Three guys are standing in a row, facing a solid, high wall. Guy A is 10 m from the wall, B is 20 m away from the wall, and C is 30 m away from it. Guy B shouts. Will any other guy be able to hear an echo of Guy B’s shout?

Only guy B and C will be able to hear the echo but guy A  will not be able to hear the echo

Explanation:

Given that:

Guy A  = 10 m away from the wall

Guy B = 20 m away from the wall

Guy C = 30 m away from the wall

At standard Temperature of 20 °C, velocity of sound in dry air ≅ 343 m/s. As such, if there is a reflecting object that produces an echo, it mustn't be more than 17.2 m from where the sound is originating from. As the sound is coming from guy B who is 20 m away, only Guy B and C who are above 17.2 m will only perceive the  echo.

their crystal patterns have been disrupted by stress

its lower due to the doppler effect.: apex