Introduction: Spring Reverb Experiment With Sugru and LM386s

Picture of Spring Reverb Experiment With Sugru and LM386s
I got some Sugru to play around and wanted to try some stuff.

I like electronics so I thought I could test the material: how well it bonded, if the vibration transfer was sufficient and how much physical stress it could handle. So I had these speakers laying around and it occured to me I could do something with them.
After a couple of tests, the spring reverb was born!

Check a demo video here (we had some focus issues recording, sorry!)

Bear in mind this is still a WORK IN PROGRESS!

This project needs some electronics knowledge and the use of a drill.
I don't intend to teach you how to solder or how to read circuit schematics, I think this site has great resources on those topics already!

Materials you'll need:
===== Main =====
* Two 8 ohm 1/2 watt speakers or similar
* A 5g blister of sugru.
* Slim wire
* A spring. I used a compression spring I had, not sure where it came from.

===== Chassis =====
* Any 1 cm (1/3 inch) thick or so plank of wood of around 1 1/2 the length of the spring.
* Two normal wooden blocks to hold the speakers
* 4x screws, around 2.5 cm long (1 inch)
or anything you want or have around previously made that can support the speakers.
I used a wooden wine box cover as the plank to be able to enclose everything later.

===== Tools =====
* Wire cutter
* A drill to make wholes in the wood. (if needed)
* Screwdriver (if needed)

===== Electronics bill of materials =====
* 9V battery
* 9V battery clip
* 2 female connectors for input or output. Can be TRS or TS, small or big format depending on your taste/use.
* 3x 10kΩ potentiometers
* 2x LM386

Ceramic or polyester capacitors:
* 2x 47nF
* 2x100nF

Electrolitic capacitors:
* 1x 2200μF
* 2x 220μF
* 2x 10μF

Resistors:
* 2x 10Ω
* 1x 47Ω

So let's get started!

Step 1: Prepare the Speakers

Picture of Prepare the Speakers

Open your sugru blister and make two little balls.
Press them against the center of the speaker with moderate force. The center is a circle that's offset forward (relief) from the rest of the speaker. At first it seems it wont stick, but give it a couple of seconds pressing it until it stays. Avoid filling the border with sugru.

Afterwards use something slim, like a toothpick, to make a small hole on the sugru.

You can take your time as sugru is supposed to be malleable for an hour or so.

After you do this step you'll need to wait 24 hours to let sugru completly sit and cure. I left it around 48 just in case.


Step 2: Prepare Speakers for Placement

Picture of Prepare Speakers for Placement

Sorry I haven't taken any pictures while working the wood, but if you ever used a drill it's very easy, just drill two holes on the base and blocks and join them with two screws.

Solder cables to the speakers if they don't have any.

After you have the "chassis", get the speaker, some wire and a calculate a loop around the block of wood that will hold the speaker (and then some). Cut two wires of that length. Repeat the same for the other block if they have different sizes.

Pass them with care on the back of the speaker, trying not to puncture the cloth/paper thing of the speaker.


Step 3: Strapping the Speakers

Picture of Strapping the Speakers

Join the wires behind the block of wood. Make the twists tight so the speaker stays in place.
You can use pliers to help with that, but don't over do it or you might break the wires.

Afterwards bend the remainig wire so you don't cut yourself.

Step 4: (Some Stress Tests)

Picture of (Some Stress Tests)

First I tried the sugru bond with a approximately 250g hammer, waited an hour and it didn't come off.
Then  I tried it with a tense string, and it stretched but after a day it didn't affect the cured sugru much.

Then I did some tests on the spring I was using. It's a pretty hard spring, the hammer didn't even stretched it a bit, only with 1.45kg it actually extended.
This is the spring I'm using on the sugru (and it's tense!) and I haven't found any problems yet (it's been hooked up for several days now)

Step 5: Electronics

Picture of Electronics

Here's the schematic that I'm been using. It's far from complete, I still have some power supply noise I have to take care of and various tweaks, a much missed "dry/wet" mixer, etc.

I'll update the tutorial when I get it right. But this circuit works "well enough" as the video shows.


Step 6: (Bonus: Prepare the Rig for Physical Filtering)

Picture of (Bonus: Prepare the Rig for Physical Filtering)

Originally the idea was to have interchangeable materials between the speakers, not just a spring, to test the filtering and resonance properties of different materials.

I succeeded half-way but had some trouble with the circuit, so I decided to wrap it up and focus on the spring, and maybe afterwards try the generic approach.

Here's how I made it, in case you want to investigate for yourself:

Broken a crocodile cable to get the crocodile tips, collected two small springs from pens' mechanisms, made a loop with a plier and placed them on the holes in the sugru.


Comments

flurng (author)2014-09-26

Excellent work! Although I might suggest a much looser spring ( or you might perhaps just stretch that one. ). Also, for a smoother, more natural sound, try 2 springs, each with a slightly different tension. Otherwise, fantastic!

2bam (author)flurng2014-09-30

Thanks! Nice suggestion!

This is an old project. Eventually the cones (not sugru!) wore off because of the tension, so I guess I found it the hard way why people bolt the spring to the structure and put the speakers/mics on the sides.

Also the circuit is a bit noisy (LM386 can add a lot of noise to the supply line), I fixed that but never got to upload the new schematic (and now I can't find it, classic :p)

I'll keep the spring tip in mind next time

Best regards

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