Pro Audio Files

The Basics of Plate Reverb

What is Plate Reverb?

Plate reverb is the broadband resonance generated by vibrating a large metal sheet.

How Plate Reverb Works

EMT140A large metal sheet is suspended with tension springs inside of a housing case. A transducer is placed in the center of this plate; imagine the driver behind your monitor speaker, except instead of it being attached to a rubber cone it is attached to a big sheet of steel. Nearly equidistant from the transducer are two pickups, similar to the pickups on a guitar. These are basically like little microphones. The exact spacing from the transducer, and the exact spacing from the sheet itself will vary depending on the design of the unit. Both the transducer and pickups are powered by an input and output amplifier, respectively.

Signal is fed into the transducer which then reproduces physical vibrations, exactly the same way a speaker works. Except instead of vibrating a cone, the transducer vibrates the metal sheet. And unlike a speaker, which simply moves back and forth to create pressure waves, the metal sheet vibrates in a 360 degree pattern creating transverse waves across its surface.

These waves interact on themselves skewing the frequency response on a micro level. Also, unlike a speaker, the energy created by these vibrations has to dissipate over time. The net result of this is a complex reproduction of the initial sound that decays. To our ears this is fairly similar to how sound acts in a room!

Plate Reverb vs Room Reverb

There are some key sonic differences between a plate and an actual room.

A plate vibrates across a two-dimensional plane, while a room resonates in three dimensions. In the former, the “echo density” is evenly distributed across the entire time the plate is resonating. The timing between pressure waves at the beginning of a plate reverb’s decay is the same as when that decay is tailing off. In a three dimensional room this is not the case. The first set of reflections are fewer and spaced further apart, but as the decay gets later and later the echoes are coming in with greater density. This causes a tonal and textural change that evolves over time in an actual physical space.

Plate reverb is the sound of vibrations through metal, while rooms are the sound of vibrations through air. Sound moves through the metal of a plate anywhere from ten to twenty times faster than it does through the space of a room. This means that not only is the echo density in a plate even throughout its decay, it’s also very very high.

What does that mean in musical terms? Well, imagine the opposite — low echo density is heard as separate reflections, much like the echoes in a delay unit. As density increases, those echoes get closer and closer together. You can imagine a delay unit speeding up from a quarter note, to eighth note, sixteenth note, thirty-second note, sixty-fourth note. Those sixty-fourth note delays start to kind of sound like reverb but with a “ripply” or “ridged” quality. As we speed up from there, the ripples and ridges start to disappear. The faster those echoes appear, or, the higher the echo density, the more smooth and “continuous” the reverb sounds.

Lastly, when sound is propagated through metal, high frequencies actually travel faster than low frequencies. To some extent this happens in all mediums but it is particularly apparent when we are talking about metal. While we hear all of the frequencies of a sound arrive at basically the same time in a room, we hear the high frequencies arrive first and the lower frequencies arrive slightly later in a plate. This is very important when understanding why a plate reverb may be a better or worse choice than a natural space.

Common Uses for Plate Reverb

Now that we understand how a plate reverb works let’s talk about why we might choose the sound of a plate in our music.

Surrealism. Plate reverbs sound similar to actual rooms, but our ear isn’t really fooled. Because of the two dimensional quality, the dispersion effect and the continuous density, our brains can detect that a plate reverb is not an actual physical space. That’s ok! Sometimes we don’t want realism, we want something that sounds peculiar because it teases the mind in a different way.

Coloring. One of my favorite reasons to choose a plate is to color a sound. Because high frequencies arrive to the ear before low frequencies, a psychoacoustic phenomenon known as the precedence effect kicks in. This effect basically means that if we hear bright energy before we hear lower energy, we simply hear everything as being bright. This can make plate reverbs very useful for making a vocal, acoustic guitar, or percussion instruments appear brighter than they actually are. It’s a great way to make our source sound “shiny” without pumping in excess high end.

Blending. The very high and consistent density creates an open character that shapes very well within other reverbs. Take a drum kit for example. In our kit we have the natural room in overheads, and we likely have a room capture as well. The quality of a plate reverb allows us to extend the tail of the snare or toms without creating the effect of a “room within a room”. Plates can also be good for augmenting small room captures to make a room appear slightly bigger.

Plate Reverb Example

Here’s an example of an EMT140 Plate Reverb at work. This is an excerpt from my Mixing With Reverb course that dives deep into the technical aspects and creative uses of reverb.

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Matthew Weiss

Matthew Weiss

Matthew Weiss is a Grammy nominated and Spellemann Award winning audio engineer from Philadelphia. Matthew has mixed songs for Snoop, Sonny Digital, Gorilla Zoe, Uri Caine, Dizzee Rascal, Arrested Development, 9th Wonder, !llmind & more. Get in touch: Weiss-Sound.com.


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