jan 1, 1939 - Spring reverb
Laurens Hammond was granted a patent on a spring-based mechanical reverberation system in 1939. Spring reverb essentially works in the same way as plate reverb, but in a much more compact form, with the transducer and pickup placed at either end of a spring mounted in a small box. Standard spring reverbs have traditionally been particularly popular with guitarists, due to the ease with which they could be built into guitar amps, and prior to the advent of digital reverb, springs were the only way for studio's on a budget to create reverb artificially.
Added to timeline:
Recording Technology in History