Sound to electricity and back again

Hello aspiring builders. Today we won’t discuss volts and amperes - we’ll save that for later while it all sinks in a bit. Instead, we will discuss a process that tends to confuse a lot of newcomers: how does sound get turned into an electrical signal and back to sound again?

Basically, a sound and an electrical signal are one and the same. Both can be described with an amplitude and a frequency, and can represented on a two dimensional graph. That’s it, there’s no magic (not *actual* magic, at least).

Electric guitars have pickups. We already know and love these guys. Pickups are made of small magnetic cores, wrapped with many, many turns of fine copper wiring. Guitar strings are also made of metal ( \m/ ). When we hit a string, it vibrates and its movement disturbs the cores’ natural magnetic fields, inducing electron activity in the copper wiring. This induction generates an electrical current in the wiring at the exact same frequency as the vibrating string, at an amplitude that’s proportional to the amount of wiring wound around the cores. The result: our guitar sound turns into an electrical signal. Sorcery!

Now that we’ve figured that out, what about the other way around?

Our electrical signal has quite the adventure ahead of itself. It will travel through pickups, a long cable, some pedals, an amplifier and all the way to a couple of speakers, fighting its way through stray capacitance (keyword!), output and input impedance (more keywords!), losing some of its power (keywords for everybody!) along the way. We’ll worry about these eventually. For the time being, all you need to know is that when a signal finally reaches a speaker, it goes through the exact same process of induction, except in reverse.

Speakers are built upon the same principles as our pickups, with a magnetic core and copper wiring wrapped around it. The current from our signal will induce changes in the core’s magnetic field, again at the same frequency as the signal. Changes in the magnetic field will produce physical movement in a coil attached to our speaker cone, thus making the air around it vibrate, which translates to sound in our ears.

There we have it, we plucked a string, our guitar pickups turned the motion into electricity and a speaker did the exact opposite. Amazing.

Next time, we’ll get into the dirty stuff, promise.