Science of Sound: Guitar Pickups & Faraday's Law

How does an electric guitar or bass pickup work? Hint: it's not a microphone, but it is related. Pickups, dynamic microphones and loudspeakers all exploit Faraday's law of electromagnetic induction. This video explains how, in simple terms.
References: Science, Waves & Sound Lecture Notes, sections 7 and 11.
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[@jorgemoreno6014]

Awesome. Faraday's law is all around you and the universe.

[@th-pl3nx]

I absolutely loved this video!!!!! So interesting and soooo many guestions answered. Thanks for posting!

[@kushal_rai]

This was a very well made video. Thanks

[@sadanandakarmakar9790]

Excellent lesson

[@timhope8832]

Really interesting video - would love to see the next level of detail =)

[@LousyPainter]

Very nice. Thanks.

[@alexkneifel3191]

These are great videos. I'm an engineering physics student at the University of British Columbia, who is also very into music as you are. I just started smushing these two interests together. Right now I'm machining a guitar pedal enclosure, laser cutting stencils to paint it, then will fill it up with some fuzz variant circuit :D. I've been realizing that I think I want to pursue Music/Technology in the early part of my career. Been trying to figure out what that intersection can look like. Working at a company like Roland maybe? Im not sure, but for now I learn more by watching your videos! Thanks for creating

[@ElectronicswithProfessorFiore]

Cool! Yes, an electronic musical instrument company might be a path, and there are also a number of audio gear companies out there (audiophile or musician oriented). As for videos, you might also be interested in the four part "Science of Sound" series I posted recently.

[@alexkneifel3191]

@@ElectronicswithProfessorFiore Sweet ! I was secretly hoping you'd have some more ideas haha. Thanks so much ( also cool for me to see that you're in upstate New York because I grew up in Plattsburgh!)

[@ElectronicswithProfessorFiore]

@@alexkneifel3191 It doesn't get much more upstate than Plattsburgh, with the exception of Massena! Next stop, Canada.

[@watertech011]

I never understood how a pickup works. Thanks for your excellent explanation. Very cool information.

[@FX-ri3dn]

Thank you. This was well-explained. I was wondering whether the guitar recording environment affects the guitar's sound, and I got the answer that it doesn't. Whether you play the electric guitar in a bathroom or a studio, it sounds the same.

[@Therealnonsequitur]

In a practical sense, sure. Though, more specifically, it’s the behavior of the pickup remains consistent. Environmental factors impacting the guitar itself can impact the input it gives the pickups.

[@iloveaviation-burgerclub-a8145]

Nice humor. Great show 😂 Isn't there a 90 deg phase shift or half a Pi?

[@guitaoist]

Very cool thanks for the lesson

[@tonydigregorio3806]

there are examples of yelling into a guitar pickup and hearing your voice through the amp. these conditions usually are found in older unpotted pickups with loose coils and thin metal covers (or baseplates). the cover acts like a microphone diaphragm and vibrates which will induce a signal. not relevant to your discussion but still interesting.

[@ElectronicswithProfessorFiore]

Yes, there was a bit of a conversation on this a few months back. See the other comments on this video started by JayOneAlumni.

[@JayOneAlumni]

That’s interesting. I wonder why some pickups are so microphonic that if you did yell it picks it up? Also does this mean that the wood doesn’t effect the sound of the pick ups?

[@ElectronicswithProfessorFiore]

The choice of wood affects the resonance of the body which affects the string motion which is caught by the pickups. So it is there, the question is how much influence it has on the overall sound compared to the numerous other inputs to the system. I don't have any hard data on the microphonics issues (or even any personal observations as I'm not one to yell into pickups), but I suspect it may have something to do with how they are wound. I imagine that a loose winding might be more susceptible.

[@JayOneAlumni]

@@ElectronicswithProfessorFiore honestly thank you very much for answering that question. I greatly appreciate it all the best and love your content.

[@HexuTV]

@@ElectronicswithProfessorFiore My theory is that the pickups that are covered with a metal sheet tend to be microphonic since the vibrations from the voice will make the cover vibrate, being a thin, flat, metal sheet essentially, thus acting like a sort of microphone.

[@Gearheadworkhops]

I love videos from the law firm of Faraday, Lenz and Ohm, great job. Plucking a string generates a mechanical force. That force transfers to the nut on the neck and the bridge of the guitar body. Wood is a fibrous material that becomes an acoustic cavity spreading this tiny force around causing the coils and strings to oscillate. Any movement of a conductor, even just the width of an atom will cause a current to flow within that conductor. "Loose" or "scatter winding" the coils contribute to this phenomena and accounts for the shape of the tone as these energies collide with one another. Wax potting the coils dampens this effect.

[@RayyanKesnan]

I actually just heard someone talk about this, they confirmed it was because of loose coils.

[@good.citizen]

nat atbot GPT-3 [:|o].. thank you for sharing your video file. wouldnt an ideal pickup then have a second pickup flipped up over the usual pickup and a magical string between. or, wouldnt more a magnet string and iron core 8:07 pickup. "

[@ElectronicswithProfessorFiore]

You could have a pickup above the strings but it rather gets in the way of your pick.

