Putting natural reverb aside (mic recording ambiance in a space) most of the classic tracks of the 1960s onwards used plate and spring reverbs.
A plate reverb was a solid construction of a sheet of metal that was suspended within an enclosure and held together by springs or clamps and only at the corners. The idea being that the sheet is allowed to vibrate. A transducer, much like a speaker driver, was used to direct energy and generate vibrations. These vibrations were then picked up by mics (microphones), or pickup transducers, attached to specific parts of the sheet (plate). In the early days a single mic was used for mono and later 2 mics were used for stereo. A damping pad would be used to adjust reverb time, the closer the pad the shorter the reverb time.
These reverbs were big (1 meter square and above for the sheets) and had to be constructed into a solid sound proofed framework. The reflections travel faster and build up quicker due to the shape and construction of the sheet and therefore exhibit a denser and brighter sound that has become synonymous with plates. There is so much energy created by the nature of the sheet process that the early reflections are so dense that they are almost inaudible, or rather indistinguishable, and because the decay is long and smooth (the sheet denotes the time variances here) they are very specific in the type of ‘colour’ they impart onto the dry signal. A physical metal sheet will always allow sound to travel faster than if it were travelling through air and this accounted for one of its unique qualities: reflections.
The construction of such a device is not easy. Although the actual construction only requires some elbow grease it is the construction and ‘calibration’ of the sheet (thickness, tension mounting etc) that is complex. ‘Taming’ the sheet is another issue as metal that vibrates can ‘ring’. However, nowadays we are spoilt for choice with the multitude of reverb plate presets in software reverbs. But, as in most cases, they are only emulations and only a few truly capture the sound of this very specific type of reverb.
Excerpt taken from Creative Effects book.