CHRISTIAN: THE ACOUSTIC OUTPUT OF EXPLOSIVE CHARGES 



for a few minutes and talk about an explosion wave as it really is , 

 rather than as acousticians would like it to be. 



Desirable attributes of sources for use in low-frequency acoustic 

 work are much the same, whether the sources are CW transducers or are 

 explosions. For use in the field it is desirable to have sources that 

 are reliable, inexpensive, with a high energy output at the desired 

 frequency range, and convenient and simple to operate under field test 

 conditions. For use in data analysis, it is desirable to have known 

 standard source levels, source level values that are compatible with 

 the sonar equation, and values that are predictable within some speci- 

 fied decibel allowance in a narrow-band frequency. Explosion sources 

 often come out ahead when considering field-use desirability, which 

 is why they are used so widely for underwater acoustics research. But 

 for the analysis end of the problem, explosions sometimes seem to be 

 intractable. Today I will show you some of the reasons this is so. 



For today's discussion, let me use values of bandwidths and fre- 

 quency ranges and prediction errors that I have heard discussed within 

 the past year as being desirable in acoustics research work. (It may 

 be that during the course of this Workshop these values will be modi- 

 fied. If that is the case, I will only say that I hope all of them 

 will increase, from the point of view of our ability to utilize avail- 

 able information today. ) We would like source levels in 1/3-octave 

 bands. And we want these levels to be predictable to within 1 dB, 

 over the frequency range of 10 to 300 Hz. Here I purposely use the 

 word "predictable," rather than "reproducible" to within 1 dB. Repro- 

 ducibility is not the problem with the explosive compositions usually 

 used in acoustics work. If you replicate the experiment — the charge 

 type and depth, the measurement point, the recording and analysis 



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