Course Pair Tension Calculator

Snap! A quick little ping and a string just snapped mid strum. If you have ever plucked away at a twelve string, played a bouzaki or mandolin, this sound is enough to scare the socks off you. But what do we do now? Why did this string break and not it’s partner? The answer lies in math.

It asks how much tension a line can support over a given distance. On a pair of strings sharing the same space, when they are running parallel to each other, one will snap and hold on tight to next. It’s almost never random. Although it appears as such, it really isn’t.

Why Strings Break

It doesn’t matter how well you pick or which picks you prefer; the physics dont give a damn about any of it. It’s all about mass, frequency, and scale length. On a standard mandolin, distance from bridge to nut isn’t far, so it maintain reasonable amounts of tension even when tuned high. But that same gauge on a longer scale will quickly increase in tension.

By entering the details of your set-up, the calculator does heavy lifting for you. No need to remember some formula with gravity constants and unit weight. All you have to know is this: longer = lighter if you want to be good to the neck.

That’s all well and good for the two strings that make up a pair. It gets interesting when you consider how they relate to one another. On a mandolin unison pairs of string are simple; they’re paired and both strings vibrates on the same note. And if you use the same gauge, then they pull equally hard.

It’s a different story on a twelve-string guitar with octave pairs. Because one of the strings is vibrating at double the speed (the octave), that alter the equation. In order for the pair of strings to play evenly without feeling like one is slack and the other taut, the octave partner need to be significantly thinner. You can’t really match gauges on an octave pair and expect it to work unless you want the upper string breaking off instantly or sounding dead and lifeless.

Most folks make set swapping errors. They glance over a set of gauges in a catalog, conclude the thicker sound better, and then think nothing of the added stress it will put on their instruments’ bridge and tailpiece. Remember, there is almost three-hundred pounds of total tension across all six courses on a 12-string guitar. That’s enough mass to dent soft woods if not controlled.

If you use heavier strings to get more depth or volume, they can puts too much stress on a vintage guitar top. It isn’t about loudness, but rather maintaining the integrity of your instrument.

It also understands materials. Casual players may not realize that different types of strings behaves differently. Wound strings aren’t made the same as plain steel ones because of their density and construction. They’re constructed and more denser. So a wound bass string should of been tuned to a higher pitch than a plain steel octave string with the exact same tension.

The unit weight takes into account these material variations and automatically adjusts based off those differences. No need to figure out the relative density of nickel wrap vs phosphor bronze yourself. Just tell it what kind of strings you intend to purchase. The math will adjust to match how that particular metal vibrates and stretches given the tuning you’ve selected.

The feeling of the instrument can be affected slightly by tuning changes as well. Many players prefer to have some shimmer to their instruments which comes from intentional chorus spreads and small amounts of cent offsets. Although having a few cents off won’t make much difference in total tension load, it does impact the way the pair work together on sustain. You may find that a slightly loose string starts to flutter against the neighboring string. This causes a buzz that sounds like an error but is realy just bad balance.

Balancing the percent on the pair gives you an idea if they’ll be singing or fighting each other for dominance in the mix. A paired-course instrument is a dance with compromises. Tension should be high enough to provide stable intonation and clear articulation without being excessive and causing fret-out issues or structural damage. Perfection isn’t the objective of any single digit. Harmony is what’s desired throughout the set.

Once you get it through your head how one string broke when its partner didn’t, then you quit complaining about luck and look at the relationship between pitch, gauge, and scale instead. That mental switch makes what was once a frustrating repair session become a workable setup routine. You will spend less time fixing broken strings and more time playing them all together in tune until the song is over.