Round vs. hex core string stiffness

[David Jayne]

Everyone knows that round-core strings have less tension than hex-core strings. Anyone know why? I just put on a set of Lo-Riders, where I'd previously used Sunbeams and although I was aware that Lo-Riders would be tighter than Sunbeams, I was unprepared for just HOW MUCH tighter they actually are. I had to tighten the truss rod quite a bit, and do a general setup to get it playable.
So, why? Why the difference, when the gauges are the same? I truly don't understand how there can be such a large difference.

 

[FunkMetalBass]

Tension is determined by the vibrating frequency, scale length, and string mass per unit length. A hex core has more mass than the round core:

For a circular core of radius R, the area of the circle is pi*R^2. For the circumscribed hexagon, the area is 6*R^2/(sqrt3). The hex core will have about 10.2% more mass per unit length than the round core.

 

[David Jayne]

OK, I get that, but why not just use a larger, round wire? What happens to the wrap wire as it's brought around the hex core? Is it simply displaced by the hex corners? Do we know for sure that the hex wire is, in fact, larger point-to point, that the round wire used in Sunbeams?

 

[FunkMetalBass]

OK, I get that, but why not just use a larger, round wire?

What's the intended purpose of increasing the larger core? Tension? If that's the case, you have to use thinner wrap wire, and from a previous set of calculations that I did in another thread, increasing the core size and decreasing the wrap size doesn't really give you an appreciable gain in overall mass (I think it was less than a 4% increase). Also, string makers have tonal reasons for choosing the gauges they do. Two strings of the same gauge but with different core and wrap sizes will sound and feel significantly different.

If you want to use a larger core and keep the same wrap wire to increase tension, then you have to increase the gauge, and since many bassists are terrified of sets that aren't .100 - .045, you've just lost a lot of potential market

What happens to the wrap wire as it's brought around the hex core? Is it simply displaced by the hex corners?

My understanding is that the wrap wire is actually bent around the hex corners, but with the wrap compression and addition of second and third wraps, it's unnoticeable. This would also mean that wraps wont slip off the core as easily, so doing the right-angle bend before cutting (like you have to do on your round core DRs) is not really necessary.

Do we know for sure that the hex wire is, in fact, larger point-to point, that the round wire used in Sunbeams?

If there is significantly more tension with the same gauges, I'm 99% positive that's the case. And, if ordering music wire is the same as metal bars, sizes are measured side-to-side, not point-to-point. Invalid Link Removed

 

[NKUSigEp]

Tension is determined by the vibrating frequency, scale length, and string mass per unit length. A hex core has more mass than the round core:

For a circular core of radius R, the area of the circle is pi*R^2. For the circumscribed hexagon, the area is 6*R^2/(sqrt3). The hex core will have about 10.2% more mass per unit length than the round core.

Couldn't this just as easily be perceived as a hexagon inside of the circle, therefore giving the rounds more mass?

 

[Dave W]

Couldn't this just as easily be perceived as a hexagon inside of the circle, therefore giving the rounds more mass?

Exactly what I was thinking.

Using the picture, I would think the round core string would be say, a standard .105...and the hex would be more like a .107.

Or is that just how string manufactures do it? For the same size string the round would fit inside of the hex...thus making it slightly larger, but still marketed as the same size?

 

[FunkMetalBass]

For the same size string the round would fit inside of the hex...thus making it slightly larger, but still marketed as the same size?

That I can't really answer because I don't work in the string industry and have never wound the strings myself. Everything I do know comes from my physics knowledge and many conversations with Skip, the Circle K owner (who I think has stopped posting here).

I can tell you, though, that I've taken a caliper to strings and found that they can vary by as much as +/-.0025" from what the manufacturers claim they the gauges are.

 

[FunkMetalBass]

Couldn't this just as easily be perceived as a hexagon inside of the circle, therefore giving the rounds more mass?

That was my original thought too, but Skip at Circle K stated that hex-core strings consistently had more mass than round-cores. Also, Invalid Link Removed talks about the wrap wire "biting" the hex core vertices.

The only logical explanation that I see is that the hexagon circumscribes the circle, as in the image I posted.

Seriously, I'd love for a knowledgeable string maker to objectively chime in on the subject.

 

[mmbongo]

Couldn't this just as easily be perceived as a hexagon inside of the circle, therefore giving the rounds more mass?

Just what I was thinking, as every string manufacturer I know of states that round core has more mass than hex core. I don't know. I just know I love the feel of round core strings like DR Sunbeams. I'm going to try Dean Markley's as well, now that Jason at Bass Strings Online sells them, they're a good bit cheaper than Sunbeams.

 

[Creese]

OK, this is getting back in my brain where the cobwebs are and sorry to geek out, but:

1) Wouldn't perceived tension (bending) of the string at your fingers have more to do with the section modulus of a hex vs. cylinder core (given same cross sectional area ie: mass), and
2) As previously stated, tension relative to the truss rod (strain) more so the collective cross-sectional mass?

...I'm not sayin', I'm asking...

 

[mmbongo]

OK, this is getting back in my brain where the cobwebs are and sorry to geek out, but:

1) Wouldn't perceived tension (bending) of the string at your fingers have more to do with the section modulus

Bass brand shouldn't matter. Modulus, Fender, Warwick, Music Man...

