Laser Doppler vibrometry and near-field acoustic holography: Different approaches for surface velocity distribution measurements

Nowadays there are several direct or indirect measurement methods for the determination of the surface velocity in vibrating structures, but two of them seem to be the most promising and interesting, in particular for vibro-acoustic problems: laser Doppler vibrometry (LDV) and near-field acoustic holography (NAH). While LDV is a direct laser-based vibration measurement technique, NAH allows the determination of the particle surface velocity starting from simultaneous microphone measurements performed on a plane array positioned near the vibrating object, although with some limitations. In this work the two structural and acoustic techniques are compared on a simple laboratory case, specifically a plate, in order to carefully and quantitatively assess the measurement uncertainty in the indirect NAH method used to estimate the vibration velocity. Advantages and disadvantages of the two methods are discussed briefly. This study was conducted within the European Growth Project “ACES” (Optimal Acoustic Equivalent Source Descriptors for Automotive Noise Problems) GRD1-1999-11202.