Determining guitar balance through simple visualisation

[ixlramp]

I realised i can state the balance visualisation in a simpler way.

Determining guitar balance using visualisation
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• Find the Centre Of Mass (COM) using the method described in the first post of this thread.

• With the guitar at the playing angle you want to analyse, visualise 2 vertical lines passing through the strap buttons B1, B2.

• Consider the horizontal positioning of the COM relative to the lines.
• If the COM is halfway between the lines the guitar will be 'perfectly balanced': The weights on the ends of the strap will be equal, the strap will not want to pull forward or backward over your shoulder, the guitar will not want to rotate away from this playing angle.
  
• If the COM is closer to one line than the other, as shown in the image: The weights on the ends of the strap will be unequal, there will be more weight on the strap end corresponding to the closer line, the strap will want to pull forward or backward over your shoulder, the guitar will want to rotate away from this playing angle. However, if the imbalance is not extreme, sufficient friction between the strap and your body will prevent the guitar from rotating.
• If the COM is on one of the lines: The entire weight of the guitar will be on that end of the strap, there will be zero weight on the other end of the strap, the guitar will probably rotate.
• The ratio of the weights on the ends of the strap is equal to the ratio of the distances from COM to the lines. For example in this image: The distance from COM to the B2 line is roughly double the distance from COM to the B1 line. So the weight on the B1 end of the strap will be roughly double the weight on the B2 end of the strap.

 

[vilk]

I noticed when I've moved a couple of strap buttons from the upper horn to the back of the neck heel that the guitar gets more neckdive but also it takes less force to move it up into a high angle playing position (which also feels more comfortable). Do there might be less neck dive with the button on the upper horn, but if you want to push the neck up into a high angle it feels like lifting almost the whole weight if the guitar, as opposed to with more neck dive, yes you'll have to push it up but it's like gotta be like only a fraction of the foot/lbs that you'd have been using with the button on the horn.

Does that make sense?

 

[ixlramp]

It possibly does actually, due to the angle of a line from COM to B1: With the button on the neck heel this angle is lower, which is something that helps. It's related to how having the horn button low and close to the fretboard helps (as on a singlecut like the Abasi design). Something i'm about to address.

With the button high up on the horn, as you move to higher angles, B1 is almost above the COM, which causes problems.

 

[ixlramp]

The advantage of a singlecut or low horn button design
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For the same body blank length, having the 'top horn' button as low and close as possible to the fretboard helps balance at any playing angle above horizontal.

• The vertical line through the button is shifted away from the COM. This advantage increases at higher playing angles.

• As playing angle increases, the vertical line through the button doesn't move towards the COM as rapidly, allowing higher playing angles.

• This is closer to the 'perfectly balanced at all angles' geometry described in earlier posts (the COM being halfway along a line between the buttons).

This is the advantage of a singlecut design, but can also be done by using a claw shaped top horn like the extremely well designed Basslab STD guitar:



The advantage of using a horn is less mass is added on the neck side of the COM, helping balance.

 

[ixlramp]

'High on the butt' doesn't help
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Moving the rear strap button upwards slightly on the rear of a guitar is often recommended to help balance, but actually makes it worse.

 

[ixlramp]

Dingwall rear-mounted straplock
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Some Dingwall basses have a straplock connector mounted somewhat forward on the body back.
This is usually discussed as helping to shift the bass to the right, to help with reach on the extended scale length.
However it can be seen that a vertical line through this connector is much closer to the Centre Of Mass compared to one through the conventional strap button. So balance is also improved.

At a playing angle of 45 degrees the positioning shown is equivalent to (and is as effective as) placing a strap button at the top of the body front about halfway along the length of the body, something i suggested earlier in the thread.

 

[budda]

I have a tele with traditional button locations, but I experience slight neck dive. I dont know if my headstock is thicker than an actual Fender, but I do have a fairly thick neck. Would repositioning the top button like an SG (behind upper bout) alleviate this?

