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.

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.

Telephone scheme for the deaf [43.66.Ts, 43.88.Si] A telephone-communication scheme for the deaf proposed by W. H. Brown of JFK Space Center would use existing tone-encoded telephone equipment to transmit messages. The only special equipment required is a decoder at the receiving telephone. A deaf person, if able to speak, could verbally instruct a hearing person at the other end how to transmit messages.

Nearfield acoustical holography (NAH), a process developed at the Pennsylvania State University, has proved itself to be a powerful research tool in the study of single-frequency sound sources. A new high-speed data aquisition system has been developed which permits extension of the nearfield acoustical holography technique to the study of wideband noise sources. Using a partially parallel, partially sequential sampling network, near simultaneous sampling is achieved for 256 microphones in the holographic measurement plane, for acoustic frequencies up to 1500 Hz. Special problems encountered during the development of the high-speed data aquisition system are discussed. [Work supported by ONR and NASA.]

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