ENERGETICS OF SPEECH 329 



this are attained by a shortening of the vocal chink. In the small 

 or head register the notes are produced by vibrations of only the 

 inner margins of the cords, and the vocal chink is reduced to a 

 small anterior aperture which becomes smaller as the pitch rises. 

 These different mechanisms produce tones of perceptibly different 

 quality. 



Timbre or quality of the voice depends largely on the accessory 

 resonating chambers. These cavities pick out and accentuate 

 the overtones produced by the vibrations of the segments of the 

 cords. Trained singers consciously or instinctively adapt the 

 shape of the mouth so as to secure for each tone the most suitable 

 overtones. 



The work done in speaking and in singing is complex. Many 

 muscles are brought into play and the energy expended by them 

 varies with the rate of speech and the intensity of the sound 

 produced. The pressure of air employed in ordinary quiet con- 

 versation amounts to between 140 and 240 mm. of H 2 O, while 

 nearly 1000 mm. are required when shouting is indulged in. 



If work (phonation only) is taken as equal to the product of 

 the pressure and volume of air expelled, i.e. W =VH, we may 

 make a rough assessment of the amount of work done. During 

 ordinary conversation, a man with a tracheal cannula developed 

 an air pressure of 100 mm. (H 2 O) and expired 300 litres of air 

 per hour i.e. 



300 xlOO 

 VH =- =3 kgm. per hour. 



Speaking in a large hall the same man expired 1440 litres of air 

 per hour and developed a mean pressure of 150 mm. (H 2 O), 



W =1440 xO-15 =216 kilogrammetres. 



One may arrive at an estimate of the work of speaking by 

 measuring the oxygen used during rest and during speech. 

 Delivering an oration at the rate of 150 syllables a minute 

 caused the consumption of 28-78 litres of oxygen. Subtracting 

 from this the amount used during a similar period of rest, viz. 

 16-96 litres, we find that 11-82 litres were used by the orator. In 

 large Calories this amounts to 11-82x4-9=57-9 Cals. per hr. 



57 -92 



In kgm. this gives - - x 425 =6154 kilogrammetres. 

 4 



The value just obtained is about 15 times as great as that 

 of mere phonation. We must remember that the orator, and 

 the subject of the experiment was a Frenchman too, uses many 



