I just wondering what is the nec scale and does it affect the tone or something?
And what what are the most common scale on the market?
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What is this thing called "Compound fretboard"
Thank you!
Shorter scales have more mids, longer have more lows and highs. Longer scales take lower tunings better, but I play my 24 3/4 down in C just fine.

Mustang is 22.5, Jaguar is 24, Les Paul is 24.75, Strat is 25.5

A compound fretboard is a different topic, that's the radius. Fretboard radius is saying lets take a 12" radius for example. That's 12" of a circle's radius, that is the curvature of the fretboard. I larger radius is a bigger circle and therefor a flatter curve.

A compound radius starts with a hard curve near the nut, and gradually flattens out as you go up the neck.
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Scale length is the length of string between the bridge and the nut. For Fenders it is usually 25.5" (with the exceptions of the Jaguar and the Mustang, which are both 24") while for Gibsons it is almost always 24.75". As a very general rule of thumb, guitars with Fender DNA (Superstrats and suchlike) will tend to have 25.5" scales, while those based more on Gibsons (PRS, Yamaha SG series...) are generally 24.75". The scale length, along with the gauge of string you use, determines the tension of the string at a given pitch, so a .010 string tuned to E will be a tad looser on a 24.75" scale than on a 25.5". Generally shorter scale lengths are associated with a tone I've seen described as "rubbery", generally being a bit warmer and a bit less defined. Probably the most important impact of scale length is that it's generally easier to get a decent sound out of low tunings and/or thinner strings on a longer scale length. Besides that it's purely a matter of preference - and not a very big deal; I was, at one point, alternating quite comfortably between 24.75" and 24". Personally I suspect that people rather overstate the influence of scale length on the feel of a guitar.

A compound fretboard is one where the radius (the curve) of the fretboard changes along its length, so it's flatter at the end to allow for string bends with lower action without the strings "fretting out" (getting muted by the frets), but still have a smaller (more curved) radius on the lower frets for what many consider to be more comfortable chording. Personally I can't imagine why you'd need to go flatter than 12", but different strokes, always, for different folks.

A very round fretboard looks like this (7.25" - far too round for many people):

Whereas a fairly flat one (I think ~14") looks like this:

On a compound fretboard, quite simply, it's more curved at one end and less so at the other. 9.5" to 14" is Fender's most common compound one, I think, while Warmoth offer 10" to 16" and Jackson do 12" to 16".

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Mustang is 22.5, Jaguar is 24, Les Paul is 24.75, Strat is 25.5

Learn something new every day - I thought this was wrong but in fact the Mustang has existed in both 24" and 22.5" versions, so there you go As far as I can tell, though, all the current models of Mustang are 24".

Along with the Les Paul, all of Gibson's solidbodies that aren't baritones or the occasional limited run are 24.75" scale. Their semihollows generally follow this pattern while the hollowbody models are mostly 25.5" (Super 400, L-5, Citation), though there are a few 24.75" ones and the Byrdland, with a 23.5" scale.

Likewise, Fender's Jazzmaster and Telecaster are 25.5", like the Strat, along with the vast majority of variations thereupon. The Starcaster and Coronado, despite being apparently more in the Gibson vein, also have 25.5" scales.

It may or may not be worth noting that in the context of some manufacturers, such as Gretsch, you may see 24.6" referred to - this is actually the same as Gibson scale length, which is referred to as 24.75" purely in the interest of using round fractions, since the USA clings to Imperial measurements which tend to work in quarters, sixteenths and thirty-seconds rather than tenths and hundredths.
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Last edited by K33nbl4d3 at Dec 26, 2015,
Personally, the 2 main impact of different scale lengths for me are string tension and fret spacing. Longer scale length means higher string tension for a given tuning and string gauge, hence why it takes lower tuning better. Longer scale length also means bigger fret spacing. Some people like longer scale lengths as it can help with playing at very high frets while some people may like the shorter scale to ease the playing of stretchy chords.