making a reverb spring tank

[choklitlove]

i've been "about to" make a ruby amp for a long time now.  i've got another thing now that i want to do with it: i would like to include a stage center reverb inside of the amp.  i would like to make all of this inside of the smallest possible case (i mean really small, 6" or so).  what do you guys think of making a really small reverb tank?  is it possible?  it wouldn't have to sound amazing... it wouldn't be for recording or anything.  if that's not possible, what would be the smallest that could work?

i've seen some stuff on diy tanks, but i can't find them now...   thanks!


EDIT: i found a little.  the electronic peasant has made a couple cool reverbs:

http://www.electronicpeasant.com/projects/springs/springs.html


http://www.electronicpeasant.com/projects/thermio/thermio.html

[petemoore]

what do you guys think of making a really small reverb tank?  is it possible?
  Use what manufacturers supply.
  Accutronics and Hammond have the dimensions of the smallest available reverb tanks.
  I chose a medium dwell unit, it works great.
  If size is critical, a digital Rev. may fit the bill.

[Alex C]

Neat idea; this guy seems to know what he's doing, but I have a question.  I can't tell from the picture or what I read on the site, but is there some sort of insulation or separation between the slinky reverb springs and the circuitry?  The PT has 300V on its secondary, and don't slinkys move?

[Mark Hammer]

Still on the bench in uncompleted form.....

I bought some nice soft, compliant springs from Home Depot or somewhere similar that had about the right compromise between stiffness and compliance when stretched out to around 7-8".  They cost me $1.08@ plus tax.  I soldered one end to the surface of a crystal mic cartridge (though piezo disc would sub nicely) and crazy-glued (cyanoacrylate) the other end to the middle of the voice-coil cap of a small-diameter 8ohm speaker (2-1/2" beeper speakers from computers work nicely).  The speaker is the driver transducer, and the piezo is the pickup end.  Driving the speaker with a low-power power-amp chip like a 386, or feeding it with an op-amp and a 1.5k:8R transformer, produced audible reverb at the other end.

Because you don't want to actually hear the reverb driver, I painted the speaker cone with a mixture of white glue diluted with water such that the cone was stiffened, and then used an X-acto knife to "surgically remove" large sections of speaker cone (leaving the voice-coil area alone) such that the voice coil was still properly suspended and centred, but the cone didn't move quite so much air and would be largely inaudible if placed inside a small aluminum chassis.

While I never got round to finishing and packaging it, it DID work acceptably (given what it cost) in bench tests and could provide a nice little spring reverb unit for a small, portable practice amp (which was the original intention).  Things to keep in mind:

• Springs need to be soft enough to transmit impulses, but not so soft that the next little bit of spring coil won't resonate.  At the same time, they need to be stiff enough to resonate, but not so stiff that they damp vibrations.  The right compromise will be a function of the spring itself and how taughtly it has been stretched.  Some springs that may seem to floppy as is can be perfect if stretched just a little.  Note that even big-name reverb companies use the soldered junction between two springs in series to establish some stiffness in the middle, so that the springs don't sag.  Longer springs always produce lusher reverb with longer decay times, but they introduce risk of sag.  Choose wisely.
• Reverb bandwidth will be a function of the taughtness of the spring.  You can do the experiment easily with two paper cups and string between them and observe the relationship.  Even under optimum circumstances, though, don't expect or encourage maximum bandwidth in the reverb.  Natural reverb sounds like crap when there is no straight signal mixed in.  That's just the way it is.
  Still, make a point of shaping the tone of the driving signal to bring out the best.  Happily, those little beeper speakers have very limited bandwidth themselves, and do some of the bass and treble trimming for you, but you should probably still find ways to goose the content above 1khz a bit at the driver end.
• The more efficiently the signal can be transmitted through the spring, the less the risk of sonic contaminants.  So, if the driver end is electronically efficient, and the receiving end gets a nice hefty "boing" sent to it, then the amount of gain recovery required will be modest, and the risk of introducing hiss along with the reverb will be reduced.  Don't be afraid of pushing the treble hard and then trimming it back a bit.
• Top-notch reverb units often have some limiting built in to suppress the hard transients that can contaminate subsequent signal and introduce interfering modulation.  Remember, that initial hard "sproing" keeps wiggling the spring while you're trying to send subtler signal through.  A simple compressor like the Orange Squeezer could be an excellent candidate for tackling that problem.
• More springs = lusher less specifically resonant sound.  One way to do this is via multiple spring/sensor paths, but a second way is to use a single driver (reducing drive-current requirements) and physically couple secondary springs to the primary one.  This could be in a Y-formation, with 2 secondary springs/sensors, or in a "peace-symbol" formation with three of them.  Since all the secondary springs will have their own little differences in taughtness (that you could exaggerate by adjusting their distance), you can mimic multiple spring paths even though they are all driven by the same common spring.  There is a risk, though, of the weight of multiple secondary springs damping the vibrations of the primary spring. You can get around that by judicious trimming of the primary and secondary springs to keep the pefect balance of length and weight.
• The piezo sensors will require a high input-impedance preamp circuit such as a bifet op-amp or discrete Fet amp.  No big deal, as long as you do it.
• Will it run off a single 9v battery?  Not for long.  Best to use a well-regulated offboard power supply

