Acoustic Guitar Setups

Acoustic Guitar Setups

Setting up a steel string acoustic guitar to be all that it can be requires knowledge of the construction and maintenance process(es) of the instrument, quality tools and the skills to use and maintain them, experience to answer questions, offer suggestions, make recommendations as well as informed decisions, and respect for and knowledge of the player into whose hands the guitar will be placed.

And here you were thinking that anyone with a string winder should be able to do a good job!

Playability

The purpose of an acoustic guitar setup is to improve the playability of the instrument - as perceived by the person who will be playing it.

Several things must come together for an acoustic steel string guitar to be considered eminently playable. Factors such as body size and shape, overall weight, neck width and depth (or "thickness"), as well as features like arm bevels, cutaways and sound ports all contribute to my perception of a comfortable guitar. However, these design elements and features have already been established by the time the guitar maker, luthier or guitar technician takes on the task of performing a proper setup.

Ensuring correct neck geometry is absolutely essential in order to deliver a well-set up guitar. The perfectly flat plane of the strings, secured at one end at the headstock and (typically) secured at the other end onto or into the bridge, must be close enough to the fretboard to be pleasant to play while not being so close that strings make constant contact with the frets, causing a "buzzing" sound. This is primarily determined by an accurately set neck, though there are additional elements that are adjustable, either in part or fully. How well all of these elements are addressed will ultimately determine the playability of any given guitar:

• Fretboard condition
• Fretboard flatness
• Fret condition
• Nut (material, fit, string spacing, slot depth)
• Truss rod functionality and setting (if so equipped)
• Relief
• Fall-away (any or none)
• Bridge condition (including attachment issues)
• Bridge height
• Saddle slot positioning (compensation)/depth/flatness, etc)
• Saddle (material, height, intonation)
• Bridge pin holes and pins (if so equipped)
• String ramping (or not)
... and more!


Before we jump in and start making changes, however, we need to perform an assessment of the condition of the instrument. Much like an automobile, a guitar is the sum of many parts. When excessive wear and/or mis-alignment(s) are present, these must be addressed if we are hoping for high-performance results.

We will check the following:

1. Neck Bow and Twist
2. Neck Geometry
3. Action (String height at the 12th fret)
4. Frets and Fretboard Condition
5. Nut Slots and Saddle Height
6. Torque and Overall String Height
7. Break Angle
8. Bridge Shaving/Bridge Height
9. Bridge Lift
10. Bellying and Brace Assessment

1. Neck Bow and Twist

A wooden guitar neck is essentially a straight plane. I say 'essentially', as a given guitar neck may have just the slightest amount of forward bow in it, depending upon a player's preference for relief. Relief refers to a deliberate introduction or allowance of concavity along the surface of the fretboard/fret plane in an attempt to mitigate string buzz, the result of the strings contacting the metal frets as they oscillate. Additionally, the fretboard extension, that part of the fretboard that extends beyond the point where the neck joins the body, may include fall-away. This is a slight, but deliberate sloping of the fretboard away from the path of the oscillating strings.

On a guitar having a perfectly flat neck, depending on the overall stiffness of the neck and the gauge of the strings, some forward bow will likely occur due to the pull of the strings. If additional bow is desired, more relief can be introduced by planing, carving or sanding material away from the fretboard or, if your guitar is so equipped, by making an adjustment to the truss rod. When plucking or strumming the strings, a very light string attack requires little or no relief, whereas very aggressive string attack may warrant greater relief.

Check for Neck Bow
Check for Neck Bow

Many guitars, upon inspection, have necks that appear to suffer from excessive bow, often forward but sometimes backward. Excessive back (convex) bow will cause the strings to lay on the fretboard against the frets, making the guitar unplayable. On guitars whose necks have a single action truss or compression rod, it may be possible to simply loosen the tension on the rod and allow the strings to pull the neck forward enough to counteract the back bow. If the neck is equipped with a dual-action truss rod, it is usually possible to mechanically bow the neck forward. If the neck continues to curl backward, the condition of the neck will need to be addressed, first.

Excessive forward (concave) bow, a visible curling forward of the neck, will raise the action to a point where the guitar quickly becomes unplayable. Most modern guitar necks are equipped with a means of countering the pull of the strings on the neck, and an excessive forward bow may be able to be corrected by tightening the truss rod in the neck. If such corrections fail to make the guitar playable, a neck reset is probably in order.

It is not unheard of to find a guitar neck in which the appearance of a twist has been deliberately introduced by the builder for ergonomic purposes. I am unaware of any large manufacturers/factories doing this, but that could change. Should you own such a guitar you may want to ignore this next paragraph.

Occasionally, the wood of a neck will twist enough that one side or the other ends up raising the strings much higher than it should. Looking down the fretboard from one end of the guitar or the other and comparing the plane of the headstock/nut against the plane of the bridge/soundboard should help to confirm or alleviate any suspicion of twist. In some cases, the bridge has been planed or sanded into a wedge shape, either originally by design or during some re-design, intervention, repair, etc. If so, it is the plane of the soundboard alone, not the top of the bridge, that the plane of the nut should be compared to in order to determine if we are dealing with neck twist, or not.

