Plate Reverb

Music, DIY

Winter 2024

The Components

The main components you need for a plate reverb:

• Steel sheet - you want one with a non-rusting surface, like zinc-plated or galvanized. Uncoated steel will rust as it oxidizes. Mine is 24"x30", 26 gauge (0.71mm). Any smaller would probably not be worth the effort.
• Strong frame to hold the sheet (see below)
  
• Hardware to connect the sheet to the frame -  bolts and clevis rod ends
• Transducer speaker
  
• Amplifier to send sound to the transducer
  
• Speaker wire (about 6', you can find it at the local hardware store)
  
• Piezo microphone
  
• Something to provide phantom power, like a mixer or interface. This is only if you are using a mic that requires phantom power. The cheap piezos don't require it, but I don’t recommend using those.
  
• Optional: magnets and some kind of enclosure to attach the speaker + mic to the plate, for easy repositioning. I 3D modeled and 3D printed a couple enclosures for mine, then used CA glue to attach some neodymium magnets to the enclosure.
  
• Optional: adjustable feet to keep the frame from digging into whatever surface it's sitting on. 

The Frame

Barker's unit uses steel angles with mitered and welded corners. This is the first challenge I ran into; the lowest quote I got for making a frame like this was $400. I looked into getting a membership at a local fabrication shop, but the cost would've been similar with the number of classes required. Your local shops may be cheaper. 

So the alternative I found was to use aluminum T-slot extrusions (also know as 80/20 framing). McMaster-Carr, a fantastic mail order company specializing in hardware, will actually cut the extrusions to length and ship them. I used rails that only had slots on two sides. This allowed the face and outer edges of the frame to be solid. The 4 pieces of the frame are connected with L-brackets in the back, screwed with bolts. I chose profiles that were more solid than typical extrusions - I was concerned that the tension on the frame would cause it to buckle if it wasn’t strong enough. I don't have anything to compare this to, but my intuition is telling me I may have over-structured it. This thing is heavy, and I have a feeling the typical profiles would be strong enough for a plate this size.


They're not quite as nice as a welded frame, and you can't magnetize anything to the frame itself the way Barker does with his solenoid percussion, but you can still get a pretty clean look. Extrusions actually provide some advantages over a welded frame, too:

• there are tons of accessories for T-slots, so if you want you can add connections, brackets, build it into a piece of metal furniture, whatever. I got adjustable feet for mine, so it protects whatever surface it's on. The center hole is not threaded, so you'll need a screw tap to create the threads. Luckily, these are also available from McMaster-Carr. Make sure you match the thread size, diameter, etc. when sizing your own.
  
• the frame can be disassembled. Let's say you want to get a bigger plate after you've built this. If you keep one dimension the same (getting a longer rectangle for example), you can reuse 2 of the rails.
  

The most difficult part of actually building this is drilling the holes into the T-slots for the bolts and clevis rod ends. I'd never drilled into metal before; it is tiring, and messy. I used a handheld electric drill. Advice from metalworkers is to drill at a slower RPM which is counterintuitive, but it does work better. Make sure you get a drill bit for metal work. You're going to want to be as precise with these holes as possible, so don't rush it. Use a drill press if you have access to one. 

You can see in the first photo that my plate sits a bit slanted in the frame. I had a near panic attack when I realized the holes I drilled in the frame didn't line up with the ones I made in the plate. It just barely worked in the end, but it required me to drill out more material at some of the holes in the frame. Not fun work. There's a way to avoid this - reference the first set of holes you drill for the next set, rather than whatever your plans say. Here's how I'd do it now:

1. Drill the frame holes first (use your plans). These should be first because it's a lot easier for the drill bit to travel in the T-slot compared to the sheet.
2. Assemble the frame on the ground.
3. Attach the bolts and clevis rod ends to the frame. The bolt heads should be tight to the outer face of the frame
4. Put the plate in the frame. Center it as precisely as possible and mark the locations for holes based on where the rod ends are
5. Drill the holes in the plate. Make sure to use 2 pieces of sacrificial lumber for this, in a sandwich around the plate. If you don't drill through wood that's clamped down, the plate can tear as you drill, leading to a larger hole with sharp edges.

The Electronics

The transducer is a Dayton Audio 4-ohm/20W. 

I started using the cheap piezo mics you find for like $10, but I found the noise floor was so high they were unusable for this purpose. I got a Metal Marshmallow Pro mic that includes a built-in preamp which is much, much better. 

A cheap amplifier from Amazon has been working fine for me. You want one with exposed terminals to attach the speaker wires. An EQ section is a bonus. In fact, using equalizers at different parts of the signal path can be extremely useful in sculpting the sound. 

The Software

There are some limitations if you're trying to do this with a Scarlett 4i4: you won't be able to hear the effect through headphones (only monitors), and you'll have to set up the routing each time you want to use it. This is all I have, so I’ll share what I did to get it working. 

After building this, it actually sat unused for months. I had such a hard time figuring out the software routing! My brain still does not comprehend Focusrite Control, but I've managed to figure out the settings that work. I was aiming for a setup that was always ready to go, but it only takes a minute to route it - not too bad.

If you have the output from your DAW going through output 3 (mono) on the back of the 4i4, your settings would be:

• Temporarily mute Playback 1-2 (Software inputs) under the mix for Line Outputs 3-4 (this prevents feedback).
  
• Mute Playback 3 under the mix for Monitor Outputs 1-2.
  
• Adjust the gain staging. 
  

• As I mentioned, this means you can only hear the reverb through monitors, not headphones, since headphones are married to Line Outputs 3-4 within Focusrite Control. 
  

Examples

Sounds! Below are some examples using the plate. I find I like the effect on drums/percussion more than harmony instruments. The examples are as-is, without any noise clean up applied. 



In the second example I sweep through a high and low EQ on my mixer, after the plate. You can hear the plate oscillate when I turn up the bass frequencies. 




The guitar example with the dry signal mixed in is admittedly pretty subtle. But I think it gives a nice effect. 

Costs

This unfortunately cost way more than I expected, even anticipating it would be more than Barker’s. Here are the rough costs of the materials (Fall 2024):

• $30—steel sheet 24”x30”
• $70—transducer, amp
  
• $100—clevises
  
• $25—socket screw caps
  
• $7—speaker wire
  
• $160—40mm T-slot extrusions, cut to length
  
• $80—flush L-brackets to connect the T-slots together
• $15—antislip leveling feet
• $155—Metal Marshmallow mic
• Total = roughly $650

YMMV of course. Hopefully this helps if you’ve been considering whether or not to build your own plate. 

I've been using the plate algorithm in the Source Audio Collider as my main guitar reverb, so I've known I love the sound of plates. In an effort to get out of the box as much as possible and expand the capabilities of reverb, I decided to make my own plate. I was inspired by Barker's write up on his own plate reverb, which provided a lot of key info. His reported cost of €80 to have the frame fabricated seemed low to me - I anticipated it would be maybe twice that. I'll discuss price later on.  

I want this article to be a guide for anyone else looking to build their own unit. Hopefully you can avoid some of the pitfalls. 

things to note upfront if you want to do this

• Higher CPU usage for exposing more outputs on your interface
  
• This is more useful for playing back recorded sounds than live tracking. Latency and a quirk with the interface I use mean this is a post-effect, not realtime. 
  
• You’ll need a mic preamp with phantom power for the piezo. Two if you want stereo.