406 



THE VOICE 



oscillatory pressure (R.M.S.) for various frequencies of vibration 

 detectable by the hiuiian ear {q.v.). Starling states that in patients 

 on whom tracheotomy had been performed, the pressure of air in 

 the trachea necessary to cause the production of an audible sound 

 was from 140 to 240 mm. HgO, and for loud shouting a pressure of 

 945 mm. of water was necessary. This pressure is furnished by 

 the contraction of the expiratory muscles {q.v.). 



TABLE LXI 



Notation, Frequency, Pressure and Amplitudes of Air Waves 



OF the Musical Scale 



* In France frequency is mea.sured in single vibrations, and so all the figures in 

 this column are half the French values. 



The first muscular act in breathing for the purpose of phonation 

 is a slight inspiration. When this is done properly, the column of 

 air, resting as it were on the diaphragm, is ready for its impact on 

 the vocal cords, an impact which must be made with the greatest 

 nicety and control. Hudson-Makuen states that the expiratory 

 act necessary for phonation is produced by a contraction of the 

 diaphragm which pulls the lower ribs downwards and inwards, 

 i.e. a muscle which in ordinary breathing is inspiratory, here acts 

 in the opposite sense. Proper co-ordination of the intercostal and 

 abdominal muscles are, of course, just as essential for phonation as 

 for respiration. 



Loudness is due to amplitude of vibration, and depends, in part, 

 on the force and volume of the blast of air emitted. 



In part, it depends on the size of the larynx and of the resonating 

 chambers, and on the tension of the vocal cords. A true cres- 

 cendo is obtained by relaxing the tension of the vocal cords. 



