Fluorocarbon sting tension

[charles-nix]

Charles- Do you know if anyone has done any tests to see what the tension is on these carbon strings, as compared to gut and nylon? I would love to see a table where nylon, gut, and carbon strings have been tested to see exactly what the tension is for each one on any particular string. Nylons have the lightest tension, and gut has more tension. But how much more? And how “light” for nylons? And do carbon strings have significantly more tension than gut strings? If they do, then this could cause structural problems over the long term for the neck and soundboard.

@carl-swanson Carl, I am quoting your question above, and starting a new topic. I’d like to put out here what I understand. As you know, I came to harps from a physics/chemistry background via a career as a pipe organ builder. And I am positive a lot of this you may know very well already, but I will start with basics in case someone else needs the info and searches the forum. in the future.

To directly answer, no, I don’t know of any tests–at least since the 18th century. Based on work by many previous others, the mathematical relation between length, material density, tension, and pitch was established by lawyer! and mathematician Brooke Taylor in about 1715. Any stringing calculation spreadsheets you may see are based on his work. An absolutely excellent full discussion of using the Taylor equation by Rick Kemper can be found on the Sligo Harps website here, under String Theory: https://www.sligoharps.com/string.html

There have been many later refinements, but they mostly deal with the additional tension caused by pulling to pluck and how that affects the harmonic development of the waves on the vibrating string.

The interesting (and initially non-intuitive) part of this is that a string that is scaled too long, assuming a certain material will break before it reaches pitch no matter how large you make it. Larger diameters result in more breaking strength, but also have more mass, so require more tension to reach pitch, and the percent of max tension remains the same. If a _string_ constantly breaks _due to over tension_ the only solution is re-design the harp or change materials.

In the lever harp world, we don’t have strings selected by note and octave like pedal harps. Nearly everything is directly by material and diameter, and you use a chart to pick the right diameter for the note.

In the pedal harp world, charts of actual string diameter (some with allowable tolerance) are available from all the string manufacturers, but they can be harder to find. The key is that the packaged diameter for a certain note is smaller for fluorocarbon strings than for gut, and different again for nylon. It is not a lot, but fluorocarbon is only about 20% more dense. Since the area is proportional to the square of the diameter, only about a 9% decrease in size is required to maintain the same tension.

So, how closely do the string manufacturers adhere to this? There are other factors: tensile strength of the material, how the prongs will engage, how levers (of all styles) will engage, etc.

Just for example, here is the tension I calculate for 3C, 4C, and 5C for materials currently offered per diameter specs from string manufacturers, on the string lengths measured on a Swanson Empire:

Material                                          Tension (lbs.)
<ul>
                             3C                      4C                    5C                           </ul>

Bow Brand Std Pd            29.8                    41.4                  54.8
Bow Brand Nylon             26.9                    35.0                  53.7
Bow Brand Hvy Pd            32.7                    45.5                  72.5
Savarez KF fluorocarbon     33.0                    46.3                  76.9

So, yes, it seems they give more tension at the recommended stringing diameter. But I wouldn’t say a whole lot. The manufacturing tolerance on BB Std gauge overlaps the Hvy gauge tolerance range, so some strength has to be allowed for that. The fluorocarbon (and rectified nylon) will be basically right on diameter because they are ground to size specs. I had never really looked at the Hvy gauge series before, but it is basically one note heavier than standard gauge from the top down to 4C, then gradually increasing to two notes heavier at 5A.

To me, there is no big special deal about fluorocarbon. It has a couple of properties that might make it useful in certain cases. One, where the harp is mis-designed, or compass is being changed lower, leaving some notes too short. Changing to fluoro can keep those notes brighter. Two, where the harp is designed for it, and one wants an overall brighter sound at a given tension. Three, where tuning stability is paramount. Nylon absorbs 10% of its weight in moisture from the air, which is why it goes out of tune: it is simply, suddenly, 10% more massive. Gut doesn’t absorb moisture as quickly, though it gets weak in moist conditions and breaks easily. Fluorocarbon basically absorbs zero water. Take it from a dry room to rain outside, and the tuning will barely budge–until the wood moves after hours to days later.

Fluorocarbon has one big downside, at least for when new strings are installed. It stretches for-e-e-e-ver. If I restring something in fluoro, I plan on daily tuning for a month before it begins to stabilize.

• This topic was modified 2 months ago by charles-nix.
• This topic was modified 2 months ago by Harp Column Staff.

[balfour-knight]

This is good, Charles. I appreciate all your knowledge on this subject. However, I’ve never been fond of Fluorocarbon strings because they always feel rough and hard to my fingers, and they take so long to hold pitch. A friend of mine had a Camac lever harp, and I used to do all the maintenance on it. The carbon strings were expensive and hard to deal with, in my opinion. Also, since Camac harps are already delightfully bright, like my pedal harp, the carbon strings made that lever harp too bright, in my opinion! If it had been my harp, I would have investigated restringing with lever gut or nylon.

Hope Carl enjoys all this information.

Best wishes,
Balfour

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