372 BELL SYSTEM TECHNICAL JOURNAL 



playing with full Aolume will produce peak acoustic powers as great 

 as 70 watts. 



When such an orchestra played the four different selections, the 

 maximum peak powers varied from 8 to 66 watts, but the average 

 powers were .08, .07, .07 and .13 watts, respectively. Hence the 

 variation of the average power from selection to selection was much 

 less than that of the peak power. Both the peak powers and also 

 the average powers for the orchestra are about 10,000 times the 

 corresponding powers for conversational speech. In Fig. 20 the curves 

 show how the peak power was distributed among the different pitch 

 bands for this 75-piece orchestra. The curves give the average values 

 for the four selections. The zero line corresponds to a power of 

 approximately 1/lOth of a watt. The levels correspond to that which 

 was obtained in the half octave band acting alone. Although the 

 maximum peak was 70 watts for the unfiltered music when the heaviest 

 piece was being played, the most probable peak value in any half 

 octave band is less than 1/10 of a watt except for the octave between 

 - 2 and - 1 octaves, where it is slightly higher than this value. 

 The distance between the two curves increases as you go to either 

 side of this octave which is approximately that between middle "C" 

 and the "C" above it. This indicates that the components in this 

 region are more nearly alike in intensity and occur more frequently 

 than in the other regions. The top curve indicates that from the 

 standpoint of maximum peak values the half octaves from — 2| to 

 + 1| octaves are all about equally important. As the pitch of a 

 component goes below 2\ octaves, its intensity decreases rapidly as 

 indicated in the figure. Very intense peaks occur occasionally with 

 frequencies as high as 10,000 or 12,000 cycles. 



To find the lowest level used in orchestral music a violin player was 

 asked to play as softly as is ever customary while playing before the 

 public. Its average power was found to be about 4 microwatts. It is 

 thus seen that the peak power from a large orchestra is about 

 20,000,000 times the average power produced by soft violin playing. 



Audible Pitch Limits for Musical Sounds 



Measurement of the detectable pitch limits was determined in a 

 way similar to that described for conversational speech. The results ^ 

 for typical musical instruments are shown in Fig. 21. For comparison 

 the results for speech and some common noises are also included. 

 It will be seen that the lower limit for music is determined by the bass 



' A more comprehensive report of this work will soon be given in a paper by W. 

 B. Snow. 



