Standing-wave modes require one boundary per spatial dimension.

Evidence

1 boundary x = 1 2 boundaries x = 1, y = 1 3 boundaries x = 1, y = 1, z = 1 FIGURE 6. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2144

Categorization

• DEFINE: Defines the boundary condition per mode in one, two, and three dimensions; too fragmentary to stand as prose but notes the axis-per-dimension rule.