Tension of a string on 660 vs 650

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Tension of a string on 660 vs 650

Post by Ramon Amira » Thu Apr 06, 2017 4:34 pm

I was just having a discussion with someone about the tension on a string with a 660 vs a 650. I thought that since it takes more tension to bring a longer string to the same pitch that the 660 would feel as though it had higher tension than a 650.

He felt exactly the opposite. He thought that the longer the string the less pressure it would take to deflect the string, and so it would feel as though it had lower tension than a 650.

I just received an email from him:

"I did some calculations using a simplified model. A full model that considers string material, fret location, etc is very complicated. But, from what I can tell from my simple analysis, the difference in force required to press a fret between 650 and 660 scale is approximately 1/100th of 1 percent. So, irrelevant."

Anyone have any thoughts on this?

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Re: Tension of a string on 660 vs 650

Post by guitarrista » Thu Apr 06, 2017 5:06 pm

I don't know how it would feel, but objectively the same string tuned to the same pitch will have higher tension for 660 than for 650 scale. The tension increase is just over 3% (*). For comparison, 4% is roughly the increase on tension you get when switching one step up in D'Addario strings tension (i.e. Normal to Hard, or Hard to Extra Hard).

(*) Tension is proportional to the square of the scale length, so the tension increase comes from the squared ratio of scale lengths. In this case (660/650)^2 which is 1.031... i.e. just over 3% increase for the tension at 660mm compared to the tension at 650mm.
Last edited by guitarrista on Thu Apr 06, 2017 5:13 pm, edited 4 times in total.
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Re: Tension of a string on 660 vs 650

Post by ChristianSchwengeler » Thu Apr 06, 2017 5:09 pm

For longer scales you need lower tension strings to achieve the same tension as on a shorter scale - and on shorter scale guitars you need higher tension for the same reference tension.
I had just today a junior 3/4 instrument in my workshop for fret leveling. It was 600 mm scale and from the sound I would guess it was just stringed up with regular 650 strings. The trebles do sound realy like plastic and you just can't get enough tension with normal strings on a 600mm scale. Well for chidren it might be a vantage to have very low tension to reduce the effort for the left hand but soundwise not really interessting

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Re: Tension of a string on 660 vs 650

Post by Cloth Ears » Thu Apr 06, 2017 5:37 pm

I have 655mm and 660mm Vicente Carrillo blancas, and the 660mm is noticeably tighter on the fingers. I have a feeling I am not comparing like for like as one is like his 'Paco' guitars and the other is a top end 'Pasion' model which is cross braced and just a better guitar. I think the other important dimensions may be different. The action is certainly lower on the 655mm 'Pasion'.

The 660mm is still for sale in the UK! It is a great flamenco blanca for its resale price, just not the exceptional guitar that the other one is.

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Re: Tension of a string on 660 vs 650

Post by celestemcc » Thu Apr 06, 2017 5:47 pm

I have a 664 and a 640. The tension difference (same strings) is very noticeable, much softer on the 640.
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Re: Tension of a string on 660 vs 650

Post by Ramon Amira » Thu Apr 06, 2017 5:58 pm

celestemcc wrote:I have a 664 and a 640. The tension difference (same strings) is very noticeable, much softer on the 640.
Right. The reason this came up in the first place is that I took in a 660 on a trade-in for a new guitar purchase. I have not had occasion to play a 660 for a long time. I put on a new set of my usual strings and when I played the guitar it just felt like the tension was higher. And this is with far less difference than from a 664 to a 640.

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Re: Tension of a string on 660 vs 650

Post by es335 » Thu Apr 06, 2017 6:03 pm

Hi Ramon,
the calculation approach is very simple. The tension of the strings increase with the square of the scale.
The result is app. 3% higher tension going from 650 mm to 660 mm which is definitely noticeable!
Cheers es335

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Re: Tension of a string on 660 vs 650

Post by souldier » Thu Apr 06, 2017 6:03 pm

As stated above, longer scale length = higher tension.

