Why are echoes heard by listeners?

Echoes are heard by listeners primarily because the reflected sound reaches the ear after a slight delay. This phenomenon occurs when sound waves bounce off surfaces, such as buildings, mountains, or large walls, and travel back to the listener. The time taken for these sound waves to return is what creates the perception of an echo. For an echo to be perceived distinctly, the delay between the original sound and the reflected sound must be at least 0.1 seconds; otherwise, the listener may not be able to differentiate between the original sound and its reflection.

In contrast, amplifying the original sound would not specifically account for the phenomenon of echoes, as echoes are about the timing of sound reflections rather than their intensity. The creation of new sound waves is not what constitutes an echo; rather, it's the original sound's reflection. Finally, dissonant frequencies pertain to the quality of sound harmony and do not relate to the mechanics of echo production, which relies on timing rather than frequency relationships. Thus, the key reason listeners experience echoes is due to the arrival of reflected sound waves after a slight delay, allowing them to discern the distinction from the initial sound.