Acoustic Feedback System With Snare Drum (or Any Other Object)

In this instructable I'm going to show you how to build an acoustic feedback system. The idea is to play sounds through an object of your choice (I'm going to use a snare drum that I have laying around but you can use a paint can or some aluminum foil or a cup or any kind of resonant object that appeals to you!). We're going to use a transducer to turn that object into a speaker, sort of like I did with large sheets of glass in the artwork 'Flesh++Blood':

http://www.doublearchive.com/projects/flesh_blood....

And then....we're going to attach a contact mic to that object, and route that mic into the input of the transducer, so that the object essentially 'plays' itself.

The idea is similar in some ways to a simple circuit that was designed by David Tudor for his famous 'Rainforest' piece. You can learn more about it here:

http://www.jaimeoliver.pe/courses/ci/pdf/driscoll-rogalsky-rainforest.pdf

To build this feedback circuit you'll need:

-- a computer and a usb audio interface with audio in and audio out

--an audio amplifier like this one: https://www.parts-express.com/dayton-audio-dta-1-c...

-- a jack that matches the audio in of your usb audio interface (mine is 1/4 inch: https://www.sparkfun.com/products/11143

-- a piezo disc: https://www.sparkfun.com/products/10293

-- a transducer like this one: https://www.parts-express.com/tectonic-elements-te...

-- a soldering iron and some solder

-- wires to connect it all up

-- a resonant object or surface to transmit the sound

The first thing we have to do is assemble our contact mic, using a piezo disc, an audio jack, and some wire.

Cut some red and some black wire.

Attach the red wire to the center pin of your audio jack and the black wire to the pin on the side, as shown in the photo.

Then, solder the red wire to the red lead coming off the piezo disc and the black to the black.

Be sure to wrap your joints in electrical tape to avoid a short circuit. That's it! We have a contact mic now! You can use it to record anything you like! It picks up the sound vibrations of anything that it's attached to, but be sure to firmly affix it to whatever you want to hear, electrical or gaffer's tape works well for this.

We need to attach some speaker wire to our transducer so we can plug it into our amp. Solder works well for this.

Now we can connect our transducer to the output of our amplifier.

Make sure your contact mic and transducer are firmly attached to your object. You can use tape or glue. The important thing to remember is, the transducer transmits vibration and the contact mic picks it up, so if either of them isn't well attached, then the system will have a lot of leakage ie it won't feed back, which is what we want.

You can also get some interesting effects by manipulating the contact of your transducer on your object as I'll show in a video.

Connect your contact mic to the audio input of your audio interface. This will go into your computer, and that signal will be routed, in software, to the output of your computer. Attach the audio output of your interface to the input of the amplifier and the output of the amplifier to your transducer. So what you have is, a feedback loop, which is only partially broken by the distance that the sound travels through the object to which your transducer and contact mic are attached. Make sense?

In this image I'm using Logic Pro on a mac to illustrate, but you can use any audio software. The important thing is to bring your signal in through a record channel. You may want to compress it and turn it up. The output of that channel should go to the main outputs of your audio device. You can also try adding eq and other filters to your input channel to make the sound more interesting!

This is the basic feedback circuit in action.

To get more control, download SuperCollider from sourceforge:

https://sourceforge.net/projects/supercollider/

and this repo from github:

https://github.com/socalledsound/feedbacker-sc

It will take another instructable to explain all the ins and outs of SuperCollider, but you can run that code by selecting it and hitting command+return. First, run the synthdef code to store the instrument, and then run the routine, to turn the input and output on and off in random patterns.