I’ve been experimenting with similar designs, but this is the best sounding so far. The idea is to amplify a signal (in this case using a $1 aliexpress amplifier module) and feed it into a an old speaker cone scavenged from who knows what 4 years ago, find a way to run it through a spring, then collect the sound on the other side with 2 contact mics.
TLDR
- Attach bolt to middle of speaker cone using hot glue
- Attach this bolt to spring(s)
- Attach 2 contact mics to a metal plate which is mounted to the other side of the spring
- Find a way to stretch the whole thing out
Materials
- Speaker cone (I used ~4″ – bigger the better)
- Amplifier for speaker (
- I used a Estardyn TPA3110 XH-A232 30W+30W 2.0 Channel Digital Stereo Audio Power Amplifier Board DC 8-26V 3A) from Aliexpress (~$1.50)
- Bar clamp with long jaws (Harbor Freight)
- At least 1 contact mic (You can get hella piezo discs for cheap)
- At least 1 large reverb spring
- An assortment of smaller springs (harbor freight)
- Assorted bolts, etc.
- (optional) Contact mic pre-amp
- Makes the output sound MUCH better
- Soldering tools, pliers, etc.
If I were better at documenting, there would be in-progress photos, but alas.
Steps
Mount Spring To Speaker
Find a way to attach the spring(s) to the bolt on the speaker cone. L brackets that I had lying around worked well for me. You’ll see that I also added 4 smaller springs as support – I was afraid the main spring tension would end up ripping out the middle of the speaker cone, these help make sure it isn’t pulled on to hard. I have no idea if this is necessary or not but it looks kinda cool?
Mount Speaker to Clamp
I just super glued an L bracket to the back and tied a loop of string around it. Seem to work fine for now?
Prepare Contact Mics
Strip your audio cable and solder to your contact mic(s). I used an aux cord for stereo. See my contact mic guide here for more info on this step.
Prepare Contact Mic Plate
Find something metal that you can super glue 1 or 2 piezo elements to, and also has holes for mounting the spring and clamp 2. I used a random plate with holes in it that I had, but get creative.
To prevent dampening on the contact mic side, use springs on the back side of the mounting plate to attach to the other side of the clamp. You can see my setup below. The extra plate is there because I had fabricated it for an abandoned project and it already had a bunch of springs on it.
Setup the Amplifier
Solder an audio input cable to your amplifier and solder the output wires on, which will be connected to your speaker. Connect the output wires to the speaker. Connect power to the amplifier (I made a janky 9V battery clip to barrel converter).
(Optional) Contact Mic Pre Amp
For a fuller sound spectrum, plug your contact mic output into a pre-amp first. Note that this has to be a contact mic specific pre-amp.
I also added 3D printed stands for stability.
DONE.