David L. Gardner
CDR, NOAA Pacific Marine Environmental Lab., 7600 Sand Point Way, N.E., Seattle, WA 98115
Thomas B. Gabrielson
NAWC Aircraft Div., Warminster, PA 18974
Several geometries for low-frequency underwater calibrations are in common use, but often require either anechoic walls, rigid walls, or tanks (or lakes) of large dimensions with respect to a wavelength. Such facilities are frequently not practical for use in teaching laboratories either because of inaccessibility or because the facility must be shared with active researchers. The compliant, water-filled cylindrical tube described in this paper permits low-frequency calibrations in a laboratory environment, with modest cost and size. The sound speed inside one such device is approximately 300 m/s, which allows 100-Hz measurements in tubes 1 m long. The limitations of the compliant tube calibrator and examples of measurements made using the calibrator will be discussed.