664 



NATURE 



[January 20, 192 1 



Nature of Vowel Sounds. 

 By Prof. E. W. Scripture. 



11, 



IN a preceding paper (Nature, January 13, 

 p. 632) it was explained that the analysis of 

 vowel curves showed (i) that the fundamental, 

 or voice tone, must consist of a series of puffs, 

 and not of smooth vibrations ; and {2) that the 

 overtones, or the specific vowel tones, must be 

 quite independent of the fundamental — that is, 

 they can just as well be inharmonic as harmonic 

 to it. 



The Manufacture of Vowels. 



For the manufacture of vowels Helmholtz used 

 tuning-forks that gave smooth vibrations and not 

 puffs ; moreover, the only overtones tried were 

 harmonic to the fundamental. Some years ago 

 I made an attempt to manufacture vowels on the 

 principles discovered by the analysis of vowel 

 curves. 



The fundamental was produced by a puff siren 

 (Fig. 7) similar to the familiar one of Seebeck. 



Water 

 Resonator- 



Siren Disc 



Fin. 7. — Puff siren with water resonator. 



As a slit passes across the blast tube a jet of air 

 issues for an instant. This is heard as a faint 

 puff. As the disc is rotated more rapidly' the 

 puffs come oftener, until at one region a low 

 tone appears. With still greater rapidity the 

 pitch of the tone rises. 



When a brass resonator is placed in front of 

 the tube of the siren it sounds loudly when the 

 frequency of the puffs is the same as that of the 

 tone of the resonator, and also less loudly when 

 it is in some other harmonic relation. For in- 

 harmonic relations the resonator is silent. 

 Resonators with hard wells, therefore, cannot be 

 used to produce sounds containing inharmonic 

 icomponents. 



The soft-walled resonators of the mouth can 

 ,be imitated by spreading pieces of meat over wire 

 frames. As this has its inconveniences, a wire 

 frame may be covered with a layer of absorbent 

 cotton soaked in water. Such a resonator is 



NO. 2673, VOL. 106] 



shown in Fig. 7. The walls are quite inelastic. 

 When such a water resonator is placed in front 

 of the tube of the siren, it responds equally well 

 to all tones of the siren, whether harmonic or 

 inharmonic. Two or more resonators can be 

 combined to meet the requirements for various 

 vowels. 



The theory of this vowel siren can be illustrated 

 by the diagrams in Fig. 8. The puifs come as 

 sharp blows almost instantaneous in character ; 

 they are indicated by the crosses. When such 

 a blow strikes a resonator with soft walls, 

 it arouses a vibration in the cavity that dies away 

 very rapidly, as is indicated in the first line of the 

 figure. The vibration is entirely gone before the 

 next puff hits it. The response of the resonator 

 is quite independent of the frequency of the puff. 

 When, however, a puff strikes a resonator with 

 hard walls, it arouses a vibration that dies away 



A_ 



♦ - 



Fig. 8. — Vibrations in a resonator in response to 

 puffs. The puffs are indicated by the crosses. 

 The first line shows the response of a 

 resonator with soft walls. In the second line 

 the puffs hit a resonator with hard waits in 

 such a way as to maintain strong vibrations. 

 In the third line the puffs hit the same resonator 

 in a way to produce little or no effect. 



very slowly. When the next puff comes, the 

 result depends on its relation to the vibration still 

 going on in the cavity. If the puff hits the re- 

 sonator at a moment when its frequency would 

 be a sub-multiple of the frequency of the resonator, 

 then it will reinforce the vibration and make the 

 resonator tone louder. This is illustrated in the 

 second line of the figure. If, on the other hand, 

 it hits the resonator at a moment one-half a period 

 short of a harmonic relation, it will kill the vibra- 

 tion it finds. A very weak tone may be aroused 

 by puffs with a frequency that is not a sub- 

 multiple of the frequency of the resonator, but 

 no strong response can be obtained outside the 

 harmonic relation. 



The siren with water resonators was con- 

 structed with the aid of the Hodgkins fund of 

 the Smithsonian Institution of Washington. 

 It produced most of the typical vowels with sue- 



