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String tension on multi-scale instruments?

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String tension on multi-scale instruments?

Postby Doug Shaker » Mon Jan 16, 2017 3:24 pm

I am working on a multi-scale baritone, and I wondering how much tension other builders like to design into their instruments. I had been assuming about 20 lbs. per string, but have seen some estimates by other builders that make me believe that they are designing to something more like 30 lbs per string.

Any ideas, heuristics, prejudices?
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Re: String tension on multi-scale instruments?

Postby Brian Evans » Mon Jan 16, 2017 4:02 pm

To me it depends on a few factors, but I would think most acoustic guitars are in the 150 - 180 lbs range for six strings, so 25 - 30 lbs per string. What I have observed is that if you get under around 25 pounds the string starts to get floppy and has intonation problems, pitch varies more with bending, that sort of thing. Never really played with it that much mind you. A long scale bass string on a baritone guitar would be closer to a bass string, and some of them have quite high tension.
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Re: String tension on multi-scale instruments?

Postby Doug Shaker » Tue Jan 17, 2017 3:49 pm

I took a look at the data on Elixir Nanowebs and they have a section on their web page:
http://www.elixirstrings.com/guitar-strings/80-20-bronze-guitar-strings.html
that lists "String tension for tuning". The tension that they list varies by string (no surprise there) and goes from 24 to 35 pounds per string for a medium gauge string set. For extra lights, they go as low as 16 pounds for a string. For heavy strings on a 12-string or a baritone, they get as high as 47 pounds for a single string. Yikes!
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Re: String tension on multi-scale instruments?

Postby Doug Shaker » Tue Jan 17, 2017 7:13 pm

OK, here's what I did. I found out what strings my customer likes to use on his current guitar. I then figured out what string tension there was on each string for the tuning, string weight and scale length for his current guitar. Then I used the D'Addario string database to figure out what strings would give the same tension on each individual string on the baritone in the tuning that I have planned for the guitar. If you are interested, the scale lengths and string weights are:
    # Scale Note String
    1. 685mm B3 0.016
    2. 693mm F#3 0.022
    3. 701mm D3 0.032
    4. 709mm A2 0.042
    5. 717mm E2 0.056
    6. 725mm B1 0.059
This baritone is tuned down a fifth from standard.

Does anyone know of any string suppliers that will let me spec a custom string set and then let that specification be available to my customer in the future?
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Re: String tension on multi-scale instruments?

Postby Barry Daniels » Tue Jan 17, 2017 9:01 pm

I Googled "build your own string set" and got a bunch of promising hits.
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Re: String tension on multi-scale instruments?

Postby Brian Evans » Wed Jan 18, 2017 7:56 am

Some Dobro/resonator sets are .016 - .059, so they might work. I would expect that string length will be an issue with those, though. Why not just try an off-the-shelf baritone set, .013 - .062? Tons of those available.

edit: here is an interesting post, and some interesting comments on the bottom as well. Now off to research "inharmonicity". http://www.haloguitars.com/store/blog/t ... e-guitars/
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Re: String tension on multi-scale instruments?

Postby Brian Evans » Wed Jan 18, 2017 8:54 am

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Re: String tension on multi-scale instruments?

Postby Alan Carruth » Sun Jan 22, 2017 6:25 pm

I should have thought of this earlier.

Harp makers pay attention to the ratio of tension to length of the strings. This is what determines the 'feel' or 'compliance' (what some folks mistakenly call the 'tension') of the strings. If they're to slack it's hard to play well with the right hand, and to tight, of course, affects the left hand. In addition it's important that the T/L ratio should be pretty similar across the set, and especially important that it doesn't change suddenly from one string to the next. The rule of thumb on harps is to have about 1# of tension per inch of length. Guitars tend to come in lower than that, say around .7#/in., iirc. Using this sort of rule allows you to at least come up with some sort of number for the tension on each string. Then you can look up what's available and figure out which strings will come close. You could look at the T/L for normal strings, and the amount of variation that is common, to get an idea of the 'right' ranges.

Another thing harp makers look at is the 'characteristic impedance' (Z) of the strings. This is simply sqrt(Tension*mass). It's a measure of how hard it is to get the string going, and also how hard it will push on the bridge at a given amplitude. Once again, the more equal that is between the strings in a set, the more 'even' they're likely to be, in this case, in terms or their power.

It is sometimes said having equal tension on all the strings is desirable, but T/L and Z negate that to some extent. Ideally having each of them equal across the set would be wonderful, but in reality you usually can't get that. The art of setting up strings is knowing how to compromise.
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Re: String tension on multi-scale instruments?

