Gut strings tension calculator

Edited: December 30, 2018, 4:27 PM · Hi, I discovered Gamut website, and they have a great string calculator:

I play a 16.5 inch viola with 38cm vibrating string length.

I want to tune it E4 A3 D3 G2 or B4 E4 A3 D3, but I dont know which tension in Kg to choose in the calculator to get the right diameter.

Help me please!

Replies (12)

December 30, 2018, 4:41 PM · It looks to me as though it does not do what you want - that is give a string diameter for a string less than 60 cm long for a 220 Hz A.
Edited: December 30, 2018, 8:50 PM · It seems there may have been a typo or two in the OP's post, in which case he could have intended E4 A4 D3 G2 (violin tuning), B5 E4 A4 D3, or even B4 E3 A3 D2 (a possible cello gut tuning which would hardly be successful on a viola). It appears according to Andrew that A3 (and D2) are not calculable for that viola setup, so presumably are not considered technically feasible in gut, at present.

Or perhaps the OP did not make any typos but is in fact considering tunings that could be used in his Arab Andalusian style - I am speculating here because I am not familiar with that music genre. In any event the A3 does not appear to be possible in gut at the moment.

December 30, 2018, 8:54 PM · You'll need wound gut. I'd email Dan Larson. Gamut's real nice about answering questions.
December 31, 2018, 4:09 AM · @Andrew & Trevor: It's difficult because you have to know the correct tension to get the right diameter, this is not a standard tuning!

@Cotton: B4/E4/A3 can be plain gut also...

Edited: December 31, 2018, 4:53 AM · My understanding of the question may be faulty, but from what I can recall of looking at guitars and ukes 5 years ago, the exact tension isn't so important. I can see from the calculator that the total tension for a viola is about 20Kg, so just allow 5kg per string. The main changes in tension will come from scale length, frequency, string material density and string diameter.

Yes, in fact what you need is a table that lets you change frequency. The tension isn't the problem.

Tension is proportional to
D x f squared x l squared x d squared
where D = density, d = diameter
Which is convenient - it just means f and d are inversely proportional for constant tension.

In other words, go to the default table, put in 38cm, leave the tensions as they are, and then calculate reduced diameters proportional to the raises in frequency.

Thanks to Pythagoras, we know that up a fifth is 3/2, so the strings need to be 2/3 the diameter for the same tension, and up a fourth is 4/3, so the strings need to be 3/4 and so on. You can do others by interpolation - exact calculations won't be necessary. The small changes in tension that will result from small inaccuracy are of no importance.

December 31, 2018, 5:11 AM · 20kg is just a default exemple, not a standard for viola!
Edited: December 31, 2018, 5:32 AM · It's their suggested default. It's towards the lower end of their suggested range, and I think it's reasonable. If you don't like it, you could choose 7, which is in the middle of their suggested range, but better to be safer with lower tension. Standard for Classical Guitar is 90-100LB or 40-45KG divided between 6 strings and with greater scale length, so the calculator seems sensible to me.

Like Cotton says, EMail Gamut if you are in doubt.

Edited: December 31, 2018, 5:59 AM · @Amine, it occurs to me that if a viola G2 is tuned up a tone then you get A3, a tuning you want. Tuning a low tension gut lower string of a viola up a tone shouldn't be a problem. I think it is worth trying.

This sort of scordatura tuning is not uncommon in some genres of folk fiddling, and that today would be with synthetic or steel strings. I've done it myself in the past by tuning a violin synthetic G up a tone so give the added resonance of a 4th interval drone with the open D. Scordatura was also used on the violin in the Baroque era (with gut strings) – see Biber's “Mystery” sonatas for outstanding examples in which the scordatura sonatas would not be properly playable in normal tuning.

December 31, 2018, 12:41 PM · Part of the challenge here is the fact that the acceptable range of string tension varies according to the frequency of the open string tuning.

For example, a string tuned to A4 (440hz) typically comes in tension ranges from around 5kg (light) to 6.5kg (heavy).

While a viola C3 (131hz) more typically comes in a tension range from 3.5kg to 5.0kg.

A G2 open tuning is 98hz. That is well below any published viola string I've seen, so one cannot be sure what tension range will give a reasonable sounding and responsive string that is not excessively thick.

For D3 A3 E4 B4 you can use the calculator for C3 G3 D4 A4 with the default tensions, then reduce the diameter it gives in proportion to the frequencies.


D3 is a step up from C3. C3 frequency of 130.81hz and a default tension of 5kg gives a 2.2mm diameter. D3 is 146.83hz. So its diameter would be:

(130.81/146.83) x 2.2 = 1.96mm

Notice how thick a pure gut C3 or D3 string needs to be. That's why these usually come with some metallic sheathing so the diameter can be decreased.

Edited: December 31, 2018, 2:20 PM · Arto's string calculator might be useful:

Also you may find that Gamut doesn't do pure gut as thick as some others. If they don't have what you need (and do email them), check with the various European suppliers: Aquila (has a US distributor), Toro, Pure Corde (these are made in Morocco I believe), or George Stoppani's Pure Gut project. Do your own research as to quality, I have had good product from Gamut, Stoppani, and Aquila but do not know the others firsthand.

January 1, 2019, 7:39 AM · @Andres: same problem, you must know the right tension to calculate
Edited: January 1, 2019, 8:21 AM · There are three things you can do, Amine.

1. Trial and error. Choose a tension in the middle of the range. Try the resulting string. Decide if you want it tenser or less tense.

2. Look at page 17 of this: -
(except that's for violins, so you'll either have to Google for a viola version or extrapolate)

3. Buy a micrometer and measure your current string diameters, unless it says what they are on the packet. Calculate their tension. Calculate new diameters for new frequencies at same tension.

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