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ON THE QUALITY OF MUSICAL SOUNDS. 73
pound, and that the partials of which these compound tones consist, belong to the series given above; that is to say, though any one or more of these partials may be absent, no sound of any other pitch, than those given above, ever makes its appearance.
Instruments which produce only simple tones are comparatively rare. A tuning-fork, when struck on a hard substance, or when carelessly bowed, gives a compound tone, consisting of a funda­mental and one or two very high overtones. When, however, it is mounted on a resonance box of proper dimensions and carefully bowed, the fundamental tone is so strengthened by resonance, that the resulting sound is practically free from overtones. The tones of flutes and of wide stopped organ pipes gently blown, and the highest notes of the piano, are nearly simple.
The relative intensities of the partials forming a compound tone vary very greatly in different instruments, and even in different parts of the same instrument; thus, on the lower part of a piano, the third partial is generally louder than the fundamental, while on the upper part, it is very much softer. In some voices, again, and with some vowel sounds, the third partial is painfully prominent, while in other voices and with other vowel sounds, it is only detected with difficulty. As a general rule, the farther the partial is from the fundamental, the less is its intensity. Taking the sound from a well-bowed violin as a model of tone, Helmholtz has given the following approximation to the relative intensities of its partials, the intensity of the fundamental being taken as 1.
Considering the loudness of the partials in many instruments, it may be a matter of surprise to some, that they are not more easily recognised. It should be remembered, however, that, as the partials of a compound tone all begin together, and usually continue with unvarying relative intensities till the tone ends, when they all