Magnetophone

Posted on December 20, 2013 by aaronsherwood

The Magnetophone is a sound sculpture with 14 guitar strings and 14 homemade electromagnets. Continuously generative, electromagnetic fields make the strings vibrate. Pictures available on the project’s main page.

Constructed out of aluminum and acrylic, the Magnetophone measures 3ft tall.

Circuitry

The circuitry sits atop the Magnetophone, with an Arduino Mega lowered down on a platform slightly below.

The Arduino sends out square waves to LM386 based amplifiers that power the electromagnets at the resonant frequencies of each of the strings. Its possible to sound overtones of the strings if upper partials of the harmonic series for an individual string are sent.

The circuit boards were acid etched, then treated with tinnit to keep them from oxidizing, thus the silver finish underneath. Each board has either 3 or 4 amplifier circuits, depending on which side of the Magnetophone it is being used for.

Electromagnets

I made the electromagnets out of sewing machine bobbins wrapped with 32 gauge enamel covered magnet wire.

The electromagnets needed to have 8 ohms resistance to work properly with the amplifier circuits. After a lot of testing I found that 348 turns on the bobbin with the wire was the proper number. To help with the wrapping I used an Arduino, a photocell, and a drill. I put a strip of white tape on the chuck of the drill and every time it passed the photocell the level of light changed on the photocell and the Arduino counted for me. A light comes on when the right amount of turns is reached (thanks to Eric Rosenthal for the idea). Here is a sample video aiming for 10 turns:

When electricity passes through the coil a magnetic field is generated. Since I’m sending a square wave to the coil, the magnetic field is oscillating on and off at the frequency of the wave. I put a bolt through the hole of the bobbin, which becomes magnetized and vibrates with the magnetic field. The magnetic field from the bolt pulls and releases the string making it vibrate, which makes sound. On the back of the bolt I put a small rare earth magnet. One earth magnet strengthened the magnetic field nicely, anymore actually weakened it. Instead of sending a frequency to the coil, an input coil (50 ohms resistance) can be substituted. However, I found that the string vibrates more when it’s resonant frequency is sent rather than having an input coil.

To attach the coils I designed a complex insert and locking system, that would allow me to move the coils closer or further away from the strings:

But I needed to be able to move the coils side to side as well, and found that I couldn’t do it with this system. I ended up going a much simpler route, holding the coils down in place with one strip of material above them.

Here’s a test video vibrating a string:

Instrument Design

Acoustically, the strings vibrate the bridge, which vibrates the front plate, which pushes air molecules inside the resonance chamber back to bounce off the back wall. Plywood sheets are more resonant than 1/4″ acrylic, but the wood looked a little too much like a grandfather clock to me. Plus, I wanted it to look less like an instrument.

The strings spiral up around the sides of the piece. Different gauges of guitar string were used within each side to achieve variety on each side. They are tuned to an Ab major scale, but this was fairly arbitrary, the potentials for tuning being quite wide. The tone holes are also spaced so that no tone hole is facing another, my theory being that the air molecules should bounce back and forth against the sides inside the chamber.

Arduino

The Arduino is making some decisions about what to play, and will continually keep generating new music. It switches between two modes, sometimes choosing random strings to play, sometimes generating a pattern or sequence, then looping that melody for a bit.

Using the tone library (not the built in one), the Arduino Mega can play up to six tones at one time (it has six timers). In order to reuse the timers (not a standard function), shifting them to other pins for different strings, I had to modulo the tone pin count for the amount of timers I wanted to use. For example, if I wanted to use 4 of the Mega’s timers i would do this in the tone.cpp file:

_tone_pin_count=(_tone_pin_count+1)%4;

Since I was using a Mega 2560 I also had to change everywhere in the .cpp file that said:

#if defined(__AVR_ATmega1280__)

#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)

Schematics

Here is a schematic for one circuit, and an image of the three circuit board:

Thanks

Thanks to Scott Garner for aiding me in my times of need, and to the Basic Analog Circuits class at ITP for etching a ton of PCB boards for me.

Special thanks to Danny Rozin, Eric Rosenthal, and Marina Zurkow for guidance, support, ideas, and bobbins.

Interview – Pauline Oliveros

Posted on December 5, 2013 by aaronsherwood

Pauline Oliveros did me a great honor in taking time to answer a few of my questions:

1) How do you define music?

