WEINSTEIN: EXPLOSIVE SOUND-SOURCE STANDARDS 



DISCUSSION 



Dr. D. V. Wyllie (Weapons Research Establishment (WRE) , Adelaide, 

 South Australia) : We are very interested in propagation-loss measure- 

 ments using explosive charges as sound sources. We are also concerned 

 with the difficulty in assigning a precise source level to these charges 

 at frequencies around 20 Hz. Third-octave bands are unsuitable for use 

 at these frequencies since they are too narrow and the resultant source 

 level too uncertain. In our measurements we shall be employing octave 

 bands. However, the source level still remains a problem. 



Something we have considered is changing the pressure signature of 

 the charge through the use of explosives other than TNT. There are 

 groups within WRE interested in pursuing this approach. 



Since the variation in level in narrow bands at low frequencies 

 results from the interference between the radiation from the pressure 

 and first-bubble pulse, the use of rocket propellant as the explosive 

 could modify the pressure signature of the charge sufficiently to reduce 

 level variations at low frequencies. The pressure signature can be 

 modified by varying the burn rate of the explosive. The resulting 

 explosive may be more useful at low frequencies. Ms. Christian, are 

 you aware of previous work along these lines and would you like to comment 

 on the approach? 



Ms. E. A. Christian (Naval Surface Weapons Center) : The fact is, 

 yes, you certainly do have materials which have slower detonation (or 

 burning) rates than typical HE materials. But the only way I have ever 

 heard of for really eliminating this ungainly bubble pulse is through 

 some mechanical method of breaking it up or venting it out. You can 

 arrange to have a natural venting, as has been done by Woods Hole for 

 many years; that is, you can fire the charge near the surface, shallow 

 enough so that the bubble blows out and it isn't there to bother you. 



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