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Hi guys and gals. I think this subject was touched on recently, but I can't seem to find it anywhere, so I apologize if I am bringing up a subject that has been recently addressed.

I was recently asked "what impact does different scale lengths have on a guitar?"

So my actual question is this: On an L-00 size (for example), what differences would one expect to see in tone and playability (especially tone) between a 24.75 and a 24.9 scale length? Same exact guitar, different scale lengths.

This brought to my mind the issues of tone and playability. Regarding playability, it seems to me that there would be a little less tension on the strings, allowing for a little softer touch when fretting. As far as tone, I'm not sure.

I would love to hear your thoughts/experiences, and why.

Thanks!

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Brad Tucker

Brad,
I'm glad you posed the question, because I have often wondered about this, too. I think that a longer string will have to be brought up to greater tension to sound the same open note as a shorter string. That might or might not equate to more more energy driving the top. On the other hand, longer scale lengths increase the spacing of fret intervals, which can really affect playing comfort. Then again, a longer string is easier to bend than a shorter string of the same wire gauge. Frankly, it's a heck of a mystery to me, and I have a hunch that the most common scale lengths are based as much on overall visual proportion and tradition as anything else. I hope someone can explain this to both of us.

Patrick

Well, after finally getting some time to do a little 'net cruising, this is what I came up with.

Shorter scale lengths appear to lend some "woodiness" and warmth to the overall tone, and enhances the trebles. Of course, it also makes for a "looser" feeling guitar.

Longer lengths tend to give more power and volume, and an increase in clarity and distinction of the bass registers. And, of course, a tighter feel to the guitar.

Of course, this also plays into the whole guitar built as a system...ie shorter scale lengths could be built with lighter bracing, etc...

This is based on the premise of 2 identical guitars, other than scale length.

Anybody dare to elaborate on the why's? Or are there as many answers as builders? This subject appears to be pretty deep.....or I'm just shallow....

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Brad Tucker

It's easy to test the effect of a fairly large change in the scale length for yourself: just capo the thing up one fret and tune it down to standard pitch. This is more than an inch of change, of course; larger than you're asking about, so the effect will be clearer.

All else equal, the longer scale should:
1) have more energy at a given amplitude,
2) have a more 'true' overtone series
3) be less prone to 'bend'.

This is all simple physics, although I have to admit it took me a long time and a lot of work to get to where I uderstood it reasonably well. Sometimes I wish I'd paid more attention in math classes....

Anyway, the energy in a vibrating string is proportional to the tension and the square of the amplitude. The tension change for a given string diameter and pitch goes as the square of the length change, iirc: doubling the length with the same pitch would require four times the tension. Going from 24.75" to 24.9" increases the tension by (are you ready?) a little more than 1%. Not a huge change. Going from 24.5" to 25.4" increases the tension by about 7.5% to maintain the same pitch.

The 'ideal' strings you read about in physics books don't have any stiffness: all of the force that's trying to straighten the string out once it's been displaced comes from the tension. A string like that would have a perfectly harmonic overtone series (if it was on a perfectly rigid guitar). The stiffness of real strings shifts the overtones upward in pitch, with the higher ones being shifted more. The amount of the shift is determined by the ratio between the tension and the stiffness, and since the stiffness stays the same the ratio changes as the string gets tighter. Longer strings have proportionally less stiffness, and a better overtone series.

When you press the string down to the fret, or push it aside, the tension increases. It turns out that the amount of the increase depends mostly on the string material and diameter, much less on the length (for 'small' displacements), and not at all on the tension (unless the string is ready to break!). Pushing a given string aside in a certain place by 1/2" might raise the tension by 1#, and that would be the same whether the initial tension was 5# or 10#. That one pound of tension change is a lot greater in proportion on the string that has 5# of tension, so it changes the pitch more, and the string 'bends' easier. That's also why it's harder to get the intonation right for the shorter string.

There's a quantity called the 'impedance' of the string, which is proportional to the square root of (tension times mass). In one sense it's a measure of how hard the string can push on the bridge. A longer, tighter string has a higher impedance, so it pushes harder on the bridge. That _usually_ means that it will transfer it's energy into the guitar top a bit faster. There's a frequency dependant term in the math, so it's not a simple calculation, though.

You had to ask...

Scale lengths will effect string dynamics to be sure, but to a great degree that can be compensated for in string selection so that different scale lengths will sound the same if all other aspects are consistent. Scale length to me has more to do with the comfort of the fretting hand than with tone production.

You can take this to extremes (Bass Vs. mandolin), but if you are splitting hairs on tone differences between scales closer than 1" apart you are indeed splitting hairs. 1" scale difference is night and day when it comes to fretting feel.

Or maybe my ear is just too crude to tell the difference.

Greg N

Thanks, Alan. Great information to have (even though my head hurts now!). I was hoping that you would post your thoughts/experiences with this. So basically, a small change in length probably is not that significant?

I am definitely going to try the capo test on my 000 size which has a 25.34 scale length. I know it seems to have a lot of bass for a guitar of it's size, and it will be interesting to hear the difference.

If asked about the difference between a 24.9 and 24.75, would you say that there is not a significance in difference in tone, and a slightly looser feeling guitar?

I guess I could tell the difference pretty closely by capoing the 000 regarding tone on a 25.34 vs 24.75. Possibly it would lie somewhere about halfway between the standard tuning with no capo and standard tuning with capo at fret 1. Just thinking out loud...

