Spring Reverb
From WikiRecording
Spring Reverb
A spring reverb is literally what it says it is. It sends the audio signal to one end of the spring by a transducer, that creates waves that travel through the spring, at the other end of the spring there is another transducer that grabs some of the waves and turns it back into an electrical signal and applies it to the dry sound. When a wave arrives at an end of the spring, part of the wave's energy is reflected and stays in the spring. These reflections create the reverb characteristic sound. Sometimes multiple springs of different lengths or characteristics are coupled to produce a more random sound.
Where you'll find one
Hammond Organs, and now mostly used in Guitar Amps, if you have ever picked up or moved an amp while it's on and heard the twangy sound it's most likely the spring reverb getting jostled.
