Tension on mandolin tops from strings

[Pete Summers]

According the the package on my D'Addario J73 strings I just purchased, there is a combined tension of 157.4 pounds with all eight strings tuned to A440. Wow. Is that right?

That seems like a lot of tension to put on the top of my lightly constructed Kentucky Army/Navy mandolin, or any other mandolin for that matter. And these are light strings. That's like having my grown son stand on top of the mandolin. No wonder necks bow and tops sink.

I'm amazed. I thought the tension would be around 40 or 50 pounds on a mandolin. Color me incredulous.

[Marty Henrickson]

Quite so. In fact, it's amazing how luthiers manage to build an instrument that vibrates freely enough to create sound, yet doesn't implode under all this constant tension. I believe an acoustic guitar holds up to 200+ pounds of tension.

[MONami]

If you actually mean you are incredulous, do an experiment.
Using your fingers try to pull up on the bass side strings at the bridge,
to take enough tension off to to rotate the adjuster dial freely.
Can't do it huh? That is some tension. Maybe not 180, but alot of #

[Canoedad]

Tension and downward pressure on the top are not the same. It will take one of our engineers to say how much downward pressure there is from that tension. All I can say is the higher the bridge, the more downward top pressure.

[Bill Snyder]

According to Graham McDonald's string tension calculator a steel string guitar with medium strings has about 165 lbs of tension on the top. According to the same calculator a set of J73's on a mandolin with a 13 7/8" scale length will have about 160 lbs of tension.
The string tension calculator can be found HERE.

[Jim Rowland]

The bridge should divvy up that tension between the top and the tailpiece shouldn't it? I really don't know and am a dunce in physics.

Jim

[Tom Wright]

The tension number listed is only the combined tension along the strings.

One does feel intuitively that downward pressure would depend on bridge height, in that if there were no angle difference across the bridge there would be zero pressure. As to how much is optimal that is another question. In the case of a glued-on bridge there is no downward pressure at all, but some upward pull, which will be sensitive to the height of the bridge saddle above the top.

[sunburst]

The downward pressure on a carved top mandolin is usually around 50 to 60 pounds, IIRC. String tension and the angle that the strings break over the bridge determine the downward pressure, not bridge height per se. For example, a higher top arch can have a lower bridge than a lower arch, and the two can have the same break-over angle.
I used to say, "imagine a first grader standing on top of the bridge" to give people a mental picture of the force that in involved, until someone said "I can only imagine a first grader jumping up and down on the bridge". I'm still trying to think of another analogy...

[Marty Henrickson]

I refuse to allow any first-graders on my bridge, under string tension or not.