How do I decide whether a pipe question uses all harmonics or only odd harmonics?
Look at the boundary conditions, not the drawing style.
Look at the boundary conditions, not the drawing style. An open end is a displacement antinode; a closed end is a displacement node. A pipe open at both ends fits an integer number of half-wavelengths and supports n = 1, 2, 3,.... A pipe closed at one end fits odd quarter-wavelengths and supports n = 1, 3, 5,.... Then apply any end correction stated in the question.
Key point
Two open ends: all harmonics; one closed end: odd harmonics only.
Common mistake
using nv/(2L) for every air column.
Memory tip
closed-open means odd quarters.
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