1

What would be the issue/effect of having the bridge too far away from the nut on a large fretboard with standard fret sizes? For example, a 24 fret board with 25.5 inch scale fret spacings, but a bridge 28 inches away?

  • See this calculator – david strachan Mar 18 '15 at 9:56
  • Is this just a theoretical question? As a guitar neck is not adjustable in length or size of frets, thus fixing the bridge in only one optimum position. – Tim Mar 18 '15 at 11:06
  • @Tim What about guitars with adjustable bridges as with a fixed tailpiece. – Rockin Cowboy Mar 18 '15 at 13:09
  • @RockinCowboy - Why would anyone want to put a bridge in anywhere except the right position? No guitar is going to play in tune like that. – Tim Mar 18 '15 at 16:28
  • @topomorto - changing a neck for one of a different scale is, I imagine, quite rare. A similar neck from the same model would make sense, but otherwise major surgery probably wouldn't warrant such a swap. – Tim Mar 18 '15 at 16:30
4

All the notes would play flat (lower in pitch). The 12th fret (for example) should normally be halfway along the string, so that it sounds an octave higher than the open string. If the bridge saddle is further from the 12th fret than the nut is, the 12th fret would play a pitch lower than the octave above the open string.

  • Thanks. I suppose the saddle screws are for fine intonation adjustment. Well, that sucks! I really want a huge neck but can't get the bridge close enough. – Luke Faez Mar 18 '15 at 9:38
  • @LukeFaez Get a cheap second-hand guitar and do some woodworking. or stick a guitar neck on an old bass... or any old plank of wood... – topo Reinstate Monica Mar 18 '15 at 12:56
6

Not only would your fretted notes play flat, but as you go further up the fretboard, the flatter your notes will get!

3

The fret spacing (distance of each fret from the saddle) is very precise for any given scale length. Many guitar manufacturers stick with common scale lengths so they don't have to constantly re-calculate the fret spacing. But the scale length varies between guitar builders and some even offer options for different scale lengths.

Moving the bridge even a tiny bit will totally change the intonation and result in a new tuning that will not sound correct with any other instrument. You will be able to get one fret to play in tune, but all the other frets will be out of tune.

Even guitars such as an arch top that have a movable bridge must have the bridge located in precisely the correct location. If a movable bridge gets knocked out of position, and there are no markers on the top to aid in placing it back in the exact place where it is supposed to be, then you can find the correct place by playing a harmonic at the 12th fret and comparing the sound with a fretted note at the 12th fret. Keep moving the bridge until both notes are the same.

The only way to get the guitar to play in tune if you move the bridge is to move each fret to the precise location it will need to be in for whatever new scale you create.

You could use a neck for a baritone guitar which is set up for a longer scale and place the bridge in the exact spot for proper intonation, checking with the 12 fret harmonic method mentioned above.

An experienced luthier will know the mathematical formula to calculate the exact fret locations for any given size scale. But in order to make that work with standard measuring devices, there are probably numbers that work better than others for scale length measurements.

  • The formula for frequency (in equal tempered intonation) is simply that a semitone is a frequency ratio of the twelfth root of 2. Thus both the scale length and the fret spacing diminish by this amount for each successive fret. This doesn't take into account the effect of string stretching as it is bent to fret the note, but using the theoretical ratio and posiitioning the bridge to compensate would probably be good enough. Apparently the luthiers of the renaissance used 18/17 as a ratio, although this is a whole cent too narrow. – Level River St Mar 18 '15 at 15:20
1

As already said, this will completely change the tuning on all frets. So, the only way this could be usable is if you want to play in a tuning other than the western standard 12-edo. If you move the bridge only slightly, the lower frets will still make up an approximately equal-tempered tuning, just with another step size. Making the scale a bit shorter could thus give you an 11-edo tuning – 10-edo would already be problematic because the higher frets stop giving the same frequency ratios. Increasing the scale could give you 13-edo and 14-edo.

All those tunings are pretty exotic, I don't think you'd likely have much fun with them! Though there is one tuning you can achieve this way that I find quite fascinating. It's not an edo-tuning but an edt-tuning like Bohlen-Pierce (i.e., it does not have octaves at all, only tritaves). It is the 17-edt tuning.

I actually have a guitar modified for that tuning, by inserting a secondary “bridge” over one of the pickups:

17-edt paula

An example of how this can sound:

  • Wow, this is really interesting. I'd love to know a bit more about the kinds of sounds/music you create with this instrument. Just not sure that a comments stream is the best way. Maybe another post...? – Bob Broadley Mar 18 '15 at 23:13
  • 1
    I'd love to say something more about this, but frankly I haven't finished anything else yet in 17-edt tuning. There's a lot of handwritten ideas, some sketches about how the theory would work out, but nothing really definitive. I've occasionally just tried improvising something on the guitar, but to little avail. Trouble is, you basically need to purge everything you know about western music from your mind: because the chromatic steps in 17-edt are so similar to 12-edo, you easily end up playing detuned diatonic melodies instead of scales that make harmonic sense in the odd 7 (or 11) -limit. – leftaroundabout Mar 18 '15 at 23:39
0

You could possibly get this to work by having a temporary bridge - possibly just a piece of wood with an acoustic guitar saddle strip - resting on the belly of the guitar. It would be held in place by the string tension. It would be necessary to take out the existing bridge saddles etc. The rest of the bridge would remain to anchor the strings.

It would be extremely ugly though! You would have to forget about using your tremolo, if you have one.

  • banjos have a bridge which just rests on the skin and thus is very easily moveable. One thing that is frequently overlooked when restringing a banjo is proper positioning of the bridge to achieve correct tuning on the higher frets. – Level River St Mar 18 '15 at 15:11

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