A new laser vibrometry-based 2D selective intensity method for source identification in reverberant fields: part I. Development of the technique and preliminary validation

The selective intensity technique is a powerful tool for the localization of acoustic sources and
for the identification of the structural contribution to the acoustic emission. In practice, the
selective intensity method is based on simultaneous measurements of acoustic intensity, by
means of a couple of matched microphones, and structural vibration of the emitting object. In
this paper high spatial density multi-point vibration data, acquired by using a scanning laser
Doppler vibrometer, have been used for the first time. Therefore, by applying the selective
intensity algorithm, the contribution of a large number of structural sources to the acoustic
field radiated by the vibrating object can be estimated. The selective intensity represents the
distribution of the acoustic monopole sources on the emitting surface, as if each monopole
acted separately from the others. This innovative selective intensity approach can be very
helpful when the measurement is performed on large panels in highly reverberating
environments, such as aircraft cabins. In this case the separation of the direct acoustic field
(radiated by the vibrating panels of the fuselage) and the reverberant one is difficult by
traditional techniques. The first aim of this work is to develop and validate the technique in
reverberating environments where the location and the quantification of each source are
difficult by traditional techniques. The reverberant field is clearly challenging also for the
proposed technique, affecting the achievable accuracy, mainly due to the fact that coherence
between radiated and reverberated fields is often unknown and may be relevant. Secondly, the
applicability of the method to real cases is demonstrated. A laboratory test case has been
developed using a large wooden panel. The measurement is performed both in anechoic
environment and under simulated reverberating conditions, for testing the ability of the
selective intensity method to remove the reverberation.