CHRISTIAN: THE ACOUSTIC OUTPUT OF EXPLOSIVE CHARGES 



pressure history for a 1.8-pound TNT charge at 800-foot depth. This 

 curve (1) was "clipped" at 50 percent of the peak value (curve [2]), 

 and again at 10 percent of the peak value (curve [3]) by the computer. 

 We assumed the most amiable system imaginable, and calculated the 

 spectrum levels in 1/3-octave bands for the two "clipped" records. 

 The resultant decreases in levels at the low- frequency end of the 

 spectrum are tabulated at the bottom of the figure.* When clipped 

 at 50 percent of the peak — a matter of a few dB — the resultant 

 error had reached 1 dB in the 250-Hz band. With a 10 percent of peak 

 clipping, the error was twice our desired 1 dB even down at 35 Hz. 

 Perhaps down at even lower frequency — one Hz or so — the 10 percent 

 clipping would not matter. But I think clipped records have to be 

 handled cautiously. And remember that the possible distortions im- 

 posed by a system without instantaneous recovery are not included in 

 this example. 



Charge Configuration. The variations in explosion pressure 

 fields that we can achieve simply by distributing our explosive mate- 

 rial in different configurations is a complex subject that I will not 

 even try to touch on today. This discussion is limited to compact, 

 consolidated, "point" charges that are omnidirectional. But if you 

 want to modify your spectral energy distribution with a given weight 

 of explosive, the quickest way is through charge configuration, and 

 we know a fair amount about the subject. 



Explosive Composition. We can accomplish some redistribution of 

 spectral energy through choice of explosive composition. The bubble 

 fundamental frequency is a function of the charge weight, the charge 

 depth, and a material constant. The constants do not differ 



* The positive values in parentheses for 25 Hz are spurious and mirror 

 our failure to do a DC leveling when we clipped the wave. 



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