Would this proposed guitar modification work?

October 9, 2007 3:40 AM

Crazy idea for a modified guitar - has this been done? is it feasible?

Imagine you took a normal steel-string acoustic guitar. On the fretboard, in each of the spaces between the frets (where you sometimes get dots or other types of inlay) you inlay a thin bit of metal, parallel to the frets but flush with the surface of the fretboard, stretching the width of the fretboard. These bits of metal are actually powerful electromagnets (so they have some arrangement of coils inside). Therefore, when you press the string down (in between the 2nd and 3rd frets, for example), assuming the magnets are turned on, the string "sticks" to the fretboard (held by the magnet). So if you were to take your fretting hand away and pluck that string, it would be 3 semitones higher than the open string. To release the string, you just turn off the electromagent with a footswitch or something. It's like having a capo that you can set individually for each string. Using a guitar like this you could play stuff that wouldn't be possible on a normal guitar - for instance, you could fret a C chord (which would then stay effectively "pressed down") and then play a melody much higher up the neck while continuing to play the chord using the lower strings. I'm imagining a fingerstyle type of playing here.

Has anyone made such a guitar? Is it technically impossible?

posted by primer_dimer to grab bag (24 comments total)

"... Has anyone made such a guitar? Is it technically impossible?"
posted by primer_dimer to grab bag

I don't, personally, know of any person who has successfully created such a thing. The major problem I see, as a guitar player, is that the string deflection force necessary to play fretted notes on the average electric guitar can be several pounds of point pressure.

No magnetic field, however strong, could create the force necessary to pull down a low "E" string, of normal construction, and magnetic permeability, under normal tension, without affecting, whatever, adjacent strings.

But before the Wright Brothers flew, nobody thought wing warping was a good idea, either. Ultimately, it didn't prove to be a great way of making airplanes, but it got them off the ground, and into Army contracts.
posted by paulsc at 4:15 AM on October 9, 2007

Sounds difficult because you'd need some very powerful electromagnets to hold on tightly to a very narrow string.

You might have better luck with a couple of these.
posted by mmoncur at 4:17 AM on October 9, 2007

I think you'd have some pretty big problems with the pickups, even if you could get the strings to stick. Magnetic fields from the inlays plus magnetic fields in the pickups = no worky.
posted by onedarkride at 4:26 AM on October 9, 2007

onedarkride, he specifically mentioned a "normal steel-string acoustic", so that wouldn't be an issue (that was my first thought too but I caught myself on the re-read).

OP, that's a pretty interesting idea. I don't know enough about electromagnetism to know how well it would work. What paulsc about affecting adjacent strings makes sense, unless there exists electromagnets so specifically directional that they could be "aimed" to only influence one string.

Still, this would be an intriguing idea for a built-in capo for any fret (just make the electromagnet a bar under each fret and have all six strings depressed). Not so sure about the one-per-string idea though.
posted by sprocket87 at 5:45 AM on October 9, 2007

Intriguing idea. One thing I don't understand:

Step 1: you turn on the electromagnet with a foot pedal. Now any string that comes near the electromagnet, i.e. the fret, will stick.

Step 2: you fret a C chord. The strings all stick and you've capoed a C chord.

Step 3: you play higher on the neck. Here's what I don't understand: each time you play anything higher on the neck, as long as the electromagnet is still on, the string will stick there, and you'll keep capoing stuff higher and higher on then neck.

Step 4: when you're done playing in C you turn off the electromagnet with the foot pedal. Everything comes unstuck from the frets. This part I understand.

So if I understand your scheme, there's a problem betwen steps 2 and 3. You would need to have some system where you fret a chord and then hit the pedal, and the pedal somehow only turns on those electromagnets where the strings are touching; and then you hit the pedal again to demagnetize. Or else only lay the electromagnets along the first 3 or 4 frets so you can play simple open chords like C, D, G etc. and then play higher where there are no electromagnets. But even then, pushing down the string higher up might bring the string close enough to one of the magnets lower down that it shifts the capo up a fret or two, so to prevent this the magnets shouldn't be too strong; and yet fingering a string higher up could also dislodge the string from the magnet lower down, so they would also have to be strong enough to really hold the things down securely.
posted by creasy boy at 6:08 AM on October 9, 2007

good point, creasy boy. I'm imagining some sort of electronic component that can "tell" when the string has been pressed down and "turn off" all the electromagnets higher up the neck.

Tenstion-wise, I guess the obvious thing to calculate is the pull generated by an electromagnet of reasonable strength on a bit of metal of given surface area (the string; as mmoncur points out, this will be very small) that's in contact with it. Then ask, is that enough to hold down a guitar string (assuming a nice low action). Anyone know how to calculate the former?
posted by primer_dimer at 6:19 AM on October 9, 2007

s/Tenstion/Tension/
posted by primer_dimer at 6:19 AM on October 9, 2007

I have to admit that I'm pretty convinced that this won't work, even though it's a very cool idea. The obvious implementation is very small electromagnets vertical (i.e. perpendicular to the frets) Having 6 magnets (1 for each string) between each pair of frets is the way to do this, though really, mmoncur's solution is much more likely to work well.

