The human ear cannot distinguish echo from the original direct sound if the delay is less than 1/10 of a second. This illustration depicts the principle of sediment echo sounding, which uses a narrow beam of high energy and low frequency When sound, or the echo itself, is reflected multiple times from multiple surfaces, the echo is characterized as a reverberation. This can be heard when the reflection returns with sufficient magnitude and delay to be perceived distinctly. The reason of reflection may be explained as a discontinuity in the propagation medium. Echoes are also the basis of Sonar technology.Īcoustic waves are reflected by walls or other hard surfaces, such as mountains and privacy fences. Some animals use echo for location sensing and navigation, such as cetaceans (dolphins and whales) and bats in a process known as echolocation. Echo in the Greek folk story is a mountain nymph whose ability to speak was cursed, leaving her able only to repeat the last words spoken to her. The word echo derives from the Greek ἠχώ ( ēchō), itself from ἦχος ( ēchos), 'sound'. A true echo is a single reflection of the sound source. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room. The delay is directly proportional to the distance of the reflecting surface from the source and the listener. In audio signal processing and acoustics, an echo is a reflection of sound that arrives at the listener with a delay after the direct sound.

Reflection of sound delayed after direct sound as heard by listener

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