PATCH Inverse Boundary Element Nearfield Acoustic Holography, and Spherical Nearfield Acoustic Holography. Each method is compared assessing strengths and weaknesses, evaluating source identification capability for both broadband and narrowband sources, evaluating sources during transient and steady-state conditions, and quantifying field reconstruction continuity using multiple array positions.

Transmission loss is an important metric used to assist in the selection of materials for noise control and design. In order to assess and improve the performance of transmission loss measurements, two different techniques were compared: traditional microphone and/or matched pair microphone intensity anechoic chamber-side techniques, and nearfield acoustical holography techniques. Intensity and sound power measurements using traditional methods were made on a test panel installed in an anechoic-reverb facility transmission loss window, then repeated using a conformal nearfield microphone array and nearfield acoustical holography processing techniques. The full vectored intensity components were used to assess the radiation characteristics of the test panel. This assessment quantifies the acoustics as panel radiation, flanking path contamination, and boundary effects. Data are presented to qualify the best estimate for transmission loss by rejecting contamination. Also, the dynamic range of the transmission loss measurement is compared between traditional and nearfield acoustical holography techniques with high transmission loss panel samples.

Near-field acoustical holography (NAH) microphone array measurement technologies are currently being investigated by NASA, the Naval Research Lab (NRL) and Boeing. One type of array geometry under investigation is a spherical arrangement of microphones that enables the computation of the intensity field surrounding the sphere using spherical NAH theory. Due to the simplicity of the required computation and the ability to pre-compute several of the required quantities, the intensity field in a volume surrounding the sphere can be reconstructed and rendered in real time as a measurement is being made. Thus, sound sources can be identified in real time by roving the spherical array around in a sound field near suspected sources and tracking the sound intensity back to the source. This presentation demonstrates the capabilities of a real time spherical NAH system that has been developed by NASA, the NRL and Boeing. The topology of the software will be discussed and the capabilities of such a system will be demonstrated.