What ever is sounding depending on how I am listening.

Noise?

What I don’t want to listen to.

Is there a difference?

The difference is in how I am listening.

2) When you’re organizing sound (composing) in your current practice, are you thinking about any of these: melodies, harmonies, rhythms, sounds, frequency relationships, form, improvisation? What kind of framework do you use for composing?

I don’t like the idea of “framework”. Too limited.

How has this changed over the years?

From just listening to what I wanted to hear and notating it to conceptualizing instructions for how to make the sounds I want to hear.

3) When you improvise by yourself how are you listening to yourself?

My ears are receiving the sounds that I make and sending the signals to my brain where I listen – interpret, decide.

How are you responding?

My body is responding as it listen.

How about when improvising with others?

No difference.

Do you consider yourself having a “style” of improvisation?

It is what it is when it is.

4) How has your practice of listening informed your understanding of the mind/body structure?

The body is faster than the mind.

How does it play into your day to day experiences?

Depends on how I am listening.

5) If the world we could see was audible what would it sound like?

How would I know?

6) Can you give me two listening exercises and two compositional exercises to do that might help me explore making my visible world audible?

Look until you sound.
Don’t look until you sound.
Compose the rhythm of your looking.
Compose the textures of what you see.

7) Where do you think the forefront of music is currently, in terms of music being created in ways that haven’t happened before?

Large group composition on the internet.

What are areas to explore that haven’t been?

I don’t know yet.

Audio-tactile synesthesia

Posted on December 5, 2013 by aaronsherwood

In another project, I’ve been building electro-magnets that make guitar strings vibrate at their resonant frequencies.

I can tune the frequency of the magnetic field to vibrate the string at it’s fundamental frequency as well as it’s upper partials (the frequencies in the string’s resonant harmonic series). This means I can change the pitch of the string between the different overtones of that particular string. Not only do I hear the pitches, but often times I’m holding the electro-magnet and I’m feeling it vibrate at that same frequency, its pretty fun.

On days when I’ve been working with the piece a lot (handling the electro-magnet, feeling its vibration, and hearing the overtones), later on, wherever I go in the City I’m feeling the rumblings and vibrations of the City, and hearing an overtone series wherever my ear can pick it out. Its pretty incredible actually.

In the course of researching ‘what the world I see would sound like if it were audible,’ the idea of synesthesia is certainly a logical choice for exploration, but I’ve avoided it for some reason. With these electro-magnetic strings, did I induce a type of synesthesia in myself? Did I somehow end up in the topic of synesthesia anyways?

Synesthesia literally means putting different sensations together. Often times we think of it as seeings sounds, but there are many different types. One such type is audio-tactile, where you feel sounds as vibrations, or vice versa. Who knows, maybe what I was experiencing was like being in the ocean all day, later on that night lying in bed you still feel the waves pushing you around, your body has a tactile memory of the ocean. But there have been studies where people have learned synesthesia. In one such study they taught a young man with aspergers to associate colors with emotions to be better adapted to social situations. As he grew older he could tell how he felt about a person based on the halo around their faces.

So maybe I did or maybe I didn’t actually induce synesthesia in myself, I don’t know. It was a cool experience none the less. What if people could feel the world in this way? A wearable device that vibrates frequencies from the surrounding environment on the wearer’s body would be pretty simple to fabricate.

Magnetophone sides

Posted on December 2, 2013 by aaronsherwood

Super-sonic listening

Posted on November 27, 2013 by aaronsherwood

One of the circuits I made in my Basic Analog Circuit class was a electret microphone amp that can have almost infinite gain. It samples itself and regulates the gain based on the input. In a quieter environment the gain can become so high that it is possible to hear things that normally the human ear cannot hear.

The ITP floor is quite noisy so nothing too out of the ordinary presents itself, though some sounds are much louder than normal:

The wooden mirror sound really interesting, though the general noise from the busy floor interferes:

I then went into the stairwell to try to find a quieter place. I had just eaten some almonds and was moving my tongue around in my mouth, and I could hear all the sounds in my mouth! Here is a recording, the mic was no where near my mouth, it sounds sort of crazy:

I then went into the back stairwell, where there are some interesting oscillations going on: