Distance to Wall
50 m
Echo Delay
0.29 s
Speed of Sound
343 m/s
Total Distance
100 m
Status
Ready
An echo is a reflected sound wave heard after a delay. Sound travels from a source, strikes a reflective surface, and bounces back to the listener. The time delay depends on the distance to the surface and the speed of sound.
Sound travels at approximately 343 m/s in air at 20°C. The speed increases by about 0.6 m/s for every 1°C rise in temperature. In water sound travels at ~1480 m/s; in steel at ~5000 m/s.
The human ear cannot distinguish two sounds less than 0.1 s apart. For an echo to be heard as separate from the original sound, the reflector must be at least 17 m away (at 20°C).
SONAR (Sound Navigation And Ranging) uses ultrasound pulses and measures the time for the echo to return. Used by submarines, fishing boats, and bats. The distance is calculated from d = v × t ÷ 2.
When many echoes overlap in an enclosed space (e.g. a concert hall), the sound appears to persist — this is reverberation. Unlike a discrete echo, reverb causes the original sound to seem extended.
Medical ultrasound scans, sonar depth-finding, bat echolocation, measuring the depth of the ocean, speed cameras (radar uses the same principle with EM waves), and building acoustics design.