Open Pipes, Stopped Pipes and Double Stopped Pipes
John Bellamy Taylor · The Journal of the Acoustical Society of America · 1931
Air columns in rigid tubes reflect pulses (sound waves) at the ends. The classical sounding or vibrating air column is the organ pipe, broadly classed as either “open” or “stopped” and giving tones of different quality because lack of symmetry in stopped organ pipes suppresses the evenly numbered harmonic overtones. Pipes of both classes are usually considered to be so rigid that all of the “output” to free air occurs at two ends of open pipe or at single opening (mouth) of the stopped pipes. This rigidity assumption may not be justified. If a pipe is stopped at both ends, symmetry is restored with opportunity for vibrations in the complete harmonic series. But with no free vent to outer air the double stopped pipes obviously may not be energized by the usual form of air stream; also confined vibrations will not be heard outside. These seemingly unworkable conditions are met by supplying energy and also withdrawing sound output at nodal points, rather than at loops (ventral segments). Such abstraction of energy at node of vibrating air column is useful in cases where the tone or vibration is to be transferred to a denser medium, e.g., to a liquid or to a solid such as a sounding board.