What is the minimum distance required between a source of sound and an obstacle to hear a distinct echo under normal conditions?

💡 Solution & Explanation

For an echo to be distinctly heard by the human ear, the minimum distance between the sound source and the reflecting obstacle must be 17.2 meters, given that the speed of sound in air is approximately 344 meters per second and persistence of hearing is one-tenth of a second. Shorter distances cause the reflected sound to merge with the original sound as reverberation.