String Tension and Stiffness (aka Compliance)

Craig Bumgarner

Craig Bumgarner wrote:

I can't see a connection between the finish and the neck angle. I don't think neck angle increases string tension which is a function of the string mass (gauge), length and tuning pitch.

anthon_74 wrote:

Interesting... Okay, so then I have a mystery on my hands

I have 2 guitars, one is an alta Mira M01 which is a 670mm scale, and a Gitane DG 300, which is a 680mm scale.

I have BOTH strung with Argentines the heavier gauge, yet there is a very noticeable difference in string tension between the 2 guitars, the Alta Mira having the higher tension of the two.
I assumed it was because of the neck angle, which is very pronounced on the Alta mira, so much so that the bridge is almost a 1/2 inch higher than the Gitane, but the action is basically identical.

Given these factors, why does the gitane have such a lower string tension ?

Anthony

Okay, I don't doubt your perception. "Tension" is a function of the mass of the string, the length and the pitch it is tuned to. If the tension changes, the pitch changes, so assuming identical scale and string mass, if the tension were higher on one guitar, the pitch would also be higher.

To avoid confusion about tension, many people refer to what is felt by the fingers on the string as "stiffness". Lots of things besides tension can affect stiffness, even if the tension is the same.

If the Gitane DG-300 has a longer scale, identical strings should feel stiffer because identical strings have to be brought to a higher tension to achieve the same pitch with a longer scale length. (Are you sure the DG-300 is really 680mm? I know that is what the manufacturer says, but 680mm is pretty long. You know how to measure scale length right? Distance from zero to the 12th fret x 2). But if 680mm, the 680mm guitar should feel stiffer. But it doesn't, so what else could be at play?

Just cause I build guitars doesn't make me an authority on anything, but here goes. Assuming identical strings, scale length and concert tuning, though, here are some factors I can think of that will vary the perception of string stiffness. There are probably more 8)

• Action, higher action will feel stiffer and it does not take much. A tenth or two of a mm will make a noticeable difference.
• Nut or zero fret height
• Neck relief
• Neck size
• Fret height
• Neck and body flex
• Finger placement (I'd assume though you play the same on both guitars unless neck shape differences force you to do otherwise).
• Break angle across the nut and bridge IF the strings are mobile across these points. This is much debated and even string manufacturers refer to this. You can read about the confirming side of this debate here: http://www.frudua.com/guitar_strings_tension.htm. The basis here is that a string with shallower break angles over the nut and the bridge and longer string lengths after the break will allow more movement of the string over the nut and bridge, allowing the string to yield more under finger pressure. The steeper the break angle, the shorter the string after the breaks, the stiffer the string will feel. A steeper neck angle usually results in higher break angle at the bridge. The effect of break angle on tone is another issue, discussed here from time to time and worth more, but won't go into that here.
  
  I'm prepared to wrong on this, but my personal speculation is while this might well be true in theory, it hinges on the mobility of the string over the nut and bridge. On Selmer style guitars with relatively high break angles, short lengths after the breaks and sharp edge wood bridges, I don't think there really is any, or what there is miniscule. Also, the break angles and string lengths after the breaks vary considerably from string to string in Selmer style guitars (have a look) and I don't perceive a corresponding difference in stiffness. This theory about break angles should be easy enough to measure. I note the Frudua article does not put forth any measurements to confirm their theory. Probably someone has, I have not, but this thread inspires me to do so. I'll be back later on this, who knows, maybe with a plate of crow to eat .
  
  Anyone have ideas or references on this?
  

Craig Bumgarner

Something I just thought of is the rocking of the bridge. Though the string may not move in the bridge slot, the bridge rocks some under the sting vibration when plucked. It might rock more under higher break angles because of the added leverage, which would in turn might make for a looser feel. Or maybe the higher break angle locks the bridge down tighter, reducing the rocking, imparting a tighter feel. Rocking is also a function of at least the base width, fit, contact area and top & brace support. yeah, it's complicated.

EDIT) After some consideration and reading, I don't think the bridgecan really rock sufficiently to make a noticeable difference in string feel, , at least in the case of Selmer style guitars.

SteveG

I think you might be coming to terms with what is referred to as "compliance". A quick search will yield lots of discussion and not too many firm conclusions. cheers, Steve

Craig Bumgarner

Steve,

Thanks, yes, compliance is a good word and does seem to be the more common term for what I was calling stiffness.

I like this discussion... Scroll down to where Alan Carruth and Trevor Gore post:

http://www.classicalguitardelcamp.com/v ... 11&t=76492

Also, this one by Liutaio Mottola, especially the section about "Human Perception of Tension and Compliance" where he sited Bob Benedetto's informal tests.

http://liutaiomottola.com/myth/perception.htm

anthon_74

Okay, so I have not actually measured the two guitars, but when I put them next to each other, the Gitane is noticeably longer by about 1/3 of an inch. I don't know what that is in mm. the reason I said 680 is because that's what the specs say on Michael's website concerning the Gitane dg 300 and the Alta Mira M01. now, my gitane is over 7 years old, so I'm not sure what the specs were back then,

In any case, this is definitely not an action issue, as the action on both is virtually identical. It is very pronounced that the gitane's strings are much less stiff then the alta mira's. When I bend a string, it is much easier to do on the gitane. It's so pronounced that I just ordered a set of lights to put on my Alta mira so the strings play a bit less stiffly.

In terms of the neck, they both have a U shaped neck, but the Gitane's neck is much thicker. The Alta Mira neck is almost like a hybrid between the U and the C shape, and plays like a dream.

It sounds like nobody can give a definitive answer on this...Maybe next DIJ I will bring both guitars someone can try them and see the difference.

Anthony

SteveG

Is the action really the same? Neck relief the same? Scale length not responsible for the difference in feeling? Scale length can make a big difference.

How are you measuring the "stiffness" ? If it's a difference in "feel" or "slinkiness" rather than the effort to hold the string down, it could be the frets. Polished frets feel different than worn ones. Taller frets feel different than shallower ones. And harder frets (like stainless steel or Evo) are slicker and are easier to bend notes on than nickel silver frets.

Just some thoughts. cheers, Steve

Al Watsky

Guitars are fascinating.
Head stock angle is a big factor.
Bridge break angle, major.
Scale length is primary.
The bridge movement is often dictated by the elasticity of the top.
The rocking motion starts as a momentary deflection of the whole top.
Then the wave starts.
You can feel differences in top strength which I have noticed effects the perception of stiffness in the strings.
Some classical guitars are so lightly constructed that you can see them moving.
Especially at the instant of attack.
Some of the tops of GJ guitars I've had a look at flex very easily at the rim in the lower bout.
Some not so much.
You can hear and feel stark differences between guitars of the same make and model depending on the top strength variables.
Hear as well as feel.

Jazzaferri

fixed bridge guitars produce most of their sound by the saddle/bridge rocking back and forth in the same plane as the top

moveable bridge guitars produce from motion in a plane perpendicular to the top