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Thread: String sizing and tension for an OM

  1. #1
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    Default String sizing and tension for an OM

    I have built a couple of 22" scale length GOM's and am wondering what the ideal string sizes for these instruments would be. I am currently using .011, .016, .028 and .044. the string calculator for these strings gives 133psi. to properly balance all strings I should go to .012 and .017 for the higher strings according to the calculator. the break angle at the bridge is 14 degrees. This all seems to work, but I am not sure if it would be too much or too little for this scale instrument. It is tuned G D A E.
    Bob Schmidt

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    Default Re: String sizing and tension for an OM

    Perhaps putting this another way, is there a general rule of thumb for total tension vs scale length. The other thing I measured was the top deflection tuned to pitch, and that was .014".
    Bob Schmidt

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    Default Re: String sizing and tension for an OM

    Is there a reason you are going with solid strings for the second course? Most OM’s use wound strings there. I believe D’Addario’s J80 set would be good for your scale length. Those are .012, .022w, .032w, .046w. It is my belief that balanced tension across the bridge is important for consistent tone. It’s usually impossible to get them absolutely equal but I like no lower than 20 pounds per string and no more than 23. The above set fits the bill but the E course is a little light at 17 pounds. I might go up to .013 there. That would give us total tension of around 166 pounds give or take. I think any properly constructed instrument should be able to handle that easily.
    Don

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    Default Re: String sizing and tension for an OM

    Thanks Don. I tried a couple of different size wound strings on my 26" bouzouki. The thickest I tried was .020, and when I could bring them to A without breaking I did not like the sound as much as the plain steel, but of coarse that is a different instrument.
    This tells me I am not over stressing the instrument which was my main concern. If I raise the the E and A strings to .012 and .017 It would ballance them at around 18lbs each and 149 total. It looks like I am a bit light then. I will give the J80 set a try.
    Bob Schmidt

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    Default Re: String sizing and tension for an OM

    Keep in mind, if you use solid strings for the 2nd course, that will affect the way you cut the compensation on the bridge saddle. That is one fault I find with the typical entry level OMs, like Trinity College. That one comes with a bridge cut for solid-solid-wound-wound, like a regular mandolin bridge in other words. Too bad, because it is an otherwise nice (for the price) solid wood offering. Unfortunately, the intonation will never be right on those.

    A bouzouki is a different animal. Yes, the second course on an Irish bouzouki is usually solid steel. That works because of the 26 inch scale, closer to a guitar. The shorter scale of an octave mandolin requires beefier strings, and the best way to to get there is to go wound. The D’Addario J80 set is optimized for a 22.75 inch scale, so your 22 inch will make the tensions a bit lower than what they publish by a a pound or so per string. I think if you try them, you will like them!

    A couple of other things. I think it’s ok to center load the bridge. In other words, it’s good for the inner courses to be slightly higher in tension than the outside courses. This is especially true if it’s a floating bridge. Another thing, I presume your necks have an adjustable truss rod? Although, as I stated, a well made instrument can take a higher tension, I like the idea of an adjustable rod pulling the neck opposite from the string tension to fine tune any excessive relief.

    Full disclosure: I am not a luthier. But I do all my own set ups and have done a lot of custom stringing for “oddball” instruments. You would probably be surprised by how many people just throw on a set of strings without a thought about the tension. I firmly believe every instrument needs an “ideal” set to sound its best.
    Don

    2016 Weber Custom Bitterroot F
    2011 Weber Bitterroot A
    1974 Martin Style A

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  8. #6

    Default Re: String sizing and tension for an OM

    There are rules, it seems, but maybe room for experiment. For example, setting up my banjolin to mandolin tuning with mandolin strings, resulted in, to my ears, both a nasty, weak sound and the obvious effect of high string downpressure on a membrane head. Since there is no acoustic cavity to banjoish things, I tuned the same strings down one full course, and like the result, even though all nominal string tensions are now wrong. It also plays very easily. And, when I set up a mandolin to pretend to be a mandola, with a mandola C, the result was pleasing, although violation of the rules. Currently, the baglama I rescued, has supposedly appropriate strings, but they sound ok tuned every which way!

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  10. #7
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    Default Re: String sizing and tension for an OM

    I ordered a set of J80 strings to use as a starting point. Since I am making my own adjustable bridge I can get the intonation correct. I still have to dial the saddle in anyhow. I think I am on something like the sixth iteration mostly because of my being unable to make one without screwing something up.
    Bob Schmidt

  11. #8

    Default Re: String sizing and tension for an OM

    If you're interested (as I am) in knowing the downpressure on the bridge you can approximate it by multiplying the total string tension by the SIN of the break-over angle, or you can use a calculator on line https://www.liutaiomottola.com/formulae/downforce.htm In this example, 165 lbs of tension and 14 degrees break-over angle yields 39.9 lbs using the simple SIN method, and 40.2 using the fancy calculator.

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  13. #9
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    Default Re: String sizing and tension for an OM

    Thanks Brian, that is good to know.
    Bob Schmidt

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