Historically, there have been two kinds of mechanical reverberation units: Plate and Spring
Reverbs. Plate reverbs are among the most used reverb types in the music industry. The German
company EMT was the first (and still the most important) plate reverb manufacturer. The
EMT 140 Reverberation Unit was their first product. It sounded smoother and more natural
than the spring reverb, and at the same time didn’t demand a dedicated space, like the echo
chamber.
As is implied by the name, plates are metal sheets (usually of relatively large dimensions)
that are hanging in cases, suspended in a way that allows the plate to vibrate well.
The plate is excited by a signal it gets from a transducer, and then vibrates according to
that signal. The vibrations are captured elsewhere in the plate by two contact microphones,
creating a stereo reverberation effect.
The reverberation we get from a plate is not the same as what an acoustic environment
provides, although it sounds closer to natural reverberation than a spring reverb. But it does
add density and ambience to the sound; and that, along with the impracticality of having
a physical “echo chamber”, made plate reverbs the kings of the studio until the advent of
digital reverbs.
There are some other interesting qualities to plate reverbs though. Overall, we can classify
the plate reverb sound as “dense” and “shiny”.