Acoustics & Sound For Musicians - Online Book

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

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60                     RESONANT AIR-COLUMNS.         [III. §40.
and there reflected. When this rarefaction returns to A, the free end of the spring will momentarily resume the position within the mouth of the pipe to which it was originally pushed. The elasticity of the spring thus causes it to lengthen and shut. as a whole in consequence of the single push origi­nally given it, and this motion would for a time continue, its successive periods being four times the space of time occupied by a pulse of condensation or rarefaction in traversing the length of the pipe. The free end of the spring may, however, be pushed and pulled alternately so as to reinforce each pulse as it arrives at the mouth of the pipe, and in this manner the maximum of motion will be com­municated to the spring. In this case, one outward and one inward impulse must be communicated to the free end of the spring during the time which elapses while a pulse traverses four times the length of the pipe. Reverting to the actual conditions of our problem, we have the resonance of the air-column in place of the alternate lengthening and shortening of the spring. The to-and-fro im­pulses at A are impressed by a vibrating fork. The Sound-pulse traverses four times the length of the pipe while the fork is performing one complete vibra­tion. We know, however [§ 15 p. 32], that during this latter period the Sound-pulse produced by the
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E-Book - An Annotated Compendium of Old Time American Songs by James Alverson III