[@user-dd6fm2tf2v]

1:11 "stay"

[@darkmaster450]

Interesting. So that's what happens

[@JOOODYJOOODY]

OOOOPS...GOOD GUITAR PICKUPS ARE INDEED MICROPHONIC THOUGH NOT EFFICIENTLY.... EVEN TO VOICE BUT TAP ON ANY PICKUP WITH YOUR FINGER .. CASE CLOSED.. FIRST STAGE TUBE IN AMP ALSO MICROPHONIC

[@ElectronicswithProfessorFiore]

As I stated in response to a comment below, yes, it's possible that pickups can be microphonic. That doesn't mean they have to be, or more importantly, whether or not that's good. Of course, with instruments we sometimes do weird things, but in a high fidelity playback system, microphonics are something to be avoided.

[@valueofnothing2487]

You seem unprepared and constantly interrupt yourself. Picking up things and dropping them off screen is a little off putting. You seem surprised by your own conclusions. Also, you drew a bar magnet on it's side and a string above it, but of course that is not how pickups work. Bar magnets in humbuckers and p90's magnify steel poles or a given polarity which magnify the string. Vintage single coils have the string run across the top end of magnetic pole. Your discussion of the horseshoe magnet made no sense. I think you were trying to explain a the magnetic string induces a stronger voltage in a multiple coils of wire as it moves. But you just stated this simply anyway, which is all that was needed. Also, I am uncertain if your overall explanation is precise. The magnets in guitar pickups magnetizes the string. That is the important point. When the now magnetic string vibrates, it induces an electric charge in the coil of wire below it. It is this that is fed into the amp. I would not say that the string 'changes the shape' of the magnetic field. Although technically correct, it is of secondary importance.

[@ElectronicswithProfessorFiore]

I am sure that my "discussion of the horseshoe magnet made no sense" to you for the simple reason that I never discussed horseshoe magnets in this video. The closest I came to that was showing a conductor moving through an air gap as part of explaining Faraday's Law. Not the same thing. Also, the words "magnify" and "magnetize" have completely different meanings. I would expect anyone in high school or above to not confuse the two. Further, there is a difference between an electric charge and an electric current. Although related, they are not the same thing, as you seem to be treating them. I will say this much in your defense: if you had a magnetized string, its movement could induce a current in the associated coil, but then why not just sell magnetized strings? After all, Faraday's Law just says that there needs to be relative motion between the conductor and the field.

[@valueofnothing2487]

@@ElectronicswithProfessorFiore Yes I made some typos. I don't see how that's relevant. The horseshoe magnet stuff is irrelevant and badly explained. You should try to convey the key concept of what you're trying to explain with as less jargon as possible, and in the simplest way as possible. As to why they don't magnetize strings, I think it is because strings will lose their magnetism after some period of time. I don't think you could make a string under tension out of magnetic material - It would simply break or shatter. But your question does point out an interesting fact which is we don't really need the guitar string, all we need are magnets. And in fact there's a guy who sells a magnetic pick for $50 and it makes guitar-like sounds without the strings moving.

[@ElectronicswithProfessorFiore]

@@valueofnothing2487 If you do it once, it might be a typo. If you do it repeatedly, it probably indicates a deeper misunderstanding. For example, referring to an electric current as an electric charge is like confusing length or distance with speed. These are technical terms with specific meanings. It's not a horseshoe magnet. Stop calling it that. Further, that section is very much important in order to explain how Faraday's Law works, and how it applies to pickups. The bit about "magnetic strings" was rhetorical. Of course they don't make magnetic strings, and for good reason. But speaking of "magnetizing strings", take a string off of one of your guitars and see if it attracts something iron-based, like a paper clip. Then report back here.

[@valueofnothing2487]

@@ElectronicswithProfessorFiore So you were just being rhetorical? And I wasn't supposed to take you seriously? Ok. I think your video is misleading and needlessly confusing - for all the reasons I have given above. Lastly, I think you're criticizing my criticism of your use of the horseshoe magnet to explain Faraday's law. My point is that you did not explain Faraday's law with this, nor should you, nor should you even use a horseshoe magnet. The point is to explain that the magnetized string induces "a current" in the wire. There's no real need to talk about "Faraday's law" or "lines of force" or horseshoe magnets. And in particular I think you showed your hand going in between the north and the South Pole "cutting the lines of force". All I ask is why? It seems needlessly confusing.

[@ElectronicswithProfessorFiore]

​@@valueofnothing2487 Think what you will. I have no argument with whether or not you like my mannerisms, or my methodology, or even the clothes I wear. If everyone wanted the same thing, there would never be a need for more than one book or one video on any given topic. My goal in these comments is simple, and that's to prevent self-proclaimed "expert KZbin commentators" from confusing the people who come here with an interest in learning how these sorts of things actually work. Does that sound harsh? Well, the fact that you believe that it's "needless" to discuss Faraday's Law in conjunction with an explanation involving inducing a current into a coil of wire speaks volumes. It's a prime example of the Dunning-Kruger Effect in action. What's next? Would you like me to explain DC circuit analysis without using Ohm's Law? (Just to be clear, that was a rhetorical question.)

[@kokeskokeskokes]

Good day professor. Here is a diagram which is drawn with magnetic field oriented correctly for comparisson. It will also explain why. Enjoy. /watch?v=SfkX-fgmIbc

[@ElectronicswithProfessorFiore]

? We are saying the same thing. I am simply drawing something that is easy to see and which explains how Faraday's law applies here. I am not attempting to draw a cutaway of a guitar. The key takeaway is that the vibrating string distorts the magnetic field, and the resulting fluctuation in the magnetic field induces a current in the associated coil of wire (which is then fed to the amplifier, creating the input voltage which is amplified out to the loudspeaker). Sorry for any confusion.