Echo

Professional Definition

Sound reflection is a physical phenomenon involving the change of direction of the acoustic wave propagation at the boundary of two media (with different acoustic impedances), as a result of which the wave returns to the medium from which it came. According to the law of reflection, the angle of incidence of the sound beam is equal to the angle of its reflection, provided that the reflecting surface is smooth and large compared to the wavelength.

In acoustical engineering, it is crucial to distinguish between specular reflection (directional), which occurs on flat, hard surfaces, and diffuse reflection, which occurs on irregular structures. The energy of the reflected wave is always less than the energy of the incident wave, as part of the energy is absorbed by the obstacle or transmitted further (penetrates through the partition).

Acoustics in Simple Words

Imagine you are throwing a tennis ball against a wall. If the wall is concrete and smooth, the ball will bounce back to you with great speed – this is hard reflection, typical of concrete, glass, or drywall. Sound behaves similarly here: it hits the obstacle and returns to the room almost with the same force, creating an echo or reverberation noise.

However, if you throw the same ball at a thick blanket hanging on the wall, the ball will lose its momentum and fall to the floor. In acoustics, this corresponds to sound-absorbing materials that minimize reflections. It is also worth thinking about billiards: the cushion of the table is the wall. The angle at which you hit the ball against the cushion is the same as the angle at which it rebounds. When designing concert halls, engineers "play billiards" with sound waves, aiming them so that they reach the listeners' ears rather than circulate aimlessly under the ceiling.

Summary

Sound reflection is a mechanism that can be both an ally and an enemy of good acoustics. Uncontrolled multiple reflections lead to tedious reverberation and sound fluttering. On the other hand, the conscious use of reflective panels (diffusers) allows for a sense of spaciousness and better speech intelligibility without excessive soundproofing of the interior.