Study of a concert harp's radiation using acoustic imaging methods

Recent studies have been conducted to understand the low frequency radiation of a concert harp. Experiments have been carried out in a semi-anechoic room: the harp's soundboard is excited with a shaker and the pressure is measured at more than 600 positions on a nearly hemispherical surface at a distance of about 2 m from the instrument. Simple source models with a set of monopoles have been optimized to fit the measured acoustic radiation. These models are very satisfactory in the low frequency domain but cannot properly reproduce the measured field above 350 Hz. The aim of this paper is to present the application of acoustic imaging tools to this academic case: volumetric velocity and acoustic power maps in the harp plane are computed with an optimized beamforming and with a regularized inverse FRF method up to 1 kHz. The optimization of the beamforming is realized using a variable windowing factor, and the regularization of the inverse FRF method with a Tikhonov approach. The presented results permit the evaluation of the importance of the bass reflex effect in the harp, of the contribution of the first bending modes and of the contribution of the soundbox vibrations in the radiated sound field.