eli5,How do the Pickups in a guitar/bass work?


eli5,How do the Pickups in a guitar/bass work?

In: 18

To put it in kind of a silly way, sound is just wiggling air. Guitars make sound by wiggling the strings. (look at slow motion camera shots of guitars being played, it’s wild). Pickups detect the wiggling of the string and convert it to an electrical signal in much the same way that a microphone does — by pushing a magnet through a coil of wire which generates electricity based on the wiggling of the magnet. That signal can then be stored and converted back into wiggling air by a speaker (which the reverse of a microphone, it pushes a magnet around by feeding electricity into a coil of wire).

High school physics tells you that a magnet moving near a coil generates electricity.

Pickups are both the coil and *some* magnets, but not *the* magnets. Instead, the magnets in the pickups induce magnetism in the strings, and its these magnets which wobble over the coil and create a signal.

This is why you can’t use acoustic bronze strings on an electric guitar: they don’t react as well to magnetism.


I must confess to an ironic chuckle when I hear “experts” declaiming on the relative merits of AlNiCo 2,3 or 5, or ceramic magnets and their effect on tone, but who **never** mention the properties of the strings that actually do the work …

A basic guitar pickup is made of a row of six cylindrical magnets spaced out so they sit under the guitar strings. They are about an inch long. If you look, you can often see the six silver ends of them in a row. Sometimes they are covered.

There is a long length of thin copper wire wrapped around the magnets. I took one apart once for fun. The wire is about as thin as a hair and makes a pile about the size of a small rabbit.

Magnets are interesting things. You may have seen pictures of iron dust scattered around a magnet. The dust forms into distinct rings around the magnet that look sort of like ripples in a pond. This is a “magnetic field” that magnets are always generating. It is actually happening in all three dimensions, not just the two you see in the picture. It’s a constant bit of “power” magnets are always producing.

When you mix copper wire and magnets things get very interesting. ( [Here is a very quick video about Michael Faraday](https://www.youtube.com/watch?v=MpjoGC-Prks) if you’re interested in learning how this all got discovered.) Copper is a very friendly material where electricity is concerned. It’s like a nice, smooth highway for electrons to zip back and forth on.)

After it’s wrapped around the magnet, connecting the two ends of the copper wire completes a circuit. You can think of it like a river made into a circle. Like one of those “Lazy River” rides you can float down at the water park. The magnetic field sort of fills the river with water.

When you play a note on the guitar, the vibrating string disturbs the magnetic field. It’s like dropping a stone into the river. The ripples travel along the river path and around the circuit.

When you plug the guitar into an amplifier, you are lengthening the circuit. Making the river longer. There are two copper wires inside the guitar cable. One is taking the river away from the pickup, the other is bringing it back. (It’s hard to tell from looking at the outside of it, but the guitar plug is designed to connect to the two ends of the copper wire at two different places.)

So the “ripples” from the note you played on the guitar are traveling down the long copper wire and the get to the amplifier. The amplifier–as the name implies–*amplifies* the sound. In our illustration, it would be like sending our “Lazy River” over a cliff. That same smooth water now packs quite a wallop when it hits the bottom. The note you played with a guitar pick is now powerful enough to move the cone of a heavy-duty speaker, creating enough air pressure to make your neighbors call the police.

Meanwhile, having discharged its energy, the water at the bottom of the waterfall now travels along the second wire back to the guitar pickup, completing our lazy river journey.

Wow, who knew my guitar was just a fancy air wiggler?

Wow, so it’s like magic that turns my wiggles into sweet tunes! Thanks for the explanation!