Experimental acoustic testing: identifying noise sources with nearfield acoustical holography

The Nearfield Acoustical Holography (NAH) can be applied as a powerful technique for locating sound sources in reflective interior spaces. Measurements made in a sport-utility vehicle interior illustrate the effectiveness of this technique in a more practical environment. In this test, a shaker was attached to the floor pan of the vehicle to simulate the vibration of an exhaust mount point on the floor pan. The shaker was driven with random energy over the frequency range from DC to 400 Hz. A microphone grid with spacing of 86 mm and 67 mm in the x-axis and y-axis was employed to cover the entire floor pan in a 16 × 32 measurement grid. A sub-array of Acoustical microphones traversed over the grid 16 times comprise the entire grid. Results of the test have shown the ability of NAH to locate the source of excitation to a high degree of accuracy.