ASA 127th Meeting M.I.T. 1994 June 6-10

2aEA10. Spark-driven Helmholtz resonator.

Kenneth D. Rolt

John L. Butler

Image Acoustics, 97 Elm St., Cohasset, MA 02025

George Cavanagh

Massa Products Corp., Hingham, MA 02043

Spark sources are among the oldest natural sources of electroacoustic transduction, with the most dramatic example being lightning and the resulting thunder in aeroacoustics. In underwater acoustics, W. P. Mason conceived a method for using the spark as a sonar source in a 1946 U. S. Patent 2,403,990. Mason envisioned it as a source of broadband acoustic energy, which was then filtered passively by a housing to narrow the spectrum of the sound pulse. Nearly 50 years later a different method is envisioned for obtaining a coherent sonar pulse from an underwater spark source, by using the spark to drive a Helmholtz resonator. This approach attempts to match the impulsive nature of the spark source to the natural vibration mode of the resonator, rather than by Mason's filtration method. The design layout, electroacoustic model, and preliminary results for 1 424-Hz, 200-J (input) spark-driven Helmholtz transducer having a Q of (approximately equal to)35 will be shown. [Work partially supported by SBIR Topic N92-088, under Contract No. N66604-92-C-0409.]