 

[ixlramp]

I'm looking at a photo of the back of a Telecaster now. I can't see anywhere the front strap button can be moved to that would improve balance. At playing angle the button cannot be moved horizontally leftwards (leftwards as seen from the player).
If you move it to body back, behind the upper bout, just above the neck joint plate, it gets shifted away from the headstock, so i suspect the advantage of having the button lower will be more than cancelled out.
As far as i can judge i don't think it will help and could even be slightly worse.

 

[budda]

Thank you for looking into it! I don't know what my locking tuners weigh, but I don't know how much that would contribute to dive.

 

[ixlramp]

Determining guitar balance using visualisation, general case, strap ends not vertical
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• Find the Centre Of Mass (COM) using the method described in the first post of this thread.

• With the guitar at the playing angle you want to analyse, visualise 2 force lines, parallel to the strap ends and passing through the strap buttons B1, B2. These represent the forces F1, F2 applied to the strap buttons by the strap ends.

• For each force line visualise a perpendicular line that passes through the COM. These lines are shown as LE1, LE2.

• Consider the lengths of LE1, LE2.

• If the lengths of LE1 and LE2 are equal the guitar will be 'perfectly balanced': The forces on the ends of the strap will be equal, the strap will not want to pull forward or backward over your shoulder, the guitar will not want to rotate away from this playing angle.

• If the lengths of LE1 and LE2 are unequal: The forces on the ends of the strap will be unequal, there will be more force on the strap end corresponding to the shortest of LE1 and LE2, the strap will want to pull forward or backward over your shoulder, the guitar will want to rotate away from this playing angle. However, if the imbalance is not extreme, sufficient friction between the strap and your body will prevent the guitar from rotating.

• The ratio of the forces on the ends of the strap is inversely equal to the ratio of the lengths LE1, LE2. For example: If LE2 was twice the length of LE1 there would be twice as much force on the B1 end of the strap than the B2 end.

 

[ixlramp]

Another in-practice example. This is my self-converted 8 string (4x2) quartertone-fretted bass, with 8 bass tuners on the headstock and a Hohner/Steinberger-copy flip-down legrest. It started as a second hand Dean Metalman V.

The Centre Of Mass (COM) is located on the fretboard at 2.5cms from the end of the fretboard.
The rear strap button i added is clearly seen on the body front halfway between the pickup and the fretboard. The front strap button is as stock and is on the back of the neck joint plate and mounted on one of the neck joint screws, i added an arrow to point to it.

So the COM is near-halfway between the strap buttons, the rear strap button should be even closer to the neck joint but i was concerned about a strap end touching the strings.

It balances very well and is very comfortable, despite these strap button positions looking crazy. Not having the strap pulling forward on your shoulder improves comfort.
The right end of a strap wraps around the right side of your body and so pulls the bass to the right, putting it in a very ergonomic left-right position with both 1st fret and bridge comfortably reachable.

 

[ixlramp]

When a guitar is supported on one leg, it will balance when the Centre Of Mass (COM) is vertically above the point in the leg cutout where the body edge is horizontal.

You can use this fact to roughly judge where the COM of a guitar is from a photo of someone playing one.

 

[cynicown]

Cheers for such useful info! Going off of what you've stated above, where do you think the ideal strap positions would be on the Ibanez xiphos? I've tried them in a number of positions and never really found the magic formula.

 

[Konfyouzd]

As usual, the answer is "just get a used Ibanez prestige".

 

[ixlramp]

cynicown please post a front-on photo with the centre of mass marked (you can find it using the method in the first post). Or if you can precisely describe where the COM is that's ok too.
What playing angle (or what range of playing angles) do you use? 24 or 27 frets? 6 or 7 strings?
Xiphos will be tricky as it has a short top horn.

 

[ixlramp]

The technical stuff
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This is so anyone good at mechanics can check this, i hope it is checked.

My results come from a torque analysis of a guitar on a strap and therefore affected by 3 forces:
The 2 upward forces 'F1', 'F2' of the strap ends, applied to the strap buttons 'B1', 'B2'.
The downward weight force 'mg' that is applied to the centre of mass 'COM' ('mg' is mass * acceleration of gravity).



