Can you explain in a few words how the echo is generated?

Echo is a common sound phenomenon in our daily life. During the propagation process, sound waves will be reflected at the interface when they encounter large reflecting surfaces (such as the walls of buildings, etc.), and people will be able to interact with them. The reflected sound wave separated from the original sound is called echo. The condition for the human ear to distinguish the echo is that the reflected sound has sufficient sound intensity, and the time difference with the original sound must be greater than 0.1s. When the size of the reflecting surface is much larger than the wavelength of the incident sound, The echo you hear is the clearest. Sound propagates along a straight line in a uniform medium. When sound encounters a larger obstacle during propagation, it will be reflected by the interface of the obstacle, and the reflected sound is called echo.

As long as there are obstacles, there will be echo. In some cases, the echo phenomenon is not obvious, but it cannot be mistaken for the absence of echo. The human ear can only distinguish two sounds that are separated by more than 0.1s. If the obstacle is different from The distance between the sound emitters is relatively close, and the distance between the original sound and the echo is less than 0.1s. The echo will be mixed with the original sound, making it difficult for people to detect. If the sound speed is 340m/s, the human ear needs to distinguish the original sound from the echo. The distance to the obstacle must be at least 17m to distinguish the echo from the original sound, so that you can have the feeling of hearing the sound twice.