In terms of how the string actually feels, there are various other factors involved. For example, it is quite possible for a set of D'addario EJ45's to feel tighter on a 640 scale guitar than on a 660 scale guitar. In fact I owned a 640 scale guitar that felt stiff even with low tension strings on them, and I could take the same strings and put them on my other 650 scale guitar and the strings would feel very loose.

celestemcc wrote:I have a 664 and a 640. The tension difference (same strings) is very noticeable, much softer on the 640.
I suspect what you're feeling may not be due to the scale length but due to how the guitar is constructed.
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Re: Tension of a string on 660 vs 650

Post by rojarosguitar » Thu Apr 06, 2017 6:18 pm

When in doubt, just take Arto's String calculator and chose a density and string diameter and a tone, then play with scale lengths ...

e.g. 440Hz pitch e' = 329.63 Hz 0.6 fluorocarbon string: 9.479kg at 650mm scale length and 9.773kg at 660mm scale length and that is a increase of 3.1% (calculation: (9.773-9.479)/9.479*100%)

Another issue is, how increase of string tension translates into the increase of lateral force needed to press the string down...
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Re: Tension of a string on 660 vs 650

Post by bacsidoan » Thu Apr 06, 2017 6:39 pm

May I remind you all that under the same tension, it takes less force to create the same deflection distance on a longer string. If you don't believe me, tie a weight to a string, you will see that it takes more tension to keep a longer string straight. Because of the two opposing effects, it is not necessarily true that a guitar with longer scale always feel tighter, assuming that that the same string is used and the guitars are tuned to the same pitch. A lot of other factors come in to play :)

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Re: Tension of a string on 660 vs 650

Post by celestemcc » Thu Apr 06, 2017 6:57 pm

I suspect what you're feeling may not be due to the scale length but due to how the guitar is constructed.
Entirely true; but this is my experience... and I do concede that my two guitars have many more differences than scale length!
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Re: Tension of a string on 660 vs 650

Post by Ramon Amira » Thu Apr 06, 2017 7:06 pm

bacsidoan wrote:May I remind you all that under the same tension, it takes less force to create the same deflection distance on a longer string. If you don't believe me, tie a weight to a string, you will see that it takes more tension to keep a longer string straight. Because of the two opposing effects, it is not necessarily true that a guitar with longer scale always feel tighter, assuming that that the same string is used and the guitars are tuned to the same pitch. A lot of other factors come in to play :)
This was exactly the argument of my friend. So both aspects seem correct, and I begin to think that they might counterbalance at least to some degree.

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Re: Tension of a string on 660 vs 650

Post by rinneby » Thu Apr 06, 2017 8:15 pm

My Yamaha GC3D has 658mm scale and it feels like the strings have "less tension" compared to many of my 650mm guitars. It's lightly built. I had a Kohno No.30 with 660 scale that felt pretty "hard" to play. Wonderful sound though. I guess its a matter of construction, as well as the thickness of the top.

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Last edited by rinneby on Thu Apr 06, 2017 8:30 pm, edited 3 times in total.
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Re: Tension of a string on 660 vs 650

Post by guitarrista » Thu Apr 06, 2017 8:23 pm

bacsidoan wrote:May I remind you all that under the same tension, it takes less force to create the same deflection distance on a longer string.
But what matters here is whether you are plucking at the same distance from one end or not (if it is the same, then the angle of displacement would be the same, so same effort to displace). If you are plucking at about the same distance from the bridge on the 660 vs. 650 guitar, you would mostly feel the increased tension on the 660 as the contribution to the restoring force from the string displacement would be about the same or small compared to the increase in string tension from the scale increase.

I suppose if I am right, then fretting at fret 1 would feel more difficult (rather than less) on a 660 than on a 650 as fretting is a displacement, and the distance from the nut is about the same, so you would mostly feel the increased tension from the scale increase.

To throw in another possible factor: The feel of tension when pushing (displacing) the string could also be one of more effort when the string is thinner (for the same tension) - as it digs more into the finger?
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Re: Tension of a string on 660 vs 650

Post by mikfik » Fri Apr 07, 2017 11:05 pm

I think everybody is missing the point of using a longer scale length and the benefits one can get with using it. The longer the scale length used- the thinner the string can be for a given tension. A thinner string that has less mass will exhibit less stiffness and thus more flexibility.
So we end up with equal tension but a more flexible string that is less en-harmonic and thus sounds better and feels better to both hands. Try it,you'll like it.

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