echo distance
Clap two wood blocks together near a solid wall and walk away
from the wall while continuing clapping. When you are about 40
or 50 feet away you will hear an echo.
Sound travels away from the blocks in all directions. The
sound that hits the wall bounces off to travel in a new
direction. You hear the sound as it goes out away from the blocks.
You hear the sound again when the reflected sound reaches you.
When you are close to the wall the two sounds are so close
together that they seem to be a single noise. You only hear
the echo when the two sounds are separated by at least about
1/10 of a second. Since sound travels at about 1120 feet per
second, in 1/10 of a second it will go 112 feet. If you are
56 feet away from the wall the sound will travel 56 feet to the
wall and 56 feet more back to you for a total of 112 feet.