HANDBOOK OF ACOUSTICS - online book

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

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160
HAND-BOOK OF ACOUSTICS.
Secondly, the time during which a sensation of sound will endure, after its cause has ceased to act, varies for sounds of low and high pitch. For since 16 beats per second in the region of C, coalesce, it is only reasonable to conclude that the sensation of each of these beats remains for -Jg- of a second. Similarly the duration of sound in the region of C| is Jg- of a second, and so on, as given in the last column of the above table. If this conclusion be correct, it seems to afford an explanation of the fact, that the Beating Distance becomes greater as we descend in the scale.
To sum up, then, as far as we have gone: Dissonance between two simple tones, is due to Beats: taking two Simple Tones in unison with one another, and gradually altering the pitch of one of them, the harshness of the dissonance increases with the rapidity of the beats, up to a certain point; beyond that point it diminishes, until finally, all harshness—all dissonance—vanishes when the two tones are at a certain distance apart: and finally, the number of beats per second which produces the greatest dissonance, and the Beating Distance both vary as we ascend and descend in the musical scale.
It would seem from the above, that however much we widen the interval between two simple tones beyond the beating distance, they never again become dissonant, for being now beyond that distance, it is plain they can no longer beat. On putting the matter to the test of experiment, however, it is found that this is not the case ; there are certain intervals, beyond the beating distance, which do beat. For example, if two forks be tuned, one to C, and the other