Determining guitar balance through simple visualisation

Discussion in 'Luthiery, Modifications & Customizations' started by ixlramp, Dec 8, 2018.

  1. ixlramp

    ixlramp SS.org Regular

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    I worked through the mechanics of the forces and torques and have derived a simple way to consider and perfect guitar balance through visualisation.

    This is very useful to know as a large majority of guitars have poor balance, even at fairly horizontal playing angles, and balance that becomes rapidly worse at higher playing angles. On an existing guitar balance can often be perfected by moving the strap buttons.

    The intention here is to equalise the forces pulling on each end of the strap while the guitar is at a particular playing angle, so that there is zero tendency for the instrument to rotate. This stops the strap pulling forward on your shoulder, which is unhealthy, with only friction stopping the guitar neckdiving.

    When designing a guitar this knowledge is very helpful to create a design with good balance, it's also possible to create a design that balances perfectly over a wide range of playing angles.

    First, find the 'centre of mass' (COM)
    -----------------------------------------------
    This is often called the 'centre of gravity'.
    In mechanics it is very often possible to simplify analysis by considering all the mass of an object to be concentrated at one point, the COM.

    The method used is balancing the guitar on and above one hand by pinching the lower body edge between thumb and first finger, in a way that allows the guitar to pivot at that point (pivot point).
    This hand is probably best resting on your knee to avoid fatigue.
    The other hand shifts and stabilises the guitar until it balances, at which point it is barely touching the guitar.

    1. Balance the guitar on your hand with the guitar perfectly vertical, and shift the pivot point left and right until the guitar balances vertically without falling left or right.
    Now we know the COM is somewere directly above the pivot point, you could mark the pivot point or just remember where on the instrument the vertical line above the pivot point is. It will often be near the centreline of the guitar:

    COMvert.png
    2. Now do the same with the guitar perfectly horizontal.

    3. Where the 2 lines cross is the position of the COM:

    COMhori.png
    (Continued below)
     
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  2. ixlramp

    ixlramp SS.org Regular

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    Balance visualisation
    --------------------------
    1. With the guitar at the playing angle you want to analyse, visualise 2 vertical lines passing through the strap button points B1, B2.
    2. Visualise a horizontal line passing through the COM point and visualise the points E1, E2, where it crosses the vertical lines.

    RGbalance_points.png
    3. The magnitudes of the forces pulling on the strap ends will have a ratio equal to the ratio of the distances E1 - COM and E2 - COM.
    The shorter the E - COM distance is, the larger the force is on that end of the strap.
    If the distances E1 - COM and E2 - COM are equal the forces will be equal and the guitar perfectly balanced.

    Above you can see the distance E2 - COM is roughly twice the distance E1 - COM, so the force on the horn end of the strap will be roughly twice that of the force on the rear end of the strap.
    (Note i have probably incorrectly guessed the COM point for this Ibanez RG, the diagram is meant to be general not specific to this guitar.)
     
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  3. crackout

    crackout The King In Yellow

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    I would not call this 'perfectly balanced' in the understanding of a nicely hanging guitar.
    If both forces are equal, you will have no 'restoring force' into the desired position, the guitar will always stay the way you put it. While technically speaking this is well-balanced, at least to me in addition to a nice hanging position a guitar should also have a tendency to move there.
     
  4. ixlramp

    ixlramp SS.org Regular

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    If you require a tendency to return to the desired playing angle, the forces on each end of the strap must be equal when at that angle, if they are not that won't be the equilibrium angle, a different angle will be.
    However yes whether there is a restoring force or not is determined by stuff i haven't described yet, where the buttons are located.

    I actually consider the perfect system is one that has zero restoring tendency, that is, perfect balance over a wide range of angles, otherwise you are forced to use a single playing angle, and playing angle is determined by personal taste and what techniques you are using. Fine for personal modifications or custom work, but otherwise a manufacturer should not really dictate what playing angle the player can use (but most designs do dictate this).

    Almost all conventional guitar and bass designs have perfect balance only when the neck is pointing downwards to some degree. That is, friction of strap on shoulder is the only thing that keeps a guitar at the desired playing angle.

    I continue with further posts.
     
  5. ixlramp

    ixlramp SS.org Regular

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    The solution
    ----------------
    The strap buttons should be placed somewhere on vertical lines that are equidistant either side of the COM.

