LECTURE II

CHARACTERISTICS OF TONES

ANALYSIS BY THE EAR


Even after the arguments presented, it may seem strange that a single source of sound can emit several distinct tones simultaneously. There is, however, abundant experimental evidence in support of this statement. By listening attentively, one can often distinguish several component tones in the sound from a flute or violin or other instrument.

Helmholtz, who depended mainly upon the ear for the analysis of composite sounds, developed several methods for assisting the ear in the detection of partial tones. (32) He devised the tuned spherical resonator which he used with remarkable success. Fig. 54 shows a series of Helmholtz resonators for the first nineteen overtones of a fundamental having a frequency of 64 vibrations per second; the ten odd-numbered resonators in the series correspond to a fundamental of 128 vibrations per second and its first nine overtones.

The resonator consists of a spherical shell of metal or glass; there is a conical protuberance ending in a small aperture, which is to be inserted in the ear; opposite this aperture is an opening, through which the sound waves influence the air in the resonator. The tuning depends upon the volume of air in the resonator and the size of the opening.

If one ear is stopped while a resonator is applied to the other, most of the tones existing in the surrounding air will be damped or, in effect, excluded, while if a component sound exists which is of the same pitch as that of the resonator, this particular simple tone affects the ear powerfully.

4/19/95.20:48 - 4/19/95.21:53