[Telegraphy] needed a reverb for his recording studio. There are hundreds of computer-based and standalone digital reverb systems out there, but he decided to build his own plate reverb. Reverb is an effect used in many professional audio and music recordings. Reverb adds thousands of echos to an audio signal. These echos decrease in amplitude over time. When used correctly, the effect is generally very pleasing to the ear.
A plate reverb uses a plate of sheet metal to generate the reverb. An audio driver is placed in contact with the metal plate. Audio is fed into the driver, which vibrates the plate. The vibrations travel along the surface of the plate, bouncing off the edges and reflecting back. These reflections are captured by a pickup, which then converts them to a voltage signal. The final reverb effect is actually created in the sound engineer’s mixing board when the “dry” source signal is mixed with the signal returned by the plate.
[Telegraphy’s] plate reverb was built almost entirely from found, Radio Shack, and hardware store parts. The plate and frame are from Lowes. The audio driver is a cut up speaker from an old car stereo. The pickup is a modified piezo transducer from Radio Shack. As [Telegraphy] states several times, there are a lot of differing opinions on exactly how and where to mount the various parts of the reverb. Any placement will generate some reverb. The question is where and how to mount things for the best effect. Much like beauty and the eye of the beholder, the answer to that question is in the ear of the listener.
Jump past the break for a tour of a slightly more involved plate reverb at Gallery Acoustics Studio.
“After wiring up the driver into an audio source and running the pickups into a low noise pre-amp”
Would that be a ‘Low-Z’ pre-amp e.g. typical ‘mic’ input?
Piezos need to go into a *very* high-Z / (high impedance) input – otherwise, all the bass is rolled-off & they sound horrible & ‘skreetchy’
– this works well as a buffer pre-amp (& can be knocked up on perfboard in 10 mins):
http://www.till.com/articles/GuitarPreamp/
No, a low noise pre-amp has low self noise when the gain is turned up. You won’t hear buzzing or the hum that you would usually hear when the amp actually begins to amplify the sound of it’s own circuitry. Obviously no amp is noise-less but there are better and worse amps for self noise. Also, Low-Z is typically instrument input not mic input as microphones actually have higher output than most instrument pickups. This varies depending on the microphone (ribbon, condenser, FET, etc.) and the instrument pickup (passive, active, single-coil, humbucker etc.)
Don’t waste your time with the first half of the video. They don’t show anything except the back corner of the plate reverb.
Unless you know, history and theory is important to you – which it is to many :)
And the latter half’s got some TERRIBLE poodle-rock!
Where’s the Arduino?
Opening beers :)
Interesting about the pickup placement. What might be an interesting use, is to stick 2 or more on at different places. Investigate how they sound, then try taking difference signals, modulating them, etc.
You could even try a magnetic pickup from a guitar, or stick a magnet on the plate, and use a simple coil pickup. Maybe alongside the piezo, they’d get different responses which again might be interesting to subtract or multiply.
Lots of interesting stuff to do here, including feedback. I’d have a lot of fun with trying. Unless it turns out nothing good happens, then I’d just be pissed off. But this is the stuff that fascinated musicians in the 60s particularly, getting wierd sounds out of Heath-Robinson studio contraptions.
I don’t think digital is the same, since you have to know what you’re trying to do, before you can program it in. You can’t just move stuff about and plug stuff in randomly, it just doesn’t run.
You could do a digital finite element analysis on a simulated plate, and move the pickups and speaker around, and change springs, material and thickness of the plate, and things like that, until you get a nice sounding result. Once you have that, you can determine impulse response, and make a faster version.
There’s software to do that? Is it meant for music work, or the usual finite element stuff like designing bridges? Is it expensive?
I don’t want to use it. I’m just impressed such stuff exists!
No need to stick a magnet on the plate. As long as the plate is ferrous, you can use a reluctance pickup (i.e., a guitar pickup).
(Come to think of it, does the author ever identify the plate material? To me, it looks like galvanized sheet metal in at least one of the photos…)
Another interesting possiblity would be to sense plate vibration capacitively. Bring a small circular plate/electrode in close proximity to the reverb plate, and apply a DC bias to it (~> 50 VDC). Couple the small plate to a high-impedance preamp through a capacitor (for DC blocking). This is the basic principal behind the the classic condensor microphone, and it would work regardless of whether the reverb plate is ferrous or not..
I think you’re right about the material “they had in stock a 3 ft x 2 ft plated steel sheet metal.”
I used to work at a famous recording studio in Los Angeles. We had our plate reverbs in a small room by itself. One trick we did to attempt to make it sound better was to heat up the room, expanding the metal springs/clips that held the suspended plate before tightening them so that as the room cooled down the metal contracted. Honestly dont know if it helped improve the sound, but fyi…
Later I worked developing digital reverbs using dsp. The secret seemed to be 9 or more all pass filters to smooth out peaks and valleys in the reverb signal.
“Telegraphy needed a reverb for his recording studio.”
You mean “[Telegraphy] needed a reverb for his recording studio.”, don’t you? ;)
OOF! I missed one there – Thanks for the catch, [Dave]! “We” Ninja-edited it in :)
Stupid question probably. Instead of having it attached to the system remotely, could you remove the driver and place it in the actual recording room to get any kind of effect? Or would it just sound like crap? Also I’m assuming he put it in the basement for sound isolation? Either way, neat solution.
I’m not sure, but i don’t think the plates themselves give off that much sound/noise :)
The place would certainly pick up a lot of sound. They are very sensitive and a lot of recording studios back in the day would keep them in the basement so they didn’t pick everything up. What it would sound like, I don’t know, but it would be cool to try!
My experience is that piezos have a rising response so they always come off tinny.
I tried them early in the development of my sustaining guitar. I found that they got fuller response if I had more downbearing, up to a point. Thus the volume and the sustain changed a lot as I used different tunings. So I gave up and went with tried and true contact mic made from gluing on a tiny electret mic under the hollow bridge. I have used these on hammered dulcimer, high end acoustic guitars, etc. Place one on your chest and intro… Dark Side of the Moon.
Glue a couple or 4 or 5 on the sheet for some great sound. Plated not galvanized, the heavy zinc coating or rust would deaden the sound.
Has anyone listened to a can of [Goop] the hand cleaner, it has a boingy reverberant sound when struck on the rim or side. A vat of this kind of gel, driver, pickups in 3D???
Actually I have noticed that feel to the gel. As a teenager washing dishes, etc I noticed a lot of things
that changed with fluids and stuff ( many years before the “Stomp” shows came along )
I’ve read that the Star Wars laser sounds were guy wires pinged.
put your ear on any flagpole and listen….so many things out there.
I could also tell how some foods were cooking or setting by the sound.
slap and hold your hand on the end of a tube and listen to the tone,
now try it with a sharp slap and bounce..
notice the halving or doubling of frequency with the clap hold or bounce.
ADD can interesting & useful sometimes.