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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.
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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.
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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.
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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.
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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.
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27 comments
Sounds great, but is there alot more reverb on the right channel?
Yeah, it may be to do with the glue – one piezo is held by a drop of superglue and the other with a larger glob of heavier, more viscous Ados glue. The superglued one is the louder of the two.
Or it may be an inherent inconsistency in the plate itself – steel is never as uniform as most people assume it to be.
Dude, you got on sine language. Mad props. When will you be signing autographs?
At 3am Wednesday morning, in the old cemetery under Grafton bridge.
Hey Felix, I use double sided sticky tape to mount piezos. Surplustronics has them for a buck each without wires. Its terrific!
I’m going to make one!… that’ll fit in the car.
Oh, and I’ve entered in the monthly comp at DIY stompboxes for delays under 100ms though when you box it up it’s going to be one humongous stompbox!
http://www.diystompboxes.com/smfforum/index.php?topic=76113.40
http://artyone.blogtown.co.nz/
I’ve been meaning to do this and you’ve given me the rquired impetus. Thankyou Felix!
Nice one Sean, I’ve subscribed to your site in great anticipation.
And yeah, double sided tape, of course. Doh!
marvellous web-site…home made electronics-fab! and all done particularly humourously…can’t ask for more than that…
Cheers Andrew!
Hi Felix, you have inspired me to make my own plate reverb. I was wondering how could was the quality of the speaker you used.
Cheers
sorry I meant good instead of could.
Hey Nelson, I used a pretty ordinary 8 inch, 8 ohm speaker from an old home system, probably made in the 70s I think. It’s not exactly the same as the one pictured (I blew that one not long after taking the pics when I turned the amp up really loud and forgot what it was connected to) but similar.
It doesn’t sound like anything special as a speaker, and it’s not particularly powerful. No Idea of the wattage.
As far as I can tell, with this kind of design it doesn’t matter too much. It doesn’t take a lot of sound pressure to vibrate the plate – I’d say finding a good sounding sheet of steel is probably more crucial than finding a good speaker. No thicker than 0.5mm seems to be what most people recommend.
Keep me posted and good luck.
Hello,
I’ve been reading about DIY plate reverbs on the internet for a while and I’d more or less given up on the idea, having no money and not much skill or patience in measuring, etc. I’d read that you have to be pretty precise when it comes to the thickness of the steel, the strength and size of the frame and particularly the tensioning of the plate. …However, having heard your clips, I’m confident that I’d be very happy with something that sounded like yours. It’s absolutely amazing and has all of the characteristics I appreciate in a plate reverb! I HAVE to destroy an old filing cabinet now! Cheers! Tom
Yay, one more reverb and one less filing cabinet – that’s a win/win.
Hi!
I´m currently trying to build my own Plate reverb aswell. Jippie. Your site is really helpfull, Thanks!!
I don´t understand what type of speaker I should use?
I have read on different sites that you should use a piezo speaker a kind of electro magnetic thingy that you kind of glue on the plate? but after listening to you recordings I was amazed.
* I was just worried that having a speaker playing sound wide open towards the plate would leech direct to the Piezo mics.
Is that something you noticed?
* Does the sound in the reverb change alot if you have high or low gain output from the speaker?
Thank you alot in advance!
Kind regards:
//Ted
Hi Ted, happy to help if I can.
In a traditional plate reverb – the fancy expensive ones you might find in a big studio – there is no speaker. The plate is vibrated by a driver (which is kinda like the back bit of a speaker without the cone) and this driver is attached directly to the plate (which kinda turns the whole plate into a giant, flat speaker).
Some people have built home-made plates like this by cutting most of the cone off a speaker and gluing the remaining driver to a plate. I just went one step easier and left the speaker intact, letting it vibrate the plate via the air.
As for the type of speaker, I don’t think it matters too much in this kind of design. All it has to do is vibrate the plate which doesn’t take much power. Just try whatever speakers you have until you find one you like.
The piezos are contact mics, they pick up vibrations in the material they’re attached to but not really in the air around them. This wikipedia page shows exactly what I used.
Good luck and let me know how it goes.
Hi again!
Thank you for your quick answer! My plate reverb is allmost completed. I have a problem with the piezo mics. As soon as I put them on the plate they are humming as hell. doesent matter if I have lots of ducktape between or not. I even bought a cheap guitar mic fully wrapped in rubber that is a piezo aswell just to try, but.. same reult as my own made piezo mic´s
Did you experience this?
I really have no idea what to do??
Thank you again!
Best
/Ted
What sort of wiring are you using to take the signal from the piezo to wherever it goes? Is it just two separate wires (like a speaker cable) or a shielded cable (like a guitar cable)?
If you use shielded cable it shouldn’t be noisy. The shield should be attached to the brass part of the piezo and the signal wire attached to the crystal part.
If you’ve already got it shielded properly and it’s still noisy then there might be something else in your system that isn’t earthed properly. Good luck!
I’m not surprised that you’re having hum problems, especially if you’re running them into a line level (600 ohms – ouch!) input. Piezoelectric elements are ultra high impedance (multi-megohm region). Astatic rates their MC151 crystal element as “equivalent to a 390 pF capacitor.” I’ve had great results both tone and hum wise running piezo’s into an op amp voltage follower (AKA unity gain amplifier). For a cheapie 741, available everywhere for next to nothing, input is pin 3 (noninverting input), output is pin 6 which is shorted to pin 2 (inverting input), locking gain at unity and replacing ALL input power losses, making the input impedance infinity. The 741 requires a split supply, and works best thusly. I use a pair of cheap carbon zinc 9 volt batteries, and replace them every couple years. They’ll last pretty close to their shelf life, and carbon zinc batteries have lower internal noise than alkalines. The 741 will work with as little as +/- 5 volts. I often use “dead” (in most other devices) batteries (And yes I *am* that cheap). Connect the batteries in series. + to pin 7, – to pin 4, and the connection between the two batteries to ground (which is not connected directly to the op amp, just the input and output terminations). I recommend mounting the 741 on (i.e. dead bug) or very near the piezo element to keep the high impedance portion of the cabling to a (ahem) bare minimum. The output impedance is zero, so you can use pretty much any cable you want. I’ve actually used zipcord, with no hum.
And yes this will vastly improve the low frequency response of the piezo’s.
-Mike
Thanks for the tips, Mike. Very helpful.
Everyone said my one should be noisy but it isn’t, so I guess I must’ve done something horribly wrong…
However I’ve been thinking about getting the level up a bit and I’ve got a couple of 741s lying around so I might give that a go.
I don’t think I saw it mentioned explicitly anywhere… what are you using to amplify the piezo elements? Are they just run into a normal mixer/mic pre, or did you build a piezo preamp? (I see mention of how to build one from another commenter, but not what you used in the clips)
I tried building something similar a while ago, but I hot glued the speaker to the plate and the plate itself might have been too thick. Finally, I used crappy dictaphone mic elements removed from their casings and hot glued to the plate… it sounded terrible, LOL, your design is much better.
Hi Scruddles, I was just running them straight into the fx return on my desk, which I guess is line level. That’s how it was working when I made the demo recordings above.
Last week I started building a big case for the unit so I’ve un-wired it all and I’ll probably put it back together with some sort of piezo amp.
Also as I mentioned above, I’ve noticed a big difference with different types of glue – the best seems to be superglue which I think is just because there’s less of it getting between the piezo and the plate, so a better contact. Thicker, more viscous glues seem to reduce the response.
Hey, an old thread but it still going around the world.
http://www.diystompboxes.com/smfforum/index.php?topic=81407.0
I’ve posted a link here at the bottom of page three.
Dear Felix,
Your intuition served you well. Most more expensive diy units i’ve heard sound way too resonant to be usefull.
What steel did you use, what is it’s thickness, overall size & do you think that the extra holes in plate contributed to nice sound?
I really like to know.
Thanks & regards,
david
the netherlands
Hi David, thank you for the compliment.
The steel is the side of a filing cabinet, it measures about 500mm x 1700mm and is about 0.5mm thick.
I too have wondered about the holes but I’m not sure if they have any effect. It seems intuitive that they would, but I don’t know whether the difference is enough to be audible.
It also has a bit of a kink across one corner where it was dropped on the ground, maybe this affects the sound too.
Dear Felix,
Thank you. The 0.5mm plate & not coupling the driver directly, i think; is a nice pad to follow & i will. To cut out the last resonance that is still audible i will try to mix in a bit of anti-phase of each piezo amplifier. In the bx20 of AKG they do that too and it helps a lot. Al tough this reverb unit is imo unusable.
This summer I’ll make the plate reverb.
Good luck & kind regards,
david
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