How does an electric guitar pickup work?

Here’s the exact scenario that leads to posts like these:

  1. I become fascinated with something. In this case, I find my old guitar added with hearing someone play electric and remembering how much I love a specific guitar.
  2. I decide that I should probably get myself an electric guitar so serve this new need of mine. No delusions of grandeur or thinking that I’m going to be the next Malmsteen. I just feel like jamming.
  3. I realize that I have no money and/or have more important pending expenses in the pipeline.
  4. The obsession continues to grow while the funding does not, to the point where I start Googling “DIY Electric Guitar” and watch a billion videos and read every article.
  5. I make an electric guitar, completely or in part, and learn something valuable in the process.
  6. Afraid that my understanding of the subject will diminish, I document my findings in a forum where others might benefit from it as well.

Right, now that we’ve gotten that out of the way, just how does an electric guitar pickup work? Matter of fact, how does an electric guitar work. Let’s look at some fundamentals of sound first:

All sound, whether audible or not, exist in waves of compression and decompression of the medium in which they travel. In air, the sounds we hear are caused by something which is harder than air moving through it, and as Newton’s first law of physics states: For every action there is an equal and opposite reaction, thus the air surrounding the moving object is moved as well. Seeing as air is compressible, the air immediately surrounding the moving object is accelerated and collides with more surrounding air in the direction that it was forced, thus compressing that pocket of air. As this happens, the previously compressed air at the origin of the movement starts to decompress, thus pushing the compression outwards. Though different rates of decay exist depending on the medium that the sound wave is travelling in, this compression wave travels some distance, acting not only in the direction of the original movement, but outwards at all angles as well. Repeat this process several times per second, and the waves travelling through the air will eventually create an audible frequency as they collide with our ear drums in the same frequency as the origin. If the origin moves towards us, the frequency is compressed and the sound is noticeably higher. If the origin moves away, the frequency is expanded and the sound is noticeably lower.

By connecting such a surface to an electromagnet and rapidly varying the electricity passed to it, we can use electricity to create sound. This is the basis on which speakers operate. Higher voltage creates more powerful movements which compresses the air much denser and leads to louder audio, which higher variation frequencies causes the surface to vibrate faster and create higher tones. The opposite is also possible, which is monitoring the poles of the electromagnet for output rather than providing input. Any sound waves colliding with the hard surface connected to it will cause it to vibrate, thus creating small electronic signals as the magnet moves through the coil which can be used to create a digital version of the audio it picked up. This is the basis on which microphones operate.

Guitars make use of strings of a set open length of different thicknesses and tightness vibrate at very specific and constant freqencies. By changing the length of these strings, we can alter these frequencies to our requirements in order to produce sound in a specific key, thus creating music. In acoustic guitars, the vibration of these strings are amplified with the use of the guitar body, which resonates with the vibrations, thus moving more air than just the strings on their own and amplifying the sound it produces accordingly. Slight compressibility of the wood also allows for a much warmer and bassy tone than just the strings on their own could ever produce.

While some acoustic guitars can make use of microphones as pickups to replicate the sound they produce to be stored or digitally amplified, electronic guitars make hardly any sound at all if unplugged, meaning that microphones would be useless seeing as a microphone sensitive enough to capture the little sound that it does produce would also pick up everything else going on around it. So how does an electric guitar pickup work then?!

Imagine you have a microphone for each string, sitting next to each other in a row, but instead of being attached to a cone which physically moves a magnet, you keep the magnet stationary and move a piece of metal in front of it. The result is tiny voltage variations in the coils due to the disturbance in the magnetic field from the vibrating strings above it. An amplifier picks up these vibrations and does what it does best: AMPLIFIES THEM! Since this signal is already in electronic form, it can now be altered my means of FX pedals to create effects like delays, distortion and reverb, all by changing the waveform of the incoming signal from the guitar before sending it to the amplifier.

Now the next logical question would be: What does the inside of a coil look like? The answer: Pretty straight forward. The insides of your average 6-string single pickup is nothing more than a single row of 6x 20mm x 5mm metal rods supported at the top and bottom by a plastic (or if custom, wooden) faceplate/brace and surrounded by around 7,000 windings of 42-43 gauge epoxy-coated copper magnet wire, which is soldered onto some beefier eyelets connected to some fatter wires to be used for the internal wiring of the guitar. These copper coils are then either encased in a hard casing, or simply wrapped with some tape to protect them. The coils are mounted in such a way that their height can be adjusted, thus moving them closer or further away from the actual strings to ensure that they perform as required.

With the above being said, you can see why electric guitars can for instance not work with nylon strings, as these will not have any effect on the magnetic field being monitored via the pickups and as such not lead to any sound being produced.

If you would like to take a stab at producing your own pickups, Youtube has multiple videos covering the process step-by-step. THIS is a good example of a decent diy pickup.

Happy building!

~M