Sound Experimentation Field Trip!

For my science field trip, I took a visit to Cumberland, RI for an afternoon with George Dussualt of Galilee Productions. Our goal- to record the super cool sound you hear when you tie a metal object to two pieces of string, wrap the string around your fingers, and put your fingers in your ears.

The main question was: How on earth can we record that sound?

THE SET UP:

It was obvious that a microphone wouldn't work because the sound wasn't traveling through air, but through objects. First, we tried mimicing the experiment with twine, but it didn't work. So, what we wound up doing was tying two PL008 guitar strings to either side of each of the objects (a metal canister and a small symbol) and threading the ends of the guitar strings into the bridge of the guitar. We held the guitar upside down so that the strings would lay on top of the pickup- in order to record the sound, the pickup needed to grab the sound coming up the strings. We hypothesized that t
he heavier the object, the higher the pitch will be (think of a piece of floss).

What is a guitar pick up? Well, on this particular guitar it is called a Piazo Element (manufactured by fish man) is a piece of copper wrapped in shrink tubing (which is the sleeve). Copper is soddered to wire *positive and negative charge at each end** there are six sensors on top (one for each top) All of it is wrapped in a shrink tubing sleeve to keep it all together. The negative side is below zero and a positive side above

WHAT HAPPENED/HOW WE RECORDED IT:

When we hit the canister or symbol, the sound is transmitted up the string, through the bridge, into the pickup. When the vibrations from the string come into contact with the pickup, they were transformed into small voltages. These volts are then transmitted through conductive cable, amplified by an “op-amp“ (VCA- voltage controlled amplifier, like a dimmer on a lightswitch), and recorded.

We had to play around with the recording in order to hear the sounds heard when our fingers were in our ears. In order to get the sound without the impact, a digital compressor was used. Dynamic compression (invented by Bill Putnam) is a means of controlling the loudness of a sound by attenuating (quieting down) it’s transient (initial impact… this can be the strick impact).

There are four components to a sound: ASDR- Attack, Sustain, Decay (how long it takes , Release. This happens with every sound. This is referred to as an envelope.

The digital compressor sets a threshold (you can set the threshold) beyond which it will NOT allow sound to get louder. But, you can tell the compressor how fast to react. We can even completely eliminate the attack (not so much with analog) You can also set how fast it releases are allows the level to come back up.

So, what we did was we did was reduced the attack of us hitting the canister and symbol so that we could better hear what came after it (the sustain). That is how we were able to hear the sound we conducted this experiment to hear.

THE SCIENCE BEHIND HOW THE SOUND WAS RECORDED:

Voltage is very small. In order for a sound to be recorded, it has to be turned into a voltage somehow. An accelerator turns pretty much everything into a voltage, and they use it to diagnose problems in submarine engines and machinery (sense vibrations that are turned into voltages which helps diagnose problems)

A voltage can be generated by a fluctuation within a magnetic field. Usually there is a circular diaphragm made out of Mylar, usually sprayed by magnetic material (gold or aluminum) and suspended inside a magnet. The voltage is sent into a wire, into a mixing console, which the voltage.

All recordings are voltages. 

FURTHER THOUGHTS/ INQUIRY:
- Turns out the heavier object wasn't necessarily higher in pitch for that particular reason. I wonder what would have changed about the pitch of the canister if we would have placed something heavy on the inside of it.
- We caught some echo from the canister when we spoke into it, but nothing happened when we said something under the symbol. This makes sense because the canister had a resonating cavity.
- What would have happened if we would have used different guitar strings? These were steel, what if they had been a different material, or different thickness? Would it have changed the tonality of the sounds we recorded?


BELOW ARE PHOTOGRAPHS FROM THE EXPERIMENT, AND ALSO SOUND FILES YOU CAN LISTEN DO ON A MAC. THE FOURTH SOUND FILE IS A FUN MIX/SAMPLE WE MADE OUT OF SOME OF THE SOUNDS WE RECORDED.
01_record_can.m4a
File Size: 3009 kb
File Type: m4a
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02_recordsymb1.m4a
File Size: 2992 kb
File Type: m4a
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03_recordsymb.m4a
File Size: 3170 kb
File Type: m4a
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04_recordsamp.m4a
File Size: 1455 kb
File Type: m4a
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