Acoustics & Sound For Musicians - Online Book

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

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	120 REFLEXION AT AN OPEN ORIFICE. [V. § 58.
	First, let CABD be a pulse of condensation which has just reached AB. If the pipe had been con­tinuous, the particles of air near AB would have
	moved in the direction of the arrow till they were stopped by the increasing pressure in their front. This would correspond to the instant of greatest density at AB. They would then begin to move in the direction opposite to that of the arrow, the pressure in front i.e., on the left in the figure, being greater than that behind. As, however, the pipe is open and the air free to move in all directions, the condensation just outside its mouth is never great: the particles will move further in the direction of the arrow before being stopped than they would do in the case of a continuous tube and will, therefore, leave behind them a region in which the air is more rarefied than it would have been at the same time in the corresponding part of the continuous tube. This region of rarefied air will produce a pulse of rarefaction which will be transmitted in the direc­tion opposite to that of the arrow. Conversely, when a pulse of rarefaction reaches the open end of the