    But with one condition: If a line is imagined between the strap buttons, the COM should be on or below this line, otherwise the COM is above the supporting axis and the guitar will be unstable and tend to flop forwards or backwards (that is, away or towards the player).

    So for the guitar in the images, we need to either move one or both the strap buttons to the right, and/or move the COM towards the left.
    We can't move the COM without adding weight, which is a bad idea for comfort and health.
    Moving the horn button to the right is only possible with an ugly and costly horn extension.
    So the remaining solution is moving the rear button to the right.

    A solution i have used on several guitars is to place the rear button on the front of the body, near the top and roughly halfway along the body:
    RGbalance_solved.png
    Placing the button on the body front tends to tilt the guitar towards the player slightly so that the fingerboard is more visible.

    Obviously this solution is possibly not suitable for many guitar (as in, not bass guitar) players as it will shift the guitar to the right a little. However it is very helpful for a bass guitar because basses are positioned too far to the left when strapped on, when the bridge could be shifted to the right comfortably.

    The result is a horizontal position closer to the position created when placing a guitar on your right thigh, which for a bass guitar is a far more ergonomic position.
     
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  6. ixlramp

    ixlramp SS.org Regular

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    The 'solution' shown in the previous post will have the restoring behavour discussed earlier, because the COM is significantly below the line between the strap buttons. If the guitar angle changes the COM rapidly becomes closer to one or the other vertical lines in a way that tends to restore to the perfectly balanced angle.

    The common problem
    ----------------------------
    The diagram in the post 2 is for a guitar angle of 30 degrees and the guitar is already significantly unbalanced. The diagram below is for a guitar angle of 45 degrees which is quite commonly used:
    fortyfive_lines.png
    This shows the very common balance problem most guitars have. As the playing angle increases the guitar rapidly becomes extremely unbalanced as the COM moves to be almost directly below the horn strap button.
    Here there is roughly 5 times as much weight on the horn end of the strap as on the other end, probably overcoming strap friction and making this angle unmaintainable.

    Such a high playing angle is good for ergonomics and is popular with more technical players and metal guitarists. Bass guitars especially benefit from a high playing angle, angles even steeper than 45 degrees work very well for the arms and wrists.

    When the electric guitar and bass were developed in the 50s/60s it seems they were designed to be played near-horizontally. A button was placed on each end and it just about worked with the guitar near-horizontal. The guitar was unbalanced but strap friction was enough to overcome that.

    Considering how revolutionary the electric guitar and bass were at the time i can forgive not much thought being put into the mechanics of balance.
    However, since the Strat and P-bass were designed, nothing has changed in the mainstream in 60 years in terms of strap button positions, body shape, ergonomics and instrument balance, apart from some brief but temporary progression in the 80s (Steinberger and headless).
     
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  7. crackout

    crackout The King In Yellow

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    From my observations the COM always lies 'underneath' the anchor point of the strap (on your shoulder).
    Moving the strap pins moves the guitar relative to the anchor point and the guitar will rotate in a way so the above statement is fulfilled.
     
  8. ixlramp

    ixlramp SS.org Regular

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    The only way the COM can be vertically below your shoulder is not connecting the other end of the strap, because the other end exerts a force on the guitar.
    If you imagine hanging the guitar from a strap only connected to the horn button, the guitar will rotate such that the COM will be vertically below the horn button.

    However you're somewhat correct in a way, but it's probably because almost all guitars are neck-heavy, so the COM is fairly near to being below the horn button, you can see this is the case for 30 and 45 degrees.
     
  9. crackout

    crackout The King In Yellow

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    I'm not saying the COM will lie underneath the horn button but the anchor point where the strap sits on your shoulder (the tip of the triangle formed by both strap segments and the imaginary line so to say). It doesn't matter where I put the anchor point on the strap (i.e. how I divide the strap), the COM always lies underneath the anchor. To achieve this, the guitar will rotate. You can easily verify this by marking the COM and hanging the guitar over your hand. The COM will lie directly underneath your hand (low friction strap recommended).

    With neck-heavy guitars, the COM lies further to the headstock while your anchor point on your shoulder remains more or less in the middle of the guitar body.

    Bild1.png

    SGs are a prime example for neck-heavy guitars. The thin body combined with the bad button placement and the fact that these necks do not protrude into the body at all moves the center of mass almost on the heel. The resulting torque is large enough to overcome the static friction of the strap (because SGs are very light guitars) resulting in dive.

