The Sounds of Speech

Abstract

Note: As professor of vocal physiology, Alexander Graham Bell did pioneer research in “devising methods of exhibiting the vibrations of sounds optically.” In 1873, he became familiar with the phonautograph, developed by Scott and Koenig in 1859, and with the manometric capsule, developed by Koenig in 1862. Greatly impressed by the success of these instruments “to reproduce to the eye those details of sound vibration that produce in our ears the sensation we term timbre, or quality of sound” Bell used an improved form of the phonautograph having a stylus of wood about a foot long. He obtained “large and very beautiful tracings of the vibrations of the air of vowel sounds” upon a smoked glass. In describing his early attempts to improve the methods and apparatus for making speech waves visible and to interpret wave form, Bell wrote: “I then sang the same vowels, in the same way, into the mouth-piece of the manometric capsule, and compared the tracings of the phonautograph with the flame-undulations visible in the mirror. The shapes of the vibrations obtained in the two ways were not exactly identical, and I came to the conclusion that the phonautograph would require considerable modification to be adapted to my purpose. The membrane was loaded by being attached to a long lever, and the bristle, too, at the end of the lever, seemed to have a definite rate of vibration of its own. These facts led me to imagine that the true form of vibration characteristic of the sounds of speech had been distorted in the phonautograph by the instrumentalities employed. I therefore made many experiments to improve the construction of the instrument. I constructed, at home, quite a number of different forms of phonautographs, using membranes of different diameters and thicknesses, and of different materials, and changing the shape of the attached lever and bristle.” Struck by the likeness of the phonautograph and the mechanism of the human ear, Bell conceived the idea of making an instrument modeled after the pattern of the ear, thinking it would probably produce more accurate tracings of speech vibrations. In 1874, he consulted a distinguished aurist, Dr. Clarence Blake of Boston, who suggested that instead of trying to make an instrument modeled after the human ear, the human ear itself be used. Dr. Blake prepared a specimen containing the membrane of tympanum with two bones attached, the malleus and incus. The other bone, the stapes, was removed and a stylus of wheat straw about one inch long was substituted. A sort of speaking tube was arranged to take the place of the outer ear. “When a person sang or spoke to this ear, I was delighted to observe the vibrations of all the parts and the style of hay vibrated with such amplitude as to enable me to obtain tracings of the vibrations on smoked glass.” In the accompanying paper, Dr. I. B. Crandall describes modern methods whereby with the most refined apparatus, highly accurate speech wave forms have been produced. The analysis and interpretation of both vowel and consonant sounds made possible by these records, are the realization of an objective sought by Bell a half century ago. This article is the result of an extended study of 160 graphical records of vowel and consonant sounds, of which a few are reproduced in the present publication. One hundred and four of these records are of vowel sounds and formed the basis of the “Dynamical Study of the Vowel Sounds,” by I. B. Crandall and C. F. Sacia which was published in this Journal in April, 1924. The purpose of the present article is to describe all of the records in sufficient detail, including in one discussion the outstanding characteristics of vowel, semi-vowel and consonant sounds; it is hoped shortly to supplement this with a reproduction of a larger group of records from the complete collection. — Editor.