Recent studies of an intact string-excited guitar have shown that the motion of the air in the rose is quite significant over the first two octaves of the instrument's range. Our nearfield holography technique has revealed that the rose is a dominant source of the radiated energy. We have found that modeling the guitar as a rigid cavity with flexible top plate and a sound hole is not accurate. The motion of the back plate in the guitar studied was quite significant, with amplitudes across it 2–3 times greater than at the top for the lower frequencies, and therefore should not be ignored in subsequent studies. Additionally, accepted plate modes seem to occur at more than one frequency in the string-excited guitar. The recurrence of these modes may tend to smooth out the frequency response curve, and a better understanding of this effect may lead to a more well balanced instrument.

A study of a violin's vibration and radiation characteristics has been undertaken using two techniques. The goals of the study are to perform a modal analysis of the instrument and to use the nearfield acoustical holography (NAH) system located at the Pennsylvania State University to reconstruct the instrument's radiated sound field. The modal analysis will locate the various resonances of the top and back plates and show the relative motion of the plates. The NAH system will locate those areas on the instrument that produce the energy that radiates to the farfield. This paper will discuss the work completed to date and present the results obtained from this work.

The mechanical responses of three freely supported guitars have been studied both under impulsive excitation and under excitation with a sinusoidal force [J. Popp and T. D. Rossing, J. Acoust. Soc. Am. Suppl. 1 76, S26 (1984)]. The normal modes of vibration as determined by the two different methods have been compared, and the agreement is found to be quite good. A comparison is made with the modes of vibration recorded in one of the guitars with the ribs fixed using time-average holographic interferometry.

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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.