Check for Neck Twist at the Nut
Check for Neck Twist at the Nut ...
Check for Neck Twist at the Saddle
... by comparing with the plane of the soundboard

Severe twist may or may not be correctable. In lieu of straightening or replacing a twisted neck, sometimes cleverly messing with the geometry of the neck, body, bridge, and saddle is sufficient to keep a guitar playable without killing the sound. Sometimes the fretboard can be replaced and planed to counter a twist. Sometimes.

2. Neck Geometry

Does the guitar need a neck reset?

For a lengthy discourse on this very topic, please see my article titled » Neck Resets.

Seven (7) assessments will provide me with the information I need to know whether a neck reset is necessary, or not:

1. Establish a flat fretboard plane
2. Assess and address bridge lift (if any)
3. Address bellying
4. Assess saddle height
5. Measure overall string height in front of the bridge
6. Address nut slot height
7. Measure string action height

If a neck reset is determined to be necessary, I consider it best to resolve that issue prior to continuing with Setup steps. Efforts to stave off a neck reset, while certainly doable, are compromises at best, and typically result in more work needed, later.

3. Action (String height at the 12th fret)

Action is defined here as the height of the strings above the frets. Action is an informative indicator regarding what is going on with my guitar and is the leading reason behind the need for the majority of neck resets. When my guitar is uncomfortable to play, or perhaps even unplayable, due to high string action, I need to sequentially walk through the steps necessary to return the instrument to playability. It is time for a proper setup.

Before I ever even consider issues such as fret height, nut slot depth, or saddle height and completely independent from issues such as bellying, bracing failure or collapse, let alone prior to beginning any dramatic neck alterations which will include neck condition, neck joinery method, neck geometry, etc., it is necessary to establish a reference against which changes can be measured. An ideal reference is a flat fretboard. While it may not be possible, or even preferable (for reasons I will explain, next), to force the fretboard into a perfectly flat surface, I need to be able to reference as close to a flat plane as possible across the length of the fretboard before I can proceed. I say fretboard, not neck, not even frets, as the surface of the board is my reference.

Assuming I know what I'm doing, if all of my attempts to complete a proper setup on my guitar result in the strings either laying on the fretboard buzzing (action is much too low), or being so far away from the fretboard that they cannot be fretted (depressed to make contact with the metal frets) without significant effort and corresponding discomfort/pain (action is much too high), it is highly probable that my guitar requires a neck reset.

There are potentially four (4) adjustable components on my guitar that are considered by many to be applicable to addressing string action height:

Action - String Height Above Fretboard
Action - String Height Above Fretboard

Action item 1. Truss rod - I have written rather extensively about truss rods, the various types and their functionality in my article » D-Tube by DragonPlate - Truss Rod Alternative. In summary, most modern steel string acoustic guitars are fitted with adjustable truss rods that run beneath the fretboard from the nut to the neck heel. The primary function of a truss rod is to counter the tendency of the neck to bow forward. This is not to be confused with a neck stiffener, which serves only to resist forward bow, but provides no mechanical adjustability.

A compression rod is (or, in the case of older Guild 12 strings, twin compression rods are) pressed into a concave bow in deep slots in the neck, fixed into the neck heel, and threaded into a recess in the headstock. Tightening a nut/washer combination against the end grain of the neck forces the rod to straighten which, in turn, forces the neck to bow backwards. Loosening the nut (re)submits the neck to the tension of the strings and (typically) results in a forward bow. More or less.

An independent single-action (or 1-way) truss rod secures a threaded rod to a metal beam that sits as a unit in a single, shallow channel in the neck beneath the fretboard. Unlike a compression rod, it is not attached to the neck. A socket on one end may be installed at the headstock or accessed through the soundhole, depending on the builder's preference. Tightening the rod (by turning the socket clockwise) will, as with the compression rod, induce a back bow. Turning the socket counter-clockwise will, as with the compression rod, allow the string tension to pull the neck forward.

A dual-action (or 2-way truss rod) also installs in a guitar neck as an independent component, just like the single-action (or 1-way) version. However, unlike both the single-action truss rod or a compression rod, a dual-action truss rod may also be used to deliberately bow the neck forward. Why would anyone incorporate such a design when, seemingly, the strings are working to pull the neck forward? Necks having dual-action truss rods are typically built much stiffer than their predecessors (for example, carbon fiber rods are often installed on either side of the truss rod channel). Having the ability to "dial in" the desired fretboard flatness is perceived by many to be essential.

This adjustability highlights a secondary function of the dual-action truss rod, that of inducing relief, a small but deliberate forward bow in the fretboard that some builders and/or players feel is necessary to mitigate string-to-fret contact.

