<P> The concept of Reverberation Time implicitly supposes that the decay rate of the sound is exponential, so that the sound level diminishes regularly, at a rate of so many dB per second . It is not often the case in real rooms, depending on the disposition of reflective, dispersive and absorbing surfaces . Moreover, successive measurement of the sound level often yields very different results, as differences in phase in the exciting sound build up in notably different sound waves . In 1965, Manfred R. Schroeder published "A new method of Measuring Reverberation Time" in the Journal of the Acoustical Society of America . He proposed to measure, not the power of the sound, but the energy, by integrating it . This made it possible to show the variation in the rate of decay, and to free acousticians from the necessity of averaging many measurements . </P> <P> A performer or a producer of live or recorded music often induces reverberation in a work . Several systems have been developed to produce or to simulate reverberation . </P> <P> The first reverb effects created for recordings used a real physical space as a natural echo chamber . A loudspeaker would play the sound, and then a microphone would pick it up again, including the effects of reverb . Although this is still a common technique, it requires a dedicated soundproofed room, and varying the reverb time is difficult . </P> <P> A plate reverb system uses an electromechanical transducer, similar to the driver in a loudspeaker, to create vibrations in a large plate of sheet metal . The plate's motion is picked up by one or more contact microphones whose output is an audio signal which may be added to the original "dry" signal . In the late 1950s, Elektro - Mess - Technik (EMT) introduced the EMT 140; a 600 - pound (270 kg) model popular in recording studios, contributing to many hit records such as Beatles and Pink Floyd albums recorded at Abbey Road Studios in the 1960s, and others recorded by Bill Porter in Nashville's RCA Studio B. Early units had one pickup for mono output, and later models featured two pickups for stereo use . The reverb time can be adjusted by a damping pad, made from framed acoustic tiles . The closer the damping pad, the shorter the reverb time . However, the pad never touches the plate . Some units also featured a remote control . </P>

An enclosed space for producing reverberation of a sound