William C. Ward
Los Alamos Natl. Lab., MS-J576, Los Alamos, NM 87545
Thomas B. Gabrielson
Naval Air Development Ctr., Code 5044, Warminster, PA 18974
An experimental thermoacoustic projector (a heat-driven sound source without moving parts) produced source levels near 190 dB at 120 Hz during recent tests at the Navy's Seneca Lake facility. These data were taken near 60 m depth; in thermoacoustic projectors, the source level increases linearly with depth. The device is composed of two coupled vertical tubes. The upper driver tube is filled with helium and contains a thermoacoustic stack with hot and cold heat exchangers. The lower tube is an impedance matching device filled with water up to a variable level. The tube opening is necessarily small compared to wavelength. For a radiation impedance with such a small resistive component, the test device demonstrated a resonant mode ambiguity before reaching the optimum tuning point. This effect reduced the maximum source level by 3--5 dB below the design level, and had a similar effect on the overall efficiency. This presentation will give an overview of the experimental results and introduce design modifications to overcome the observed limitations and reduce the size of the projector as well.