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Scale length:String tension - actaully related?
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=31266		 Page 1 of 1
Author:  cactus [ Fri Feb 25, 2011 2:28 pm ]
Post subject:  Scale length:String tension - actaully related?
May've just had my mind blown..

My physics friend is trying to shatter my understanding that string tension is related to scale length. He says that the string length is responsible, not where the string is fretted (the nut being the last fret). He says that the entire stretched portion of string (from ball end to where the string enters the post) determines the tension. Are we altering TENSION when we use a capo? Is tension sepaprable from pitch?

Can a short scale and looong headstock and have same string tension as a longer scale and short headstock?

I remember reading that BB King consumed the entire string in a wad around the tuning post - not cutting any of it. Would this not then be the maximum tension allowable by that string regardless of scale length?
Author:  John Arnold [ Fri Feb 25, 2011 2:35 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
Your physics friend needs to go back to class....and study the string equation. It is the vibrating length of the string that determines the tension. The string is considered to be fixed at the nut and saddle, and you can prove it with a locking nut. Lock the strings, and the pitch does not change.
It can be argued that a longer string length past the nut can alter the feel of the guitar, particularly when bending the strings. But in that case, the strings feel looser, not tighter.
Author:  My Dog Bob [ Fri Feb 25, 2011 2:35 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
In a GAL article Bob Benedetto had some experiments where he altered the length of the string behind the bridge from one extreme to the next and then had a bunch of luthiers/musicians try to tell the difference. They couldn't tell. They all said it felt the same.

I'm not saying anything by this, it's just what was posted in the article..

Regards, Peter Z
Author:  cactus [ Fri Feb 25, 2011 4:21 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
So the tension changes when i add the capo? That doesnt work in my head..but most things dont. ;) I'll slide the capo around and see if i notice a change in feel.

Thanks for the input.
Author:  TonyKarol [ Fri Feb 25, 2011 6:23 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
Really ??? Come on .... It is NOT the vibrating length that determines tension .. the tension is the same over the entire length of the string, from ball end to tuner post (explain to me how it could be any different ??). It FEELS tighter from the nut to the tuner because the length there is short - but its the same tension as the string on the neck. So, your friend is correct on that point.

The vibrating portion of the string between the saddle and the nut (or fret), at a given tension, for a given gauge of string, determines pitch. Making a longer headstock for a guitar with the same scale as one with a short one - the tension at pitch is the same !!! Putting a capo on does not alter tension (OK, maybe one thats too tight and stretches the string to the FB and casues it to go sharp does .. but a good one wont), niehter does fretting a note .. you are altering speaking length, thus changing pitch.
Author:  yukonarizona [ Fri Feb 25, 2011 7:58 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
I agree with Tony here, but I do believe that applying a capo changes the working tension of the string. The string must experience greater tension when held to the frets in two separate positions.
I've often wondered how to judge the effect of break angle on string length/tension. At some angle the string beyond the break must cease to be part of the working length.
Gotta split. More thoughts later.
Author:  bluescreek [ Fri Feb 25, 2011 8:03 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
Capoing does in fact change tension but Tony is right the rest of the way
Author:  David Newton [ Fri Feb 25, 2011 8:37 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
The OP mentioned tension and scale length, but no one has said, unless I've missed it, that string tension on a short scale guitar is lower at pitch than a long scale guitar. Maybe that is what your physics friend was getting at.

As far as a capo raising tension, yes to the same degree that finger fretting raises tension, really, not much.
Author:  bluescreek [ Fri Feb 25, 2011 9:16 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
that is a fact , the shorter the scale the less the tension on the same gauge string
Author:  the Padma [ Fri Feb 25, 2011 9:32 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
cactus wrote:
...
He says that the entire stretched portion of string (from ball end to where the string enters the post) determines the tension. Are we altering TENSION when we use a capo? Is tension sepaprable from pitch?



Tension is the amt of yank you got on the string. ~ How tight you got it tuned up to. How hard you trying to get the ends of the string away from each other. Pull baby pull.

Capo does not alter the yank.


As you increase the yank, (tighten the string) the pitch will go up. Chanaging tension changes the pitch. Simple eh!






cactus wrote:


Can a short scale and looong headstock and have same string tension as a longer scale and short headstock?


Yes they can depending on the sting guages. Remember, tension is determined by how hard you be yankin on that string (tighteningh it by tunning it up.)

