DYNAMICAL STUDY OF THE VOWEL SOUNDS 115 



Attempts were also made at models for long a and short I, using the 

 theoretical data. These seemed to give whispered sounds which sug- 

 gested the true ones, but were not very satisfactory when excited by the 

 artificial larynx. It is evidently more difficult to imitate the mouth 

 structure by such simple means, when the outer conductivity {Ki, the 

 orifice between lips and teeth) is small, and the inner orifice K^ is large. 

 And in addition it is likely that the artificial larynx does not supply 

 sufiicient high frequency energy to excite these sounds properly. 

 There is also, of course, the difficulty of applying the simple resonator 

 theory, when the conductivity of an orifice is comparable to one of the 

 dimensions of the adjacent volume. 



Conclusion 



In this paper we have attempted to visualize the mechanism of the 

 vowel sounds, on the basis of previous work, certain simple calcula- 

 tions, and a few rough experiments. It appears that the vowel sounds 

 are usually produced by a double resonator system whose behavior in 

 itself is thoroughly understood; but this does not by any means close 

 the subject. A most interesting field of study remains in the excita- 

 tion of the resonator system, to say nothing of the various factors which 

 produce damping in the system itself. 



We know from laboratory experiments that a reed (or a simple 

 "squawker" made of rubber strip) is by itself a very poor imitation of 

 the vocal cord apparatus. The artificial larynx, for example, will not 

 vibrate properly unless a tube some 15 inches long is interposed be- 

 tween the "larynx" and the pressure reservoir by which it is blown. 

 Correspondingly, we should expect the wind-pipe leading from the 

 lungs to the human larynx to have a very important role in fixing the 

 lower frequencies produced by the vocal cord apparatus. The me- 

 chanical problem indicated for study in this connection is the excitation 

 of a reed-pipe with the reed at the distant end of the pipe, an inversion 

 of the arrangement of ordinary wind instruments. 



Consider the question of damping. In the apparatus used by J. 

 Q. Stewart ^^' (tuned electrical circuits excited by an interrupter) the 

 damping could be systematically adjusted; this is the only case I 

 know of, in experimenting with speech sounds, in which this adjust- 

 ment was possible. In ordinary mechanical apparatus damping is 

 difficult to control. Yet, damping is a significant element in the char- 

 acter of the constituent vibrations of either sustained or transient 

 vowel sounds. For example, I have already pointed out ^^ the close 



^^ Nature, Sept. 2, 1922. "An Electrical Analogue of the Vocal Organs." 

 " "The Sounds of Speech," end of § V. Refer also to Records and Fig. 14 of that 

 paper. 