    Bild2..png

    By diving down the COM will reach its desired position underneath the anchor point.

    With a "proper" design and good weight balance between body and neck, you can push the COM into the body whilst moving the upper button further out and thus move the guitar body as well. This helps moving the COM underneath your anchor.

    Bild3..png

    I don't see why the fundamental principle should be different depending on the number of the fixture points (1 or 2). There will always be a net torque as long as the COM is not directly underneath the anchor.
     
  10. crackout

    crackout The King In Yellow

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    Of course, above behaviour only applies if the anchor point lies between both button points.
    If it lies outside this range (e.g. a SG with a super light body and a COM even further oriented to the headstock), the headstock will dive all the way down.
     
  11. AeroSigma

    AeroSigma SS.org Regular

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    One of the problems with moving the body button up is that the loop between the strap mounts is thin, and uncomfortable around the shoulders. While this might not be an actual issue, I would expect this is the reason that the current way of doing it became standard.

    Consider that many acoustic guitar straps anchor on a button on the end of the body, but then wrap around the neck above the nut, which avoids the neck dive issue. You could solve this issue by using that type of strap: https://i.ytimg.com/vi/BqLnrT_fu2A/maxresdefault.jpg

    Another thing to consider is adding an extension to the upper horn to move that button further from the CoG. Perhaps similar to the way Anygig does it: https://i.ebayimg.com/images/g/7JQAAOSwrh5bcTXR/s-l640.jpg
     
  12. ixlramp

    ixlramp SS.org Regular

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    crackout, i see what you mean now thanks.
    So far i have assumed the strap ends are vertically above the strap buttons, but i need to address a general case where the strap ends are at any angle.
    In a way the strap doesn't form a triangle because one end of the strap comes around the right side of your body so approaches the rear button from roughly above. When a player wears a guitar the horn end of the strap tends to be near-vertical up to the shoulder.
     
    Last edited: Dec 18, 2018
  13. ixlramp

    ixlramp SS.org Regular

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    Balancing the Hohner B2(A)V
    -------------------------------------
    My first 2 basses were a Hohner B2V and a Hohner B2AV. These are shifted well to the left when strapped on and are fairly unbalanced despite being headless. I was interested in 2-hand tapping and needed a higher playing angle.
    I intuitively decided having the COM horizontally equidistant between the buttons would help. On both i added a new button on the body front halfway between the pickups:

    hohnerb2av_balance.png
    'B' shows the buttons i used, 'BO' is the original rear button.
    This works out very well because at a playing angle of roughly 22.5 degrees: It is perfectly balanced, but also, the buttons are level and the COM only a small distance below.
    This maximises the range of playing angles usable, it can go from horizontal to 45 degrees and never be more than slightly unbalanced.

    The moved rear button also pulls the bass to the right which was much needed.
    It was very comfortable, much more than before.

    Conventional guitars and basses start out already neck-heavy when horizontal and this only gets worse at higher angles, so the range of usable playing angles is much reduced.
     
  14. ixlramp

    ixlramp SS.org Regular

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    Perfect balance at multiple playing angles
    -----------------------------------------------------
    • If the COM is halfway along a line drawn between the strap buttons it will always be horizontally equidistant from vertical lines drawn through the buttons. Resulting in perfect balance at multiple playing angles.
    • Ideally the line between the strap buttons should be as close as possible to being horizontal when the guitar is at an angle halfway between the most extreme playing angles used. This maximises the horizontal distance between the strap buttons over the playing angles used.
    Below is a suggestion for a headless guitar with perfect balance at multiple playing angles. I have guessed the location of the COM.
    (This body shape i consider one of the most ergonomic designs, the guitar is by Rick Toone).

    viceroy_balance2.png

    This design helps because:
    The COM is horizontally closer to the middle of the guitar.
    The COM is above the centreline of the strings.
    The singlecut design allows a strap button low and close to the neck near the 12th fret.

    It's not ideal as the line between the strap buttons is near-horizontal, and slightly back-angled, when the guitar is horizontal, which isn't the middle playing angle.
     
    Last edited: Dec 23, 2018
  15. gunch

    gunch chungus

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    so is the TDLR that RGs are the most comfortable shapes outside of purposefully ergo designs like kleins and breadwinners?
     
  16. LiveOVErdrive

    LiveOVErdrive CNC hack

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    As usual, the answer is "just get a used Ibanez prestige". :)
     
  17. ixlramp

    ixlramp SS.org Regular

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    No, the opposite, maybe you DR?