[choklitlove]

thanks a lot mark.  a lot of what you said is also mentioned in the electronic peasant's explanation, thanks for the detail though.  i'll have to look into what supplies i can get, and see how small i could actually make this thing.  i know it's not finished, but do you have a picture of yours for me to see what you're talking about a little better?  thanks again!

[Snuffy]

If you kicked a reverb tank onstage right before a solo would you sort of explode into the lead?
My buddy told me about kicking reverb tanks and I'm interested

[Nasse]

There was one interesting pic just few days ago in the thread "How about a reverb" or something

I think you can just buy ready made reverb tank and take the parts from there, just cut it shorter

It is quite easy to make a spring that you can use by feeding steel wire on small slowly rotating axle, but getting it clean and neat is not so easy

[darron]

If you kicked a reverb tank onstage right before a solo would you sort of explode into the lead?
My buddy told me about kicking reverb tanks and I'm interested

it makes a horrible sound like an elevator's cords have broken and has fallen 3 stories to the ground!

hahaha. maybe i exaggerated. the oscillations that the transducers send down the springs seems nothing to the force that kicking it gives, and results in a loud clashing noise into your amp.

[Mark Hammer]

Though people here have repeatedly expressed interest in making a spring reverb, there has been surprisingly, and perhaps dismayingly, very little interest over the years in building a plate reverb.  Here's a place to start:

http://www.google.ca/search?client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial_s&hl=en&q=Building+a+plate+reverb&meta=&btnG=Google+Search

The thing to remember about reverberation is that it depends almost entirely on the physics of momentum.  In other words, energy is applied to some body that transmits the energy in a reasonably conserved or efficient manner, such that the energy and the momentum lasts for some period of time.

In fact, that is EXACTLY what happens in a physical space.  Sound is transmitted through the air, and if the walls and other surfaces are highly reflective, the air will provide very little impediment to that acoustic energy continuing its momentum.  That is why walking outside in the falling snow always sounds to intimate and quiet - the snow reduces that momentum and the reverberation comes to a halt.

Plate reverb relies on the omnidirectional (at least in 2-dimensional space) distribution of acoustic energy.  A driver is attached to a flexible, but rigid enough, suspended metal plate (like springs, the suspension is to make sure the vibrations are not damped, so that all momentum is conserved and maximized).  Ideally, or rather traditionally, it is mounted dead center in the plate so that vibrations move outwards from the most flexible part of the plate - a bit like getting more bandwidth from a cymbal by hitting it in just the right spot. 

Unlike a cymbal, where the "rings" are deliberately built into the structure to introduce ring modulation-like textures, the plate is perfectly smooth so that no interference will occur.  Because the plate is a 4-sided geometry (either square or rectangular), the driver is attached at a point which can never really be equidistant from ALL points along the edge (THAT would be the case if the plate was circular, rather than rectangle or square).  This works in the plate's favour because, like a rectangular room, you get different reflections occurring *because* of that different distance-to-the-edge.

One or more contact mics of some sort (piezo, etc.) are placed in the corner/s of the plate, and what it/they sense is the reverberant energy transmitted by the driver through the plate.

Springs vs plates:

• While a single 4-sided plate produces omnidirectional radiation of sound, a spring transmits in one direction only.  In a sense, a plate mimics the use of many sporings of different lengths and tensions.
• Because a spring is coiled, rather than flat, the actual transmission distance covered in a spring is much farther than that of even a fairly large plate.  The "space economy" is the primary reason why springs have been the default option for so many years; decent plate reverbs are like huge gongs, and expensive as a result of their bulk.
• Because springs are "softer", and the transduction process results in some absorption by the spring's softness, bandwidth in a sopring unit tends to be smaller than that of a plate unit.  People often talk about how bright plate units are.  Of course, whether you *want* brightness is another thing.
• There is only one place to stick the transducer on the spring - at the end.  Plates allow for the use of many different concurrent locations of transducers, which can then be mixed in varying proportions to get different sounds.  Just keep in mind that the attachmentment of any transducer is a bit like filling the air with more snowflakes - it tends to dampen the plate and reduce the momentum.

