平面波
一种波：在垂直于波传播方向的任一指定平面上，各声学参数（质点位移、密度、压力等）都具有恒定值 —— 即每个声学参数只取决于一个空间坐标，且该坐标轴沿波的传播方向。Kinsler，第 98、107 页
在远离波扰动源的地方，所有的波都将近似变为平面波。 Kinsler，第 98 页
Plane wave
A wave in which each acoustic parameter (particle displacement, density, pressure, etc.) has a constant value on any specified plane that is perpendicular to the direction of wave propagation -- i.e., each acoustic parameter depends only on one spatial coordinate, where the coordinate axis is in the direction of the wave propagation. Kinsler, p. 98, 107
At great distances from the source of a wave disturbance, all waves will become approximately plane. Kinsler, p. 98