HANDBOOK OF ACOUSTICS - online book

A complete view of Acoustical Science & its bearings on music, for musicians & music students.

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76
HAND-BOOK OF ACOUSTICS.
pure, the second and third being accompanied by characteristic noises, and the fourth having its peculiar variation of intensity; but they all agree in being gentle and somewhat dull. Moreover, they can be strictly compared in their own class ; thus, for example, the tones from tuning-forks are all alike in quality; in selecting a tuning-fork, no one ever thinks of the quality of its tone.
There are two methods, by which the important proposition now under consideration may be proved,—the analytical, and the synthetical. The process in the former case is to take two sounds, which differ in quality, and by analysing them into their constituent partials (with or without the aid of resonators), show that these latter differ in the two cases, either in number, order, or in their relative intensities. Thus, if the student analyses a tone of rich and full quality, he will find the first six partials tolerably well developed, while on the other hand, in a tone of poor or thin quality, he will find most of them absent, or of much less intensity. Again, the metallic or brassy quality (as it is termed) of instruments of the trumpet class, he will find to be due to the clashing of very high partials, which are very prominent in such instruments, and which, as will be seen by referring to the table on page 72, he very close together. As another illustration, the peculiar quality of the tones of the clarionet, may be accounted for, by the fact, that only the odd partials, the 1st, 3rd,, &c, will be found to be present in the tones of this instrument. The student will find, in the analysis of the vowel sounds, a very instructive series of experi­ments. The differences in these sounds, must be simply differences in quality, according to our definition; and thus if the proposition under discussion be true, we ought to find corresponding differences in the number, order, or relative intensities of the partials present in the vowel sounds. On trial, this will be found to be the case. If, for example, the "a" as in "father" be sounded by a good voice, all the first six partials may be easily heard; but if the same voice gives the " oo " sound, scarcely anything but the fundamental will be detected.
The general process, in the synthetical method of proof, is, to take simple tones of the relative pitch of the series of partials, and, by combining these together in different numbers and orders, and with different intensities produce different qualities of tone. The first difficulty here, is to procure perfectly simple tones. These are best obtained from tuning-forks fitted with suitable resonatingboxes. An elementary experiment can be conducted as follows. Select two