One of the things I have never seen, largely because I haven't looked very hard, is the use of nontraditional plate shapes.  For instance, a pie-shaped plate, with the driver transducer at the pointy end should have an action a bit like a wave pool, where the acoustic energy spreads out, but disappears at the wide end, never to bounce back.  In theory, anyways, that could produe a clearer, less cluttered sound, though clearly working out an appropriate suspension system that would let the plate hang freely (to reduce damping and maximize momentum), without placing too much pressure on any single corner or edge would be a tricky calculation (MUCH easier to do with a square or rectangle!).

In any event, if you have the space and curiosity, don't discount plates.  Plenty of places will sell you sheets of thin guage metal for a reasonable price.  Although things like those high-end EMT units use gold foil, I imagine that one could wring something useful out of a 2' x 4' sheet of flat 24 guage galvanized steel or aluminum.  As for drivers, the traditional driver for homebrew plate units has been those "make-your-wall-into-a-speaker" units that screw in directly to the drywall and use it like a cone.  Sensors can be anything from piezo discs to those suction cup things people use to put on telephone handsets to record conversations.

[LP Hovercraft]

"Journey to the Center of the Mind" by the Amboy Dukes starts with a drop of/kick to a spring reverb tank.  Most likely by Nugent himself.  Great info Mark!  Is there a source out there for the type of transducers one would find on an Accutronics unit?

[zpyder]

If you kicked a reverb tank onstage right before a solo would you sort of explode into the lead?
My buddy told me about kicking reverb tanks and I'm interested

The Doors also did this on stage... and on their recording.  I believe it was the song "and he WALKED ON DOWN THE HALL" "HE PPUT HIS BOOTS ON" and somewhere in the middle of that creepy prose (before he does *something* to his mother) The guitarist picked up and dropped their amp to create a big crashing noise...

Might have the song wrong, but cool effect.  So... yes, if you kick your reverb tank you'll get a big, cacophonous, messy impact-like crashing sound.  Don't know what kind of tunes you play, but it's got a place somewhere...

cheerz
spyder

[Mark Hammer]

Is there a source out there for the type of transducers one would find on an Accutronics unit?

Not that I know of.  The drivers suitable for a plate can be gotten though..

[343 Salty Beans]

If you kicked a reverb tank onstage right before a solo would you sort of explode into the lead?
My buddy told me about kicking reverb tanks and I'm interested

The Doors also did this on stage... and on their recording.  I believe it was the song "and he WALKED ON DOWN THE HALL" "HE PPUT HIS BOOTS ON" and somewhere in the middle of that creepy prose (before he does *something* to his mother) The guitarist picked up and dropped their amp to create a big crashing noise...

Might have the song wrong, but cool effect.  So... yes, if you kick your reverb tank you'll get a big, cacophonous, messy impact-like crashing sound.  Don't know what kind of tunes you play, but it's got a place somewhere...

cheerz
spyder

Actually, my dad has an old peavey amp back when he played keyboard in the 80s with a built-in spring tank. While you carry it, you can hear the spring wobbling and clanking inside. When you knock on the thing hard enough while it's plugged in and on, you get a weird splatty noise.

Listen to the sound sample on digitech's site of their digiverb's 'surf' setting. That weird noise in the background from the attack? It's something like that, but a lot longer and noisier.

digiverb link:

(click on the 'demo' button, you'll need flash and a decent connection)

http://www.digitech.com/products/digiverb.htm

[Mark Hammer]

Folks interested in spring reverb should read this article.

http://img.photobucket.com/albums/v474/mhammer/Reverb1.png
http://img.photobucket.com/albums/v474/mhammer/Reverb2.png

[coffyrock]

In the 50s and 60s, movie gunshot/riccochet sound effects were often created by kicking or otherwise hitting spring reverbs of various types.

On another related subject, I have an organ cabinet called a baldwin panoramic tone cabinet or something, which has huge suspended springs inside to create "some kind" of effect. It looks like the drapy springs in the pic earlier in this thread. I've never used it; I bought it at goodwill for $10 because they thought it was an end table, along with a "matching" baldwin rotary speaker cabinet. The rotary cabinet was $15 because it was not as scratched up.

I don't have an organ to test the panramic tone cabinet, but maybe I'll mod it up for guitar with all this DIY knowledge I'm absorbing from this site!

[idlechatterbox]

I got a small unit that says "Baldwin Panaramic Tone Converter" at a thrift store, for about a dollar, thinking I could make some effect pedal out of it.

If we put our parts together we can make an keyboard/organ!

(I never was able to make heads or tails of the circuitry, hope you have better luck)

[coffyrock]

I haven't looked though, but I'll let you know. I wonder what it does???