Postby Beate Ritzert » Sun Jan 22, 2017 9:29 pm

May i ask something else regarding multiscale?

[quote="Doug Shaker"]
    # Scale Note String
    1. 685mm B3 0.016
    ...
    6. 725mm B1 0.059

40 mm on a 6 string. Quite a lot?

Quite recently i have searched on the net on hints on designing a multi-scale layouts out just in order to improve ergonomics. Target is a Bass VI, i.E. E1-E3 on 30" scale length, first experiments point toward a difference of 30 mm and a common point around fret 7 or 8. Which appears to me pretty much... (i would like to avoid having to order custom strings and use standard sets designed for the bass VI or preferably, the Hellcat VI, e.g. the LaBella flat wounds)
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Re: String tension on multi-scale instruments?

Postby Doug Shaker » Mon Jan 23, 2017 2:59 pm

Correction: I had said

Doug Shaker wrote: If you are interested, the scale lengths and string weights are:
    # Scale Note String
    1. 685mm B3 0.016
    2. 693mm F#3 0.022
    3. 701mm D3 0.032
    4. 709mm A2 0.042
    5. 717mm E2 0.056
    6. 725mm B1 0.059 Should be more like 0.070
This baritone is tuned down a fifth from standard.

My string-weight spreadsheet picks a string from a database of D'Addario strings and I found out that that the value for my 6th string was being distorted by the limits of the strings in my database. The sixth string should be more like a 0.070.
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Re: String tension on multi-scale instruments?

Postby Doug Shaker » Mon Jan 23, 2017 3:08 pm

Beate Ritzert wrote:May i ask something else regarding multiscale?

Doug Shaker wrote:
    # Scale Note String
    1. 685mm B3 0.016
    ...
    6. 725mm B1 0.059

40 mm on a 6 string. Quite a lot?

Quite recently i have searched on the net on hints on designing a multi-scale layouts out just in order to improve ergonomics. Target is a Bass VI, i.E. E1-E3 on 30" scale length, first experiments point toward a difference of 30 mm and a common point around fret 7 or 8. Which appears to me pretty much... (i would like to avoid having to order custom strings and use standard sets designed for the bass VI or preferably, the Hellcat VI, e.g. the LaBella flat wounds)


I think that whether a 40mm difference in scales is a lot depends on your player and how the frets are laid out. When you design the fretboard, you will need to pick a fret to be perpendicular to the string direction. In my case, I think (I'm at work and can't look at my plans) I made the 9th fret be perpendicular fret. That puts the "frets" that are most distorted from perpendicular down below, between the end of the fretboard and the bridge, where they don't matter.

A maker whose work I respect a LOT, Tony Yamamoto of San Francisco, has three different multi-scale designs and the scale differences range between 34mm and 40mm.
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Re: String tension on multi-scale instruments?

Postby Jason Rodgers » Mon Jan 23, 2017 3:55 pm

Any particular reason you chose 685mm treble to 725mm bass for your scales (about 27" to 28-1/2" for us metrically challenged)? A 1-1/2" scale difference isn't a big deal, especially considering the Novax Charlie Hunter model has a splay of about 3". I bet you could get away with both sides being 1/2" shorter, so about 673mm to 711mm (26-1/2" to 28").

When it comes to choosing where to put the perpendicular fret, the 7th or 9th has sort of become a "standard," but the decision needs to include how much the player uses those upper frets, which you accurately described as becoming more distorted up the neck. I built a 7-string with 25-1/2" to 27" scales and put the perpendicular fret at the 7th. In my experience, the fret splay in first position wasn't a challenge to adapt to, but playing up around the 17th fret resulted in some problems. As the bass side tips over the treble, and the treble fret edges are effectively "behind," there are some visual as well as physical issues as fingers tend to pile up. I thought I had stumbled upon a major drawback of the multi-scale design, until I saw this blog post by Ola Strandberg (you can see my comment, too) http://guitarworks.thestrandbergs.com/2 ... d-markers/ On all subsequent guitars - 6-, 7-, and 8-string - I'm putting the perpendicular fret at the 12th.

And that doesn't look like a weird, custom set you've listed. It looks like a 7-string set with the highest string tossed out. For my 7-string, I bought a D'Addario XL 8-string light set and tossed the highest string, so it feels like an 11 set with a low A.
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Re: String tension on multi-scale instruments?

Postby Doug Shaker » Mon Jan 23, 2017 7:26 pm

Jason Rodgers wrote:Any particular reason you chose 685mm treble to 725mm bass for your scales (about 27" to 28-1/2" for us metrically challenged)? A 1-1/2" scale difference isn't a big deal, especially considering the Novax Charlie Hunter model has a splay of about 3". I bet you could get away with both sides being 1/2" shorter, so about 673mm to 711mm (26-1/2" to 28").


