Acoustics & Sound For Musicians - Online Book

The Theory Of Sound Which Constitutes The Physical Basis Of The Art Of Music.

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152               INTERFERENCE OF SOUND. [VII. § 74.
First, suppose that to be from A along the line AB, either through a greater or less distance than AB, back again to A, and so on. Here the separate effects of the two sets of vibrations will be added togetther, the particle will, therefore, perform vibrations of larger extent than it would under either component separately. Next, suppose that, under the second set of vibrations alone, the particle would move from A in the opposite direction to its former course, i.e. along BA produced, shown by a dotted line in the figure. In this case the separate effects are absolutely antagonistic; accordingly the joint result is that due to the difference of its components. The particle will, therefore, execute less extensive vibrations than it would have done under the more powerful of the two components acting alone.
The most striking result presents itself when the two systems of vibrations, besides being in opposition to each other, are also exactly equal in extent. In this case the air-particle, being solicited by equal forces in opposite directions, remains at rest, the two systems of vibrations completely neutralising each other's effects. In general, however, these systems, even when equal in extent of vibration, are neither in complete opposition nor in complete accordance, but in an intermediate attitude, so as only partially to counteract, or support, each other. These conclusions
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E-Book - An Annotated Compendium of Old Time American Songs by James Alverson III