One thing which might help:
There are very strong permanent magnets which are very proximity sensitive. You may have seen them somewhere: they are essentially a block of metal with a mechanical switch on the side. When you turn them on, the magnet moves closer to the casing and they stick with great force. When you turn them off, the metal moves away. Perhaps that might be a better choice than electromagnets.
posted by JMOZ at 6:39 AM on October 9, 2007

While you could never get electro magnets strong enough to work in this scheme, there is a slightly possible workable scheme that is rather similar.

Have each fret separated into 6 segments with solenoids mounted under each segment. Somehow in your playing you can cause the segments to pop up to hold a position and somehow you can make them pop down.
posted by MonkeySaltedNuts at 6:45 AM on October 9, 2007

You could circumvent that by only having the magnets on, say, the top 5 or 6 frets, which would allow you to solo to your heart's content down below.

That said, I don't see magnetism being the answer here. If you had to do it mechanically, I'd figure out some kind of system where you could quickly guide the strings into hooks or slots, then release with a foot pedal.

I think a more feasible idea would be to set up a computer between your guitar and the output speaker. Handle each pickup individually, and do a transform on the output. So, I'd hit my foot pedal and strum a C. This would tell the computer to lock in that set of notes. Then, anytime it heard me play an open note, it would transform (or substitute) the appropriate note from the C. If it heard me play a higher note than expected, it would let that channel pass through.

It'd be a little bit tricky algorithm, but probably more realistically possible than the magnetic idea.
posted by chrisamiller at 6:46 AM on October 9, 2007

For what it's worth, I've been pondering ways to make an automated guitar, and the best idea I had were some kind of hooks that could emerge from the fretboard, grab a string, and pull it back down. (using a solenoid).

Imagine an L-shaped metal bar or hook mounted in a hole at each fret of each string. Ideally they would start parallel to the string, raise a half an inch, rotate perpendicular to the string, then pull back.

I'm sure a solenoid could handle this but I haven't figured out how to add the rotating motion necessary to catch or release the string.

I'm just throwing that out there in case it's a better solution to your idea. My guess is that, despite the complexity of such a system, it's more likely to work than pure electromagnetism.

On a slightly less insane note, you could probably accomplish the same thing in software if you used one of the MIDI / virtual guitars. For example, Fender's VG Stratocaster has a rotary switch to change tunings, which works since the sounds are produced with a virtual model instead of directly by the strings.
posted by mmoncur at 6:47 AM on October 9, 2007

Note to self / other crazy tinkerers: if the hooks were instead loops, and went around each string, they could extend (hopefully to a point where they don't touch the string) and retract using a simple solenoid.

Would cause serious issues if you wanted to fret by hand, though. Hmmm.
posted by mmoncur at 6:50 AM on October 9, 2007

on further thought, my scheme (fret segments with solenoids), I don't think you could get the solenoids strong enough. However you might be able to get it to work by using pistons powered by compressed air or hydraulic fluid.
posted by MonkeySaltedNuts at 6:52 AM on October 9, 2007

In addition to the problem cited by creasy boy, another problem I imagine is this: Any magnet powerful enough to hold the string while you play it would be powerful enough to grab the string before you fretted it, so you'd wind up capoing the whole fingerboard when you activated the magnet.

Here's a high-tech alternative, which would only work with an electric. Cover the fingerboard with sensors that will register when a string has been fretted over them. Run the guitar's output through a digital-signal processing application of some sort (insert lots of handwaving here). You'll add a pedal to your setup that tells it to "capo this"; when you press the pedal, the fingerboard sensors acquire your current fretting and feed that into the DSP app, which alters the signal coming off your pickups to simulate that custom capo configuration.
posted by adamrice at 7:13 AM on October 9, 2007

Well I passed this question along to my dad, who is a guitar player as well as an electronics and mechanics guru. His reply had some interesting tidbits, mostly confirming the comments thus far:

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I agree, it would take an immensely powerful electromagnet to maintain the attraction of the string. There are a few things that make a electromagnet (hereafter referred to as emg) strong. More windings can make it strong, but increases size. Thicker wire + more current equals stronger, but again, it becomes larger, as well as more difficult to power. Six emgs would have to be able to fit side by side. More current draw equates to the dissipation of heat because of inherent losses in the emg. Sufficient current could demand a stout power supply.

I have seen security emg locks that seem incredibly strong, running on 24 volts at a surprising low 200 millamps. However, there was a larger plate surface area contact. You will break the door before you seperate the lock, but again, it is a large surface area.

Thermal changes in the neck (from the emgs) could, of course, create tuning issues.

The attractable surface area, "where the string is pressed", is so very small, it drastically increases the difficulty. Imagine how thin you can get with a light gauge high E string.

