66 Lecture 3 
high explosive shock. The total energy in the pulse from the slow-burning ex- 
plosive is much less than for the high explosive. Thus, the former may be re- 
garded as a low-efficiency acoustic source, whereas it is unlikely the efficiency 
value of about 50% for a high explosive could be much improved. The pulses from 
the two explosive types have a comparable impulse and, therefore, comparable 
low-frequency energy, but the rounded pulse produces negligible high-frequency 
energy. Also the gas bubble from the slow material does not greatly overshoot 
its equilibrium radius, so there is little bubble oscillation and very little energy 
in the bubble pulse. Since the bubble pulses contribute a good proportion of the 
low-frequency energy for high explosives, thenet resultis that the slow material 
is down over most of the spectrum (very low frequencies have not been investi- 
gated and could be an exception). 
