Depth-dependency of bulb implosions as a low-frequency sound source

Measurements of a depth-dependent characteristic of light bulb implosion in shallow water are presented. Incandescent bulb 500W was used as a sound source and its height and width are 12, 11 cm, respectively. A number of time series, which were imploded at less than depth of 100 m, were obtained by a hydrophone and high resolution analog-to-digital converter. Subsequent negative and positive pressure pulses in a time domain were well defined. As imploding depths are deeper, bubble pulse periods are decreasing in time. This phenomenon gave a significant impact on the primary resonant frequency caused by bubble oscillations. The main energy is concentrated in the frequency range of 100 to 500 Hz. The energy spectral densities in this band show the value of 170 to 185 dB (re 1μPa²sec/Hz @ 1m). Semiempirical relationships were derived from the time and frequency domain data and compared to the result reported in previous studies. Some differences are found in accordance with imploding depth. Possible causes for this are presented. This paper provides useful criteria to researchers who are going to use imploding light bulbs as an acoustic source.