Analysis of the radiation from the violin f-holes using patch near field acoustical holography

Abstract

Although differential pressure measurements offer a direct means to understand the energy flow from the f-holes of the violin they have been performed only at discrete frequencies over relatively limited portions of the acoustic field, and none have ever covered an entire f-hole over a broad frequency region. Application of recently developed near field acoustical holography (NAH) patch processing techniques to 108-node planar rectangular grid microphone data provides a powerful tool to understand the flow of acoustic energy from the f-holes up to 4 kHz. The grid covered each f-hole as well as a small portion of the violin top-plate and provided the necessary spatial resolution to allow isolation of only f-hole aperture radiation in the NAH processing. The projected radiativity in the far field at 1.2 m from just the f-holes was compared with prior microphone measurements in an anechoic chamber over an entire sphere around the violin. As expected the lowest cavity mode A0 was the major radiator at the frequencies below all the corpus modes. Surprisingly the first corpus bending modes appear to radiate strongly through the f-holes also. [Work supported by ONR and NSF.]