    I criticise the RG / superstrat / strat design as being inherently poorly balanced, especially at higher angles.
    Having no development for 60 years, stagnated by '1960's rock band fashion' (which perhaps needs to finally go out of fashion).
    The basic shape is an acoustic guitar from several hundred years ago plus 2 cutouts added by Fender. Fender did little to advance design, but as stated i can forgive that as the electric guitar was a revolution at the time.
    This is all without considering ergonomics while sitting which are far worse and cause unhealthy posture, back twisting.
     
  18. ixlramp

    ixlramp SS.org Regular

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    Multi-angle perfect balance for bass guitar and touch guitar
    ---------------------------------------------------------------------------
    These instruments are playable over a wider range of angles than guitar, between 0 degrees (horizontal) and around 80 degrees (near-vertical).
    The bridges of these instruments are more right-shifted, relative to the player, than guitar.
    Together these allow a different approach to strap button placement.

    Warr Guitars
    ----------------
    The first time i encountered this innovative strap button placement was seeing the 'Warr Guitar' touch guitars.
    These instruments are designed to be played either near-vertical like a Chapman Stick, when using 2-handed tapping, but also designed to be played at lower angles when using conventional guitar and bass techniques.

    12+nt+fig+maple_800_IND.png

    The horn button has been moved to the back of the lower horn. The rear button has been moved to the upper body 'waist'.
    The buttons are level with each other at a typical playing angle (60 degrees).
    The COM is likely to be roughly midway between the 2 buttons.
    This geometry is now also used by 'Touch Guitars' http://www.touchguitars.com/models-specs/.

    From the mechanics of earlier posts in this thread, it can be seen why this works so well, as it is close to the geometry that creates perfect balance at multiple playing angles.
    The geometry helps to shift the instrument to the right, for horizontal position closer to that when resting the instrument on your leg. Ideal for a touch guitar but also good for bass guitar, as most bass guitars are shifted too far to the left when on a strap: The nut is uncomfortably far away but the bridge can comfortably move to the right.

    Below is Trey Gunn (played in King Crimson at one point) and his signature Warr Guitar perfectly balanced at a high angle.

    1c526b642090e245013c092e217e8ce5.jpg

    Applying the Warr Guitar geometry to bass guitar
    --------------------------------------------------------------
    Here i will use a Hohner The Jack 4 string as the example, which helps this geometry due to being headless and therefore having a COM that is a little more central to the body. I also own one so i know where the COM is.
    However, this example is meant to represent any bass guitar, and this geometry can be used for headed bass guitars.

    Bass guitars are playable from 0 to 80 degrees, so i take 40 degrees as the mid angle and rotate the image of the bass to this angle. (Bass guitars may not often be played at 80 degrees but that's because their poor design makes that almost impossible, bass guitar is actually very comfortable and healthy played at very high angles).
    I then try to keep the line between the strap buttons as horizontal as possible, and make sure the COM is halfway between the strap buttons.

    jack_40_balanced_IND.png

    One button would be placed on the back of the lower horn (alternatively it could be placed on the side of the lower horn at the same position, to allow placing the instrument in a hardcase), the other on the body front.

    Note that placing buttons on the front or back of the body results in a safe and secure strap connection at any playing angle, unlike conventional horn button placement where the strap wants to pull off the button at high angles. (This is something i like about the Ibanez BTB design, see my avatar, the horn button is angled downwards).
     
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  19. LiveOVErdrive

    LiveOVErdrive CNC hack

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    Cool stuff. I'd be concerned about the strap getting in the way of my hand on the neck though, when it is on the lower horn like that.
     
  20. ixlramp

    ixlramp SS.org Regular

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    Yes that is something to be careful of, the Warr geometry tries to keep the button near the base of the lower horn, and i have tried to do this on the The Jack example too.

    I discovered this issue when i modified my Crafter Cruiser RG600 (i added quartertone frets), an Explorer type shape with no top horn. I placed the button on the tip of the lower horn, and noticed that at high playing angles the strap would slightly get in the way of my fretting arm.
    Balance and comfort is excellent though at any angle. It's interesting how much more comfortable it is when the strap is not trying to pull forward over your shoulder, which happens on most guitars.
    Here you can see the button locations:

    DSC02034cropThird.jpg

    The Warr geometry is useful for balancing guitars which have no top horn and therefore even worse balance issues.
     

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