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Today it stopped raining for long enough for me to do something I’ve been wanting to do for a while – build a stereo plate reverb unit. It took a couple of hours, was made mostly from stuff I found at the tip, cost about $10 and it sounds awesome. If you want to make one of these you can do so with some very basic tools, parts and skills.

The horizontal wires are unrelated. More pics below.

if you’re unfamiliar with how a plate reverb works:

It’s a matter of sending an audio signal to some type of transducer (in this case a speaker) which vibrates a piece of sheet metal (the plate). The vibrations travel though the plate as waves – like ripples from a pebble dropped in a pond – from the speaker at the centre to the edges where they’re picked up by another transducer (in this case 2 piezo buzzers). These convert the wave – it’s shape now altered by the plate – back into an electrical signal and return it as reverb to be blended with the original sound.

Yeah, you can simulate this digitally but analogue plate reverbs have their own special qualities, and if you make your own you’ll be able to create totally unique reverb sounds which are all yours.

As far as I know these type of reverbs were first widely used in the 60s and were considered to be a vast improvement on the earlier “spring” reverbs, the boingy sounding ones that you mostly find these days in Fender-type guitar amps, the ones that make those great clanging noises when you kick them. Don’t kick your amp.

Plate reverbs on the other hand create the rich, dense type of reverb we hear on records by The Beach Boys, The Beatles, Phil Spector, anything from Motown etc etc.

my one sounds like this:

Ok Lani isn’t going to be happy about this, but unfortunately for her this clip is just perfect for demonstrating reverb.

Here’s the dry voice:

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and with the magnificent plate reverb:

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Here’s a dry guitar track:

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and with glorious stereo plate reverb:

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the parts i’ve used are

• An old steel bed frame (could just as easily be built from wood)
• The side of a filing cabinet for the plate
• Some small springs from another old bed
• A speaker
• Piezo transducers (1 for mono, 2 for stereo)
• Some light steel wire
• Some speaker wire
• Some shielded audio cable
• Some glue

tools

I used a drill and a pair of pliers. In a pinch you could do it without the drill. Or the pliers.

Oh yeah, you’ll probably need some sort of amp to drive the signal to the speaker. I’m just using my bass head at the moment but I’ll sort out a dedicated amp sometime. Probably.

The shack I live in is pretty tight so for now the unit is hanging up on the porch. The plate is attached to the frame by springs at either end. I haven’t tried adjusting the tension on the plate or the placement of the springs yet, this is just as it happened to go together.

The speaker is an old New Zealand made Plessey, suspended on wires (to keep the weight down) and positioned at roughly the centre of the plate.

As you can see, the front of the speaker cone is about 10mm – 15mm from the surface of the plate. This is just where it happened to land but it seems to work pretty well.

The piezo transducers are glued to the plate at each end – one for the left channel and one for the right. It sounds great in mono too but if you have a stereo return or a couple of spare channels you might as well give yourself the option.

what now?

• I’ll definitely experiment with the tension of the plate, I think that could have quite a dramatic effect on the colour of the reverb. At the moment it’s quite dark which is nice for some things.
• I might play around with the speaker placement, although I’m pretty happy with how it’s working the plate.
• The piezos only cost a few dollars each so I might try some more in various places around the plate. I think the distance from the centre should relate to the length of the reverb but I’m not sure about that. With more piezos perhaps I could run several different sounding signals to a small mixer and play with them a bit before sending them to the desk.
• Oh, and I want to build a box for it to live in or find somewhere quiet to hang it. It’s fairly sensitive to wind and dogs.

Any other ideas? Have any advice or questions about building these things? Let me know in the comments.

UPDATE:

I’ve now built a mixer for mixing four reverb returns. Read about it here.