Using nearfield holography to study energy flow from musical instruments

Abstract

We have developed a technique called nonwavelength limited, or nearfield, acoustical holography that can experimentally determine the radiated pressure field, particle velocity field, and the vector intensity field of low-frequency (below 1500 Hz) sound sources where the source is often smaller than a wavelength. Mappings which show the rate and direction of the acoustic energy flow from the source (nearfield) out to the farfield may be constructed. These mappings are valuable for locating sound sources and determining their strengths. Most of our early work focused on relatively simple sources, but recently we have been looking at more complex sources such as musical instruments, specifically guitars and cellos. The instruments are intact and string excited. Holographic reconstructions of the top of the guitar show both the plate motion and the motion of the air in the rose. Preliminary results indicate that the rose is a dominant source of the radiated sound energy over the first two octaves of the guitar's range. Maps of the energy flow around and away from the instrument will be presented.