'Torque' is a twisting force at a pivot, or axis.
In this torque analysis i choose an axis on the guitar and calculate the 3 torques created at that axis by the 3 forces.
The trick is to choose the axis to be 'COM'. The torque of force 'mg' is therefore zero as it passes through this axis, so i now only have to consider 2 forces and 2 torques. It's also intuitive to consider the guitar rotating around it's centre of mass, objects tend to do this.
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Now i consider the general case of how to calculate the torque at axis 'COM' created by a force 'F' applied to point 'B' which is distance 'L' from the chosen axis 'COM'.



Torque is calculated by multiplying the length 'L' by the perpendicular force 'FP' applied to 'B'.
Torque = FP * L
'FP' is the component of force 'F' perpendicular to 'L' (Force 'F' can be considered equivalent to the 2 components 'FP' and 'FL', where 'FL' is parallel to 'L'.)
FP = F * cos(A)
Where 'A' is an angle
Torque = F * cos(A) * L

I have marked 2 angles on the diagram, both called 'A', they are equal angles.
'LE' is a line perpendicular to force 'F'.
Notice that
LE = L * cos(A)
So the torque equation above can be written
Torque = F * LE
This proves that torque can be calculated by multiplying force 'F' by the distance 'LE' measured along a line perpendicular to 'F', as if the force 'F' is being applied to point 'BE' instead of 'B'.



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Since the guitar is not rotationally accelerating around axis 'COM' i know that the torques created by 'F1' and 'F2' are equal and opposite, cancelling each other out.



So
F1 * LE1 = F2 * LE2
Re-arrange to
F1 / F2 = LE2 / LE1
"The ratio of F1 and F2 is equal to the ratio of LE2 and LE1."

When the guitar is perfectly balanced, the forces on the ends of the strap are equal, so
F1 = F2
So
F1 / F2 = 1
So
LE2 / LE1 = 1
So
LE2 = LE1

 

[KVNTZ]

View attachment 67371

Another in-practice example. This is my self-converted 8 string (4x2) quartertone-fretted bass, with 8 bass tuners on the headstock and a Hohner/Steinberger-copy flip-down legrest. It started as a second hand Dean Metalman V.

The Centre Of Mass (COM) is located on the fretboard at 2.5cms from the end of the fretboard.
The rear strap button i added is clearly seen on the body front halfway between the pickup and the fretboard. The front strap button is as stock and is on the back of the neck joint plate and mounted on one of the neck joint screws, i added an arrow to point to it.

So the COM is near-halfway between the strap buttons, the rear strap button should be even closer to the neck joint but i was concerned about a strap end touching the strings.

It balances very well and is very comfortable, despite these strap button positions looking crazy. Not having the strap pulling forward on your shoulder improves comfort.
The right end of a strap wraps around the right side of your body and so pulls the bass to the right, putting it in a very ergonomic left-right position with both 1st fret and bridge comfortably reachable.

I've got absolutely no clue how this position works, the distance between the strap points is small small your strap must wrap around your stomach. What does it look like on your body when you play it?

 

[KVNTZ]

Additionally how do you determine the end point of F1? Is that basically the length of the strap from button to the tip of the shoulder?

 

[ixlramp]

Heh, yes that is quite an extreme conversion. The right side strap end wraps around your body a little, and depending on how high the instrument is it can be uncomfortable having the strap digging into your side (this is a possible problem with some of the 'solutions' i describe). However, the balance itself is pleasant. Also, this pulls the bass guitar to the right quite a lot, which i find comfortable.

The length of the line labelled with F1 is irrelevant and unused in the maths, the F1 value in the maths is a force value, the amount of force pulling upwards on button B1. In fact you never need to know what F1 or F2 are, because the result of all this is that, for perfect balance, the distances LE1 and LE2 must be equal.

 

[ixlramp]

I might have misunderstood, perhaps you were not asking about the length of that line but how to choose its angle?
The correct angle of the F1 or F2 force line is simply the angle of the strap end close to the button.
A strap will change its angle as it passes over the players body but that is irrelevant.