Nearfield Acoustical Holography (NAH), Statistically Optimized Nearfield Acoustical Holography (SONAH) and the Equivalent Source Method (ESM) are widely used in noise source identification. NAH requires the sound field to fall to negligible levels at the edges of the measurement aperture, a requirement rarely met in practice. As a result, SONAH and ESM have been developed. In addition, the Inverse Boundary Element Method (IBEM) can be used, given sufficient computational resources. Unfortunately, none of these methods directly guides the changes necessary to reduce noise radiation. Radiation mode analysis has previously been primarily associated with forward prediction of radiated sound power. Since radiation modes contribute independently to sound power radiation, it is only necessary to modify the surface vibration so that it does not strongly couple with those modes in order to ensure sound power reduction. Since the radiation modes can be used as the basis functions through which the surface motion of a source can be described, an inverse method based on radiation modes allows the surface vibration that results in the majority of the radiated sound power to be identified unequivocally, and so will, in turn, guide the design changes needed to reduce radiated sound power.
Nearfield acoustical holography, Radiation modes, Noise source identification
Acoustics and Noise Control
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