Yes, I think I could have gotten away with a shorter set of scales, but the player I am building this for wanted a "big guitar" sound, so I am building a GS-sized body. After I got the body size down and I needed some longer scales to put the bridge where I wanted it. Who knows, it could be a bust, but so far, the build looks and sounds good and I'm encouraged.
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Re: String tension on multi-scale instruments?

Postby Doug Shaker » Mon Jan 23, 2017 7:29 pm

Alan Carruth wrote:I should have thought of this earlier.

Harp makers pay attention to the ratio of tension to length of the strings. This is what determines the 'feel' or 'compliance' (what some folks mistakenly call the 'tension') of the strings. If they're to slack it's hard to play well with the right hand, and to tight, of course, affects the left hand. In addition it's important that the T/L ratio should be pretty similar across the set, and especially important that it doesn't change suddenly from one string to the next. The rule of thumb on harps is to have about 1# of tension per inch of length. Guitars tend to come in lower than that, say around .7#/in., iirc. Using this sort of rule allows you to at least come up with some sort of number for the tension on each string. Then you can look up what's available and figure out which strings will come close. You could look at the T/L for normal strings, and the amount of variation that is common, to get an idea of the 'right' ranges.

Another thing harp makers look at is the 'characteristic impedance' (Z) of the strings. This is simply sqrt(Tension*mass). It's a measure of how hard it is to get the string going, and also how hard it will push on the bridge at a given amplitude. Once again, the more equal that is between the strings in a set, the more 'even' they're likely to be, in this case, in terms or their power.

It is sometimes said having equal tension on all the strings is desirable, but T/L and Z negate that to some extent. Ideally having each of them equal across the set would be wonderful, but in reality you usually can't get that. The art of setting up strings is knowing how to compromise.


Thanks for the, as always, carefully thought-out, generous and informative response. I will take a look at my string choices in the light of your more detailed heuristic. I had been thinking, "Same tension! Good!" but I will take a look at the 0.7# per inch guideline and see if that leads me to different choices.
Thanks!
-Doug Shaker
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Re: String tension on multi-scale instruments?

Postby Doug Shaker » Mon Jan 23, 2017 8:44 pm

Alan Carruth wrote:
The rule of thumb on harps is to have about 1# of tension per inch of length. Guitars tend to come in lower than that, say around .7#/in., iirc. Using this sort of rule allows you to at least come up with some sort of number for the tension on each string.


Actually, it looks like the steel-string guitars in my stable come up at more like 1#/in. 0.7#/inch might be where nylon strings end up, though.

If I recalculate the target string tensions based on 1#/in, I get target tensions for my scale length that range from about 29 pounds for the 1st string to 31.4 pounds for the 6th string.
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Re: String tension on multi-scale instruments?

Postby Doug Shaker » Tue Jan 24, 2017 4:40 pm

Reworking my string tensions and string weights, using a target tension of about a pound per inch in scale length, I get the following:
# Scale Note Tension String
1. 685mm B3 29.7# 0.017 in, plain
2. 693mm F#3 30.0# 0.022 in, plain
3. 701mm D3 30.4# 0.030 in, wound
4. 709mm A2 30.7# 0.039 in, wound
5. 717mm E2 31.1# 0.053 in, wound
6. 725mm B1 31.4# 0.071 in, wound
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Re: String tension on multi-scale instruments?

Postby Alan Carruth » Wed Jan 25, 2017 1:32 pm

Sounds OK. If you want to use a smaller low E reduce the size of the A as well so that the T/l changes more or less smoothly.
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Re: String tension on multi-scale instruments?

Postby Jason Rodgers » Thu Jan 26, 2017 12:53 am

I read back through the thread but didn't see any references to the D'Addario String Tension Pro calculator. It does what you've been figuring. I've played around with attempting to assemble even tension sets for different multi-scale arrangements, and found that you can't actually get a perfectly even set across the strings. This makes sense, of course, because the string companies only make so many gauges, and you're essentially attempting to match them with arbitrary lengths and pitches. It becomes especially challenging on the wound/unwound boarder, where going one way or the other can result in the biggest jumps in tension.

I understand what you're attempting, Doug, with one particular customer and one particular build, but in the big picture of players and their choices about string tension and feel, I don't know how useful/necessary it is to attempt even tension: after all, the string manufacturers make standard sets from light to heavy, then combos of light top with heavy bottom, heavy top light bottom, etc. People will adjust to taste and find what they like.
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