Boundary-induced source power changes scale with distance relative to wavelength

Evidence

Note that in these graphs, the x-axis is the number of wavelengths with respect to the distance x from the boundary. This is analogous to frequency but scaled as with respect to distance. Thus if x equaled 1 meter, a value of 1 on the x-axis would correspond to a wavelength of 1 meter (344 Hz); if x equaled half a meter, a value of 1 on the x-axis would correspond to a wavelength of half a meter (688 Hz), and so on. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2134