It is important to note that, in the case where a guitar with uncomfortably high action is determined to be suffering from too much forward bow, and that guitar is fitted with some form of adjustable truss rod, the forward bow can be reduced (or eliminated) and the action lowers proportionally.

While that may be all a player needs to restore a guitar to functionality, please realize that adjusting string action height is NOT the role of the truss rod. More on this, later.

Action item 2. Saddle - Unlike a violin or banjo, nearly all acoustic guitars feature a saddle that is fitted into a slot in the bridge. As such, it can readily be replaced when worn, or with a different material for tonal purposes. If a player has a particular action preference, and assuming the fretboard is already set to proper relative flatness, the saddle is often seen as the adjustable component to be used to raise or lower the string height.

The strings are set extremely close to the tops of the frets nearest the nut, sometimes clearing the first fret by as little as 3 to 5 thousandths of an inch. However, that distance increases exponentially as you move up the fretboard. Action is typically measured at the 12th fret, where the gap between the top of the fret and the bottom of the string may easily be 30 x greater. In cases of extremely high string action, that gap may be 50 or 60 x greater at the 12th fret than it is at the 1st fret.

Lowering the saddle height is usually accomplished by sanding or filing the bottom of the saddle in order to avoid altering any deliberate contouring for intonation purposes. Before breaking out the sandpaper, however, take a moment to familiarize yourself with some geometry. We are measuring action height at a point half-way between the nut and the saddle (typically the 12th fret). If we wish to lower the action by a said amount at that 12th fret, we must reduce the height of the saddle by that desired amount times a factor of 2. As an exaggerated example, if I wanted to lower my action (at the 12th fret) by 1/8" I would need to remove 1/4" off the height of the saddle (1/8" x 2)! If my guitar has really high action at the 12th fret, you may imagine that I am likely to quickly run out of saddle material in my attempts to make the guitar comfortable to play.

More importantly, viewing the saddle simply as a string height adjustment component ignores a significant factor that governs the overall sonic output of any given guitar: the overall string height measured in front of the bridge. More on this, later.

Action item 3. Bridge - So what if I have adjusted my fretboard to be as flat as it can go, and I have lowered my saddle down to as far as it can go, but I still have a little bit too high of a string action? Is there anything left for me to adjust? A more serious modification occasionally made in an attempt to get the string height as low as possible (not recommended, by the way) involves reducing the height of the bridge by planing, shaving and/or sanding. The idea behind this is that, in order for me to have enough saddle emerging from the surface of the bridge to get a solid string connection on, knowing I cannot raise the saddle any higher (my action height is still too high), I need to lower the bridge height.

Will resorting to such drastic measures make a guitar playable, again? Perhaps, but such playability comes at a price. The bridge is an external brace on my soundboard. Altering its size will alter the tone of my guitar. Rarely does reducing the height of an existing bridge yield positive sonic results.

Action item 4. Frets/Fretboard - Since most action height adjustment efforts involve reduce the distance between the plane of the strings and the surface of the frets, could we not simply raise the frets up closer to the strings? Installing taller frets is a viable method to attempt to return a guitar to playability. This does not work for everyone, though, as A.) We are talking about extremely small differences in height that are often insufficient to overcome extremely high action conditions, and B.) A radical adjustment in playing technique is required for the tallest of frets, and most players don't care for the "feel." It has never been my experience, nor have I ever been told by a player, that taller frets makes for a more comfortable fretboard.

A similar solution involves swapping out the fretboard with a thicker one, one that perfectly resolves both the string action height issue as well as maintains the payer's preference for fretwire. The potential downside to this is the resultant increase in overall neck depth (or "thickness"), where my favorite skinny neck nows feels chunky, along with a slight increase in weight.

If, after taking these four (4) factors into consideration, I am still left with uncomfortably high string action, what next?

4. Frets and Fretboard

Some necks are simply not straight to begin with; as in, they cannot even be forced into a flat condition. Such necks need to be addressed, separately, as a neck reset is not the proper solution. Before giving up on a troublesome neck, it is worth investigating whether it is the neck or the fretboard that is causing the problem. Sometimes a fretboard can be replaced more readily than an entire neck.

Removing the frets and flattening the fretboard lets me literally start from a level playing field. This is the right time to address the condition of the overall fretboard (such as its overall thickness), adjust the radius, increase or reduce fall-away and make decisions regarding the optimal fret height and fret material for the replacement frets.

5. Nut Slots and Saddle Height

Once I know my neck/fretboard is straight, my next step in setting up proper action is to address the nut slots. This step pertains to fretboards whose nut acts as fret zero. The difference between a guitar that feels like a wire cheese slicer on my fingertips and a fretboard that "plays like butter" starts at the nut slots, specifically, in the distance between the top of the first fret and the bottom of the string as it rests in its respective slot in the nut. There should only be enough distance (the slots should only be close enough to the fretboard) to prevent the strings from resting on the first fret