Greg, I hear what you are saying, and had considered the differences if a mandolin were tuned to guitar pitch. Admittedly extreme examples I admit, and it does give me the general idea of what is going on. The mando strings would be very very loose for sure! I was just curious as to what significance smaller differences in length made on a guitar, if any. I was kind of thinking what you are saying...minimal tone changes with difference in feel. I was asked the question by a client, and was not sure about the answer, but I told him that at the least I know that playability changes, and wasn't sure how tone would be effected.

Patrick got me to thinking too, as far as the change in the downforce on the saddle, and its effect on driving the top. I know there are a couple of schools of thought out there regarding this; ie less down pressure allows the top to vibrate more freely versus more down pressure allowing for a better coupling (for lack of a better word) between the bridge/saddle and top (personally I think there is a middle ground here).

I really appreciate hearing from you guys....Thank you

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Brad Tucker

When I get asked that, my best analogy is that the difference in tone between a 25.4 and 24.9 is similar to the difference between mediums and lights on the same guitar.

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http://www.chassonguitars.com

Kent makes a good point. Changing string gauges isn't exactly the same as changing scale length, in terms of the effect on tone or feel, but you can take a 24.75" guitar and a 25.4" guitar and string them up with nearly identical tensions by the choices of gauges you put on. You could even make the 24.75" guitar have higher tensions. So, scale length and string choices are two parts of the same equation. And then there's how stiffly the guitar is braced in relation to the amount of tension a given set of strings puts on it, which is another part of the same equation as far as the tone is concerned.

I would have to differ on the point about scale lengths having a big effect on comfort of the fretting hand. I think this is a subjective thing, and, to some players it may make a big difference, but it doesn't to me. I have a baby Martin travel guitar with a very short scale, and another guitar I play a lot with a 25.6" scale, and I hardly notice the different spacing of the frets. After a few seconds of playing, my hand has adjusted, and it's just another guitar. It's different, yes, but it's not an issue or an impediment in any way. Even with a fairly large difference in scale lengths, the actual difference in the spacing of the frets within a hand's span on the neck is pretty small.

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

I dont think you will notice much of a difference between 24.75 and 24.9 - thats only .150 - it would be similar IMO to taking a 24.9 and tuning slightly flat - does the tone change all that much ???

To Todd's comment on widely varying scales - going shorther than std is likely easier than say going from std to baritone - the stretches are now very noticable. Most who try a bari get used to it, and most end up playing different pieces on them, but at first its a bit daunting to some.

One of my good friends, independant jazz artist Sean Meredith Jones has played a number of my guitars, and being a Pat Methany nut was very keen to get his hands on a baritone - when he first started playing around with one the first thing I notice him struggling with was some of the stretches in his chord voicings - not that he didnt find his way around in short order, but its certainly a change in mindset.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

All excellent points. I really appreciate the information!

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Brad Tucker

Brad T wrote:
"Patrick got me to thinking too, as far as the change in the downforce on the saddle, and its effect on driving the top. I know there are a couple of schools of thought out there regarding this; ie less down pressure allows the top to vibrate more freely versus more down pressure allowing for a better coupling (for lack of a better word) between the bridge/saddle and top (personally I think there is a middle ground here)."

I'm not at all sure that break angle by itself effects acoustic tone. Certainly it changes the way an undersaddle pickup will sound, but that's another matter. So long as the string remains in good contact with the saddle the full transverse force of the strings should be there to move the top. You only need about 10-15 degrees of break angle to maintain contact; more than that shouldn't make any difference.

There are two ways to alter the break angle on a steel string guitar; raise or lower rhe saddle height, or ramp the string slots. I can't detect any difference in tone when the slots are ramped, but that could just be my lousy hearing. OTOH, poeple do tend to hear what they think they will hear, and if you believe that ramping the slots will change the sound, maybe it does for you.

Raising or lowering the saddle does change the sound, and this can be measured. The string changes tension twice for every cycle of vibration, and that twice-per-cycle tug on the bridge top does produce some sound. Raising the string height off the top by putting in a taller saddle gives the tension change more leverage, so it produces more sound. It's not that the guitar gets a lot more powerful, but the timbre does change, and it might sound 'louder' or 'richer' to you.

I'm in the process of setting up a better place for doing sound output measurements, and maybe, at some point, I can nail this one down.

Thanks, Alan. I had noticed that some of my guitars sounded "louder" to my ear with a taller saddle. Of course, I have too many variables in building to quantify that, and it could have been some coincidence. I have noticed a change, although very little, during the set up process, as I initially run my saddles high, then work them down to proper action. But, one can really hammer down on a guitar with an extremely high saddle initially, creating the illusion of loudness when in fact it's just more aggressive playing, which is where I see an illusion of higher saddles=louder guitars potentially forming. But then again, as you point out, maybe it's not an illusion at all, but a change in something that may be construed as loudness.

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Brad Tucker

And I thought long division was hard!

For sure, Tony. I was talking about the differences between standard guitars, ranging from 24.75" (or even all the way down to 23", in the case of my little Martin) up to 25.7". When you get into baritones, basses, etc, the stretches involved for the left hand start to be something to contend with.

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

I've found this to be very interesting and informative, so I'll thank Brad again for starting the thread, and my thanks also go out to everyone who responded. Best regards to all.
Patrick