What is reverberation?

Each time sound hits a surface a new reflection begins its path within the room, that reflection will hit other surfaces generating other reflections and so quickly filling the space with sound waves.
Remembering that sound propagates through air at quite a fast speed (343 meters per second in standard atmospheric conditions, that is 1235 Kilometres per hour) and that the rooms where we live have dimensions of just a few meters, it is easy to imagine how many reflections will exist in the room at a few hundredths of a second from the sound was generated (think that sounds passes a distance of 4 meters in 11.6 milliseconds, in a 5 x 4 x 3 meter room it hits all the surfaces twice in less than 25 msec). The sum of all these reflected sounds is called reverberation.

This phenomenon is easily perceived by clapping hands in a bare room, it is the sound ‘tail’ that is heard right after the initial clap; it is interesting to note the differences that exist between various kinds of interiors, the most curious are in corridors, stair wells, galleries but even some living room will actually puzzle you.
With this simple experiment you can understand how furniture too can influence the room character: they are always considered in an acoustic correction project, which first aim is to control reverberation.