How ever the compliance will be different and so the strings will feel more compliant, on the longer headstock instrument.

Compliance and tension are two different animals. But most refer to both as tension and don't know what they babble about. See Al Caruths rant on compliance some where on this here site.



cactus wrote:
May've just had my mind blown..

I remember reading that BB King consumed the entire string in a wad around the tuning post - not cutting any of it. Would this not then be the maximum tension allowable by that string regardless of scale length?



Don't matter how much string is wrapped around the post. However winding up of the slack in the string will cause it to go into tension. Increase tension (tuning it up higher) and the frequency or pitch raises. Keep increasing the tension to the max and guess what...the string breaks...than what?


May me suggest you run a search and study

Tension
Compliance
String length.

But not with you friend.


blessings
duh Padma
Author:  John Arnold [ Sat Feb 26, 2011 1:19 am ]
Post subject:  Re: Scale length:String tension - actaully related?
Quote:
So the tension changes when i add the capo?

Yes. Any time you press the string against the frets, whether with a capo or with your fingers, the tension raises. In fact, the raising of the tension is why there is compensation at the bridge. The frets are placed at the theoretical correct spot, based on the inverse rule....frequency is inversely proportional to the string length. Raising the tension during fretting alters this, and it is not a linear function.
However, the amount that the static tension raises with a capo is very slight. Maybe you are referring to the increased stiffness of a shorter string. That assumes that the capo also fixes the string as rigidly as a nut or saddle.
Author:  Andy Birko [ Sat Feb 26, 2011 7:11 am ]
Post subject:  Re: Scale length:String tension - actaully related?
OK, just about everyone who's posted on this topic is correct to a degree but....we need to just look at the equation:

Tension = unitmass*(2*Length*Frequency)^2

When you fret a string, length and frequency change, but all the other parameters stay the same so tension is "the same".

However because we live in the real world, some reality creeps in, namely compensation. When you fret (or capo) a string, there is indeed a small tension change (increase) due to the displacement of the string. The magnitude of the tension change is dependent on the material properties of the string.

The easiest way to illustrate this is slide guitar. Barely touch the slide just above a fret and you get an immediate pitch change. We clearly haven't changed the tension of the string, just the length and therefore get change in pitch. If you're playing a steel string, you'll also notice that the pitch itself is flat compared to the fretted pitch. Why? because of the compensation at the bridge. If you now take the slide and slowly press it to the fret while picking, you'll hear the pitch rise little by little until you hit the fret at which point it should be right on.

There are fret calculators out there that will calculate the amount of pitch and tension increase due to fretting displacement - the higher the action, the more compensation you'll need.

Clear as mud?
Author:  TonyKarol [ Sat Feb 26, 2011 9:29 am ]
Post subject:  Re: Scale length:String tension - actaully related?
OK then .. yes, the tension changes are miniscule when fretting or capoing .... we are talking a few cents change in pitch here.
Author:  Stuart Gort [ Sat Feb 26, 2011 2:30 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
Fretting a note increases string tension on a minscule level...but enough to consider using stretch compensation when calculating fret placement. Adding capo shouldn't add any significant amount of tension to the strings from the standpoint of playability.

When two strings of identical mass (same alloy and gauge) but different lengths are tuned to the same note, the string with a longer length will have more tension. I like a shorter scale length for this reason....easier on the hands.

If a string has x tension on it...it has x tension for the entire length for the string...up to the hard points. On a guitar the hard points are the tuner pegs and whatever restrains the endball.

Now...someone check me on this. A longer scale length should sustain a tad longer....due to more mass?
Author:  TonyKarol [ Sat Feb 26, 2011 4:00 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
I wil tell you this Zlurgh .. if you tune the low E string on the guitar neck of my harp to D, at .056 gauge and 25.5 inches, then compare that to the open harp string D at about 29 or 30 inches and .054 ... no comparison, the harp string rings forever ... and sounds better too.
Author:  Andy Birko [ Sat Feb 26, 2011 4:14 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
I can back up Tony. Longest treble string on my banduras is 18" tuned to an e below middle c and it's around .040 iirc. Rings way longer than a guitar.
Author:  mhammond [ Sat Feb 26, 2011 6:42 pm ]
Post subject:  Re: Scale length:String tension - actaully related?
Isn't this about the 15th time we've had this argument?

[uncle] [uncle] [uncle] [uncle] [uncle] [uncle]

Mikey
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