Also structural integrity of the neck due to 6 times X Frets emgs would be a whole other matter. I think the same goes for an emg bar that would capo all 6 strings at once.

If I am not mistaken, bronze is non-ferrous. The E-A-D strings of course, are often bronze wound on acoustics. I suspect this would impede the effect.

Alternating current would likely be unusable, the frequency of the AC would be translated into the string "audibly". The pickups on an electric guitar would certainly be sensitive to the AC emg field... just bring a cell phone near a pickup for a idea how sensitive they are. It is possible to filter out a specific frequency, granted, but it complicates it more.

Even with DC, the sudden energizing of a coil creates a large em field. In circuit, the resultant electrical spike has to be dampened, or it can destroy adjacent circuits. With an electric guitar, the sudden energizing and collapsing field would at the very least, create a click sound in related or nearby sound gear.

For an individual emg application, Hysterisis would come into play. The delayed release would possibly affect some things you might be playing.

Fat fretted axes like Gibsons would increase the difficulty for obvious reasons.

Would it "hold" when really wailing, or bending notes as with blues style?

But if it could be done....
Wow, you are right, it would make for some cool possibilities. Perhaps even involving something preprogrammed. I like your thought about striking a chord, it holds the chord, then your fingers are freed up to some melody/scale stuff.

Maybe part of the answer to this may lie with revamping string technology to be more compatible. Also perhaps the neck could be built from a composite or titanium (wow $$$) technology for strength. Then perhaps that could overcome the weakend neck scenario.

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posted by sprocket87 at 8:42 AM on October 9, 2007

Instead of magnets and electricity, you could build a segmented capo device, similar to the mechanical portion of an autoharp, that would attach and completely cover the first three or four frets and have a locking mechanism with a quick release.

Then, rather than fretting chords in the first position with your fingers directly on the strings, you would change chords with controls similar to those on an autoharp, locking the chord into place, and then fretting normally with your fingers on frets above the autocapo mechanism.

So basically, you would create a guitar with an autoharp interface for first position chords and a quick release mechanism.

The Autocapo could even slide up and down the neck to wherever you want it.

It would be cool. A Guitautoharp. An Autoguitar. An Autocapo.

And I call dibs on the patent and all other intellectual property rights to what I just invented.

With guitar, mechanical solutions are almost always better than electric ones.
posted by The World Famous at 10:05 AM on October 9, 2007

OK, wait, I've got another idea.

Each string has its own mechanical capo. Each capo is attached to a track running the length the neck on the back, which allows it to slide up and down the neck, and has some kind of transport that moves the capo up and down. Normally they'd be in their home position at the nut.

When you hit the "capo this" pedal, they'd slide down until they hit your fingers. A simple switch built into the leading edge of each would stop their forward travel and press them down against the strings at the current finger positions. This would be robotic and scary/cool looking, and probably sound like hell.
posted by adamrice at 10:35 AM on October 9, 2007

adamrice, that system could even by gravity-driven, rather than mechanical or electronic. The individual capos could rest above the nut and roll forward on the strings when the guitar is tilted so that the headstock is above the guitar at a given angle. They would stop wherever your fingers happened to be at the time. They could have individual locking mechanisms, actuated by pushing on top of them with the fingers. A single release mechanism could release them and they would roll back above the nut when the guitar is tilted headstock-down.
posted by The World Famous at 10:53 AM on October 9, 2007

TWF: You're right, and that would be an interesting path to follow. I'd vaguely imagined a rocker that would use the force along the direction of travel to depress the capos when they reached their stopping points; that would be possible with gravity power, but would require enough momentum that it might interfere with playing.

Still. Cool idea.
posted by adamrice at 11:23 AM on October 9, 2007

You would definitely have to learn to play with it, and operating the capos with your fretting fingers while still playing would be tricky, but probably not impossible.
posted by The World Famous at 11:29 AM on October 9, 2007

Capomatic, anyone?
posted by sprocket87 at 11:38 AM on October 9, 2007

Just do away with strings all together, and replace them with laser beams or a touchscreen fretboard. Then its simply a matter of programming in different tunings for each "string", which can be activated by a foot pedal. I think you'd have more joy designing something like this than working with magents and solenoids, although i imagine playing a stringless guitar would take some of the fun out of it.
posted by robotot at 3:07 PM on October 9, 2007

Then its simply a matter of programming in different tunings for each "string", which can be activated by a foot pedal.

Or just buy a Roland VG system and use 10-year-old technology to do exactly this while still using actual guitar strings ;-)
posted by The World Famous at 3:32 PM on October 9, 2007

Many good answers, thanks.

adamrice, that sounds good except for chords where you want some strings to stay open (i.e. the capo-lets would never hit your fingers) and barre chords (where the 1st finger would stop them all at the same fret).

The World Famous, I like the sound of the AutoHarpGuitar. Maybe the buttons could be on the back of the neck, so you could play them with your thumb.
posted by primer_dimer at 2:29 AM on October 10, 2007