SC 2017 Semilab: Electricity and Sound

by Alex Treyer

If you ever stood next to a big subwoofer while it was playing a tune, you may have realized that sound is some sort of a mechanical wave that passes through the air, pushing it around and making it vibrate. You would feel these vibrations with your ears, or chest, depending on how loud you like your music. Most musical instruments are built in a way that allows them to generate certain vibrations, as controlled by the player, and then propagate these vibrations through the surrounding air (or to an amplifier and speakers, like in the subwoofer example, which in turn does the same thing). The qualities of these sound waves are defined by the instrument’s mechanical components – the strings, the wood, the brass, the drumheads, and the list goes on.

At the beginning of the twentieth century, scientists and engineers who studied various effects of electricity discovered that electric current could be used to control vibrations of certain mechanical components of machines, and that such electro-mechanical machines were capable of producing sound in a way much like a musical instrument, by tuned changes in their electric current. Later, in the 1950s, physicists and musicians together began designing, or synthesizing, custom waves of electric current and using them as a source of sound. Their idea was that a wave of sound could be given any desired shape, provided that one could make that shape appear as an electronic signal first. To this day, their concept continues to make for a tremendous variety of sounds possible, to the great joy of electronic musicians worldwide. But what do we need to do if we want to shape electric current and transfer it into sound?

Our series of semilabs will focus on understanding and putting together the key components that make up an electronic circuit-based sound synthesizer, much like the simplest synths of the 1950s. We will go over wave generation, amplification, and filtering, and will try to visualize various waveforms we can produce. We will look at the qualities that a sound can have to the ear, and how these qualities are carried in the wave shape. We will attempt to wire up some circuits first hand, of course, or use pre-wired examples for the more complicated engineering parts. This lab will give you a basic appreciation for both the fun and the hard work of designing sound with electronic circuits.

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