SCIENTIFIC RESEARCH APPLIED TO THE TELEPHONE 259 



to five hundred. The actual power used in producing the various 

 sounds depends, of course, upon the speaker and the emphasis with 

 which he pronounces the sound. The power in an accented syllable 

 is three or four times that in a similar unaccented syllable. Measure- 

 ments upon a number of voices during a conversation have indicated 

 that the average power in the speech produced is ten microwatts 

 (one one-hundred-thousandth watt). Some speak with more and 

 others with less than this power. In Table I is shown how various 



TABLE I 

 Relative Speech Powers Used by Individuals in Conversation 



voices in a sample group vary from the average. It is seen that 

 seven per cent speak with less than one sixteenth the average power, 

 eighteen per cent use powers lying between one quarter and one half 

 the average, and four per cent between four and eight times the 

 average. No speakers were found to use more than eight times the 

 average for conversational purposes. 



Now let us consider the variations for a typical speaker. As a 

 conversation proceeds, the speech power varies from zero during the 

 silent intervals to peak values which frequently are one hundred times 

 the average power. Extensive measurements of these peak powers 

 upon a number of speakers indicated a distribution about the average 

 as shown in Table II. For example, if we should examine the speech 



TABLE II 

 Peak Powers in Conversational Speech 



Power Boundaries 

 In Terms of Average Power Per Cent of Intervals 



Below 1/8 '. .12 



1/8 to 1/4 4.0 



1/4 to 1/2 4.5 



1/2 to 1 5.5 



1 to 2 8.3 



2 to 4 12.7 



4 to 8 18.6 



8 to 16 17.0 



16 to 32 10.5 



32 to 64 5.1 



64 to 128 1.7 



Above 128 1 



