VOICE AND SPEECH 621 



THE PRODUCTION OF VOICE 



In order to study the changes in the larynx which are associated with 

 voice production we must make use of the laryngoscope. The principle 

 of this instrument is very simple. A large concave mirror with a central 

 aperture is fixed before one eye of the observer, sitting in front of the patient 

 or person to be observed. The latter is directed to throw his head slightly 

 backwards and to open his mouth. In order to keep the tongue out of the 

 way the patient is made to hold the end of it by means of a towel. The 

 mirror is then so arranged as to reflect light from a lamp into the cavity 

 of the mouth. A small mirror fixed in a handle is then warmed, so as to 

 prevent the condensation of the patient's breath, and passed to the back 

 of the mouth until it rests upon and slightly raises the base of the uvula. 

 By this mirror the light reflected into the mouth from the large mirror is 

 again reflected down on to the larynx, and a reflection of the larynx and 

 trachea is seen in the mirror. By laryngoscopic examination we can see 

 the base of the tongue, behind which is the outline of the epiglottis. Behind 

 this again in the middle line are seen the two vocal cords, white and shining 

 (Fig. 312). The cords appear to approximate posteriorly ; between them 

 is a narrow chink, the diameter of which varies with each respiration, being 

 wider during inspiration. On each side of the true vocal cords are seen 

 the pink false vocal cords. In some cases the rings of the trachea, and even 

 the bifurcation of the trachea itself (Fig. 312, c), may be seen in the interval 

 between the vocal cords. 



In order that the vocal cords may be set into vibration, they must be put 

 into a state of tension and the aperture of the glottis narrowed, so as to 

 afford resistance to the current of air. In the dead larynx it is possible 

 to produce sounds by forcing air from bellows through the trachea, after 

 the vocal cords have been put on the stretch by pulling the arytenoid 

 cartilages backwards. By experimenting on patients on whom tracheotomy 

 has been performed, it has been found that the pressure of air in the trachea, . 

 necessary to cause production of voice, is, for a tone of ordinary loudness 

 and pitch, between 140 and 240 mm. of water, and with loud shouting 

 the pressure rises to as much as 945 mm. of water. This pressure is furnished 

 by the contraction of the expiratory muscles, i.e. of the abdomen and of the 

 thorax. Since the pitch of the note produced rises with increasing force 

 of the blast, while the tension of the cords remains constant, it is evident 

 that, in the act of ' swelling ' on a note, the increased pressure necessary 

 for the crescendo must be associated with diminishing tension of the cords. 

 It is the failure to secure this muscular relaxation that so often causes a 

 singer to sing sharp when swelling on any given note. 



The voice, like the sound produced on any musical instrument, may 

 vary either in pitch, loudness, or in quality or timbre. The range of any 

 individual voice is generally about two octaves. The pitch of the voice 

 usually employed is determined chiefly by the length of the vocal cords. 

 Thus in children the voice is high-pitched. Before and at puberty there 



