Reader Robert J. calls this a "really bad" chart (link). The data-ink ratio, he notes, is horrible.
The biggest issue I have are the axes. What is left unsaid is whether the inability to perceive outside the zone of human ability is inconvenient or not. What's missing is a histogram of the stimuli. I'd guess that the distribution is uneven, and there is a concentration inside the humanly perceptible zone. It would be helpful to include what type of stimuli exists at different frequency bands to illustrate what we are missing.
A different comparison that helps interpretation is other mammals. What is the range of perception of dogs, pigs, cows, etc.?
We should also think carefully before putting these two independent quantities onto the same chart. The rectangular region is merely a construct of the chart designer. In fact, the size of the rectangle is arbitrary as the scales on either axis can be made however large we want.