Reverberation is the persistence of sound in a particular space after the original sound is produced. A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air. This is most noticeable when the sound source stops but the reflections continue, decreasing in amplitude, until they can no longer be heard. The length of this sound decay, or reverberation time, receives special consideration in the architectural design of large chambers, which need to have specific reverberation times to achieve optimum performance for their intended activity. In comparison to a distinct echo that is 50 to 100 ms after the initial sound, reverberation is many thousands of echoes that arrive in very quick succession (.01 – 1 ms between echoes). As time passes, the volume of the many echoes is reduced until the echoes cannot be heard at all.
Well, back in the day, reverb was primarily created in one of two ways.
Method #1: A spring contraption located within the head of the amplifier would have sound channeled through it, and the sound would reverberate through the spring. A pickup at the end of the spring would channel that fade-out echo into the amp, because as the sound wave traveled it lost intensity, creating that “echo in an empty room” effect. Thus we have spring reverb.
Method #2: The second primary type of reverb is plate reverb, where the sound wave was run through a plate, a small sheet of metal that would reverberate with the sound. In my opinion, this creates a richer, fuller reverb effect. However, because of its cost, the spring reverb became the main type of reverb in vintage amps.
Fast forward to the modern age: digital reverb. The third and most versatile type of reverb. The sound wave of your guitar is fed through algorithms and an echo pattern is created that mirrors, or reproduces, that of a real reverb. There is no actual reverberation occuring within a spring or a plate of metal, it is a purely digital effect. This type of reverberation has opened the door to such reverbs as “hall” and “room” reverb.