 

[FunkMetalBass]

Just what I was thinking, as every string manufacturer I know of states that round core has more mass than hex core.

Can you show me sources for these? I'd like to try to get in touch with some of the manufacturers and ask them some of the more technical questions that this thread has raised.

OK, this is getting back in my brain where the cobwebs are and sorry to geek out, but:

1) Wouldn't perceived tension (bending) of the string at your fingers have more to do with the section modulus of a hex vs. cylinder core (given same cross sectional area ie: mass), and
2) As previously stated, tension relative to the truss rod (strain) more so the collective cross-sectional mass?

...I'm not sayin', I'm asking...

Oh boy, materials science, something I don't remember too much about (quantum theory is more of my area). But I'll give it a shot.

1) Yes, the section modulus and cross-sectional area are used to determine the flexibility (a term I prefer to "perceived tension", but to each his own) of a material. I'm not entirely sure how one would derive the modulus for a particular shape, but if we compare the section modulus of a square and a circle of equivalent cross-sectional area, the square will have a higher section modulus (ratio: S_square/S_circle = r*sqrt(pi)/6) and thus be more resistant to bending.

2) Tension of a string is directed axially and does not rely on the sectional modulus, only the mass per unit length, vibrational length, and vibrational frequency.

The two measurements are, in fact, independent, but this comes with the caveat that there is a necessary correlation between flexibility and tension in the real world. Because tension is mass-dependent, increasing the mass requires a larger cross-sectional area and will certainly yield a higher sectional modulus, and thus making the string more inflexible.

Bass brand shouldn't matter. Modulus, Fender, Warwick, Music Man...

LOL.

 

[mmbongo]

Can you show me sources for these? I'd like to try to get in touch with some of the manufacturers and ask them some of the more technical questions that this thread has raised.

Dean Markley
[Invalid or Expired Link Removed]

DR explains it right on the back of the Sunbeams package.
DR Strings | THE HANDMADE STRING IN GOOD HANDS. YOURS.

Second post down, David from SGD Lutherie:
Lots of good info as you go down
Hex/Round Core Strings & Relationship to Tension/Stiffness

 

[David Jayne]

In the article that mmbongo linked, DR states the following, regarding round core strings:

"More evenly distributed pressure in the windings typically results in:

1 - Lower overall tension......"

OK, but WHY? How can the distribution of winding pressure affect tension???? I believe them if they say so, but I don't understand it, at all.

 

[FunkMetalBass]

OK, but WHY? How can the distribution of winding pressure affect tension???? I believe them if they say so, but I don't understand it, at all.

It doesn't. Tension is a physical measurement that relies on three things, and three things only: mass, pitch (the vibrational frequency), and scale length (vibrational length).

The statement regarding low tension is either unrelated, or it is improper use of the word "tension" to describe string flexibility.

 

[FunkMetalBass]

Dean Markley
[Invalid or Expired Link Removed]

DR explains it right on the back of the Sunbeams package.
DR Strings | THE HANDMADE STRING IN GOOD HANDS. YOURS.

Second post down, David from SGD Lutherie:
Lots of good info as you go down
Hex/Round Core Strings & Relationship to Tension/Stiffness

Cool. I have some reading to do. Thank you.

 

[KJung]

It doesn't. Tension is a physical measurement that relies on three things, and three things only: mass, pitch (the vibrational frequency), and scale length (vibrational length).

The statement regarding low tension is either unrelated, or it is improper use of the word "tension" to describe string flexibility.

Yeah, I think we use 'tension' very loosely on this site to describe the 'feel' of the string (i.e., the more 'rubbery feel' of the DR strings with round cores).

Also, to the OP, I assume you realize that the stainless steel versions of your Sunbeams are Hi Beams. So, if you want a stainless steel strings that has that smooth, somewhat loose feel of the Sunbeams, it would be the Hi Beams for you. Wonderful strings!

 

[FunkMetalBass]

Dean Markley
[Invalid or Expired Link Removed]

DR explains it right on the back of the Sunbeams package.
DR Strings | THE HANDMADE STRING IN GOOD HANDS. YOURS.

Second post down, David from SGD Lutherie:
Lots of good info as you go down
Hex/Round Core Strings & Relationship to Tension/Stiffness

Oy, so much weird information there, and the only thing I got out of it was that Dean Markeley uses round cores that are larger than the hex cores. David said the same thing, but I have no idea where his information comes from.

And none of it solves the "more tension" problem.

 

[David Jayne]

It doesn't. Tension is a physical measurement that relies on three things, and three things only: mass, pitch (the vibrational frequency), and scale length (vibrational length).

I'd have thought so too, it seems perfectly obvious. But DR says otherwise.
I had a theory, but it didn't pan out: I took the E strings off of my basses and weighed them on a fairly accurate food portion scale, after insuring they were the same length. My caliper says they are both .106" diameter. Sunbeam comes in at 1.3 Oz, and a Lo-Rider appears to be slightly lighter- the scale display bounced between 1.2 and 1.3 Oz., which is the opposite of what I expected to find. Hmmm.....

 

[David Jayne]

Yeah, I think we use 'tension' very loosely on this site to describe the 'feel' of the string (i.e., the more 'rubbery feel' of the DR strings with round cores).

I hear you, Ken, but is that really it? Because the Lo-Riders really seem to have more actual tension.
I can't find at-pitch tensions anywhere on the DR site. That would be telling.