The results of an experimental study of a relatively unfamiliar mode of propagation are presented: the zero‐order mode in a tube with massive wall reactance. The observed and theoretical disperison curves, which show good agreement, display a high‐pass cut‐off frequency. There is a dead zone between this frequency and the ring resonant frequency of the tube.

The phase velocities c2 are measured indirectly from the directivity patterns of a receiver in the form of a long rubber hose coupled to a microphone; these patterns are characterized by two symmetrical lobes whose angular separation is 2 cos−1c/c2, c being the sound velocity.

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