an ultrasound
I would guess that there is no SIGNIFICANT amount of echo, because they were designed that way on purpose. The way this can be done is by covering walls and floors with materials that absorb most sound.
No. Nothing can travel faster than light.
we hear an echo because its in our blood to hear things in a repeditive form but a lot quieter.
Ultrasonography
Echoes of sound and images in a mirror involves sound waves and light waves respectively being reflected off a surface.
sonar
it measures the depth under water
hard and smooth surfaces will produce the best echoes.
sonar
This sounds like it's probably the sonar system of a submarine.
The Echoes was created in 1959.
Echoes of Refuge was created in 2006.
Echoes of Honor was created in 1998.
Eternal Echoes was created in 2001.
Echoes from the Ocean was created in 1999.
Imperial Echoes was created in 1928.
Echoes of Eternity was created in 2005.