When the source moves at a speed equal to the speed of the wave, a barrier wave is produced in front of the source as each successive wave front piles on top of the previous one.
This regions of constructive interference pattern is a physical reality that must be overcome if the source is to move any faster. 2.1 A barrier wave is formed in front of the source as each successive wave front piles on top of the other.
When a sound wave meets a barrier, some sound is reflected back from the front surface.
In physics, a reflection is when a wave encounters a new medium that acts as a barrier.