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BELL SYSTEM TECHNICAL JOURNAL 



Relative Power of Speech Sounds 



A direct comparison of most of the fundamental sounds will now be 

 made. In Table V — A are shown the conversational values (averaged) 

 of the mean power for each sound for 16 speakers. The units are taken 

 arbitrarily in order to show only the relative values. As might have 

 been expected, the vowels rank the highest, the semi-vowels next and 

 the consonants the lowest, although we find a few consonants inter- 

 spersed among the semi-vowels. In Table V— B is the similar arrange- 

 ment for the normal values of peak power for the two speakers. Data 

 on a larger number of sounds are available for this group, but the same 

 general order prevails: vowels, semi-vowels and consonants. Minor 

 differences in order (note "v" as in "vat") may be expected to occur 

 because of the influence of stress upon the conversational value. But 

 in both cases the ratio of the maximum to the minimum is of the order 

 of 2000. This similarity is striking in view of the difference in the 

 modes of utterance and the numbers of speakers in the two cases. 



Finally, in Table V — C are shown relative values" derived on the basis 

 of relative attenuation in power required to bring the articulation (as 

 judged by the average ear) to 80%. Since disconnected monosyllables 



/ 



</ 



H 



I — ' 



r 



n 



A 



\ 



\ 



N 



r- 



r- 



y ^ ^ -O O CJ -C3 <D IC - '(J) 



Fig 2. Comparative Chart Relative Normal Values of Vowel Sounds. 



— • Peak Power. 



Mean Power. 



Relative Power Attenuation Required to Give 80% .\rticulation. 



were used in this test the values are normal values in our present 

 category. Although the same general order of the other two tables 



* Taken from the paper presented by Harvey Fletcher before the Modern Lan- 

 guages Association, December 1923. Values are there called relative "intensity" 

 which term we avoid here because of the acoustic meaning already assigned to in- 

 tensity: power per square centimeter. 



