Reverberation consists of many reflections of a sound, maintaining the overall sound in a room for a time even after the direct sound has stopped.
Reverberation can cause problems in many types of building, particularly those with large, relatively empty spaces. Restaurants, bars, school halls, foyers, atriums, auditoriums and open-plan offices are all examples of spaces that commonly experience this issue.
Hard, reflective surfaces, such as glass, wood, metal and stone, cause sound to reverberate more. In a room with more acoustically reflective surfaces, it will take longer for the sound to die away, leaving the listener struggling with poor speech clarity.
The reverberant characteristic of a room is defined by the Reverberation Time RT60 which is the time it takes for the sound pressure level Lp (SPL) to decrease by 60 dB.
The optimum reverberation time depends on the size of the room and its activity. For classrooms and offices it can vary between 0.6 seconds and 1.3 seconds and for larger spaces such as concert and event halls it could be over 2 seconds.
In order to obtain the desired reverberation time sound absorbent materials are introduced onto the hard reflective surfaces. Depending on the amount used the reverberation time can be reduced to suit the room size and relevant activity.