Loudness.—Loudness, which is the sensory relation to the physical property of intensity, depends on the energy in its various component partials. The rate of energy output in the case of an ordinary voice is extremely small, being about 125 ergs per second, i.e., less than a fiftieth of a millionth of a horse-power. Loudness is a function of pitch and the amplitude of the move ments of the vocal cords. If the response of the ear were of a linear character, the intensity of the auditory impressions would be proportional to the square of the product of the amplitude and pitch, to which the term "physiological intensity" has been applied. But at intensities considerably above minimum audibility, there is no proportionality between sound pressure and aural response, for effects are produced in the ear which are not present in the voice which excites them. This degree of non-linearity varies with dif ferent persons. Moreover there occurs a masking of one tone by another. A loud tone of low pitch can obscure a weak high tone, but an intense high tone has but little masking effect on low ones.
Methods of Investigation.—Among the methods and appar atus for investigating the attributes of voice, the following may be mentioned. For duration and pitch, a phonetic kymograph with tambours and an electrically-driven tuning fork of 1 oo– are the instruments generally employed. Relative loudness can also be in vestigated by these, although electric methods of measuring the energy output are far more effective.
For the investigation of quality, methods may be classified under three heads according to the apparatus employed. (a) Those using resonators for picking out the component partials. Helm holtz (1862) determined the maximal response (subjectively) by the ear. Konig (1868) employing his manometric flames in con junction with resonators, showed the response objectively. Reso nators in conjunction with a hot-wire microphone have been em ployed by Tucker and Paris (1921). Garten (1921) used a var iable resonator where maximal response was registered on a soap film recorder. Stumpf (1922) used tuning forks as resonators. (b) Those depending on subjective observations on the changes of quality which the voice undergoes when certain tones are elimin ated. Stumpf employed interference tubes, while Fletcher, Cran dall, Wegel, and others, have used the electric wave filter invented by Dr. Campbell for cutting out frequencies. (c) For objective measurements of quality, curve-tracings or oscillograms of air vibrations produced by the voice are obtained. They are then sub mitted to harmonic analysis to obtain the component partials. Several instruments have been devised. Those used by the Bell Telephone Laboratories and research laboratories of the American Telephone Company in their magnificent work on speech should be first mentioned. F. Trendelenburg used the "condenser micro phone" of Riegger. Miller in his "phonodeik" used a glass mem brane. The "cathode-ray oscillograph" and "Hilger's audiometer" should also be mentioned. Hermann and Scripture in their re searches enlarged the curves of phonograph and gramophone records.
"Sonance."—The beauty of the voice is mainly determined by its quality, but there is another condition which influences the artistic effectiveness of it. Metfessel, of the University of Iowa,
has examined minutely records of songs sung by some famous singers, and has found in every case a certain periodic departure from true pitch, accompanied by a periodic change in amplitude. There is every reason to suppose that much of the aesthetic value of a great singer's voice is attributable to these fluctuations, on the principle that art consists of rhythmic deviations from regularity. To the perceptive fusion of the successive changes in tone-attrib utes, Metfessel has given the name "sonance." Popular apprecia tion of voice-quality in singers, denoted by the term "quality," is as Metfessel states, a combination of "quality or timbre" and "son ance" although the two things should not be confused.
Substitutes for the Larynx.—Laryngectomized subjects have been known to develop a capacity for producing sounds which in essentials resemble normal voice. Burger and Kaiser of Amster dam report a case where a pseudo-larynx has been developed in the oesophagus. The vicarious lung was the stomach, and the lips of the pseudo-glottis were actuated by ejecting air which had previously been swallowed. It is reported that the subject could sing, speak and use the telephone. Indeed, vocally, he carried on like a normal person.
Attempts have also been made with more or less success to supply the voice element in speech by means of vibrating reeds of rubber or thin metal. The best known of these devices is the "MacKenty-Western Electric Artificial Larynx." By using it the subject is able to direct the expiratory current on to a rubber reed when voicing is required.