Reverb - what is it and how to fight it?

Theoretically, reverberation is the gradual fading of sound energy after the sound source has ceased, caused by reflections of sound waves in an enclosed space, i.e., from the surfaces of walls, floor, ceiling, and objects present in the room. The human ear perceives reverberation as a sound that lasts for a certain period, which results in its amplification. Why does this happen? In an open space, such as on the street, sound fades with distance (by 6 dB with each doubling of distance). In a closed room, however, this sound is reflected multiple times from all flat surfaces and returns to us. The more sound reflections there are, the greater the reverberation in the room.

Therefore, it is important to remember that in closed rooms, both direct sound waves and waves reflected from all surfaces reach our ears. They arrive with varying time delays, depending on the distance between our ears and the reflecting surface and the sound source. This phenomenon is similar to the so-called echo, but here we clearly hear the difference between direct and reflected sound. In contrast, with reverberation, all waves (direct and reflected) blend into a single prolonged sound.

When there is a large reverberation in a room, sound fades very slowly. This creates what is known as reverberation noise. This means that a significant amount of the sound reaching our ears is reflected rather than direct sound. Sometimes, reverberation is desirable under controlled conditions. For example, in a lecture hall, the speaker's voice should be audible from a great distance, even in the last rows. In such cases, a certain amount of reflections and natural amplification of sound is desirable. However, the problem arises when there are too many sound reflections, and they do not propagate evenly throughout the room. This makes the lecturer's voice unclear, sharp, or tiring. In small rooms such as focus rooms, small and medium conference rooms, or classrooms, a low level of reverberation is required. This results in very high speech intelligibility, with sound being precise and pleasant to hear.

Reverberation in a room is measured using the so-called reverberation time (Reverberation Time – RT). This is a fundamental parameter in architectural acoustics. It defines the time it takes for sound to fade in a given room. For instance, the reverberation time T60 is the period from the moment the sound source is interrupted until the sound level decreases by 60 dB, measured in seconds (s). Reverberation time depends on many factors such as: – the volume of the room (generally the larger, the longer the reverberation time) – the shape and proportions of the room (parallel walls, flat surfaces) – the amount of hard, reflecting surfaces (windows, bare walls, tiles, stone, metal) – the amount of sound-absorbing materials (acoustic ceilings, wall panels, carpeting) – the number of sound-dispersing elements (furniture, grid ceilings, acoustic screens)