closed tube

A closed tube in acoustics refers to a tube that is open at one end and closed at the other. This configuration creates specific conditions for standing waves to form within the air column. At the closed end, air particles cannot move, resulting in a displacement node. Conversely, at the open end, air particles can move freely, creating a displacement antinode.

The length of a closed tube corresponds to one-quarter of a wavelength. This boundary condition means that only odd harmonics (multiples of the fundamental frequency) can exist as standing waves within the tube. This principle is fundamental to the operation of certain musical instruments, like some types of flutes and organ pipes, where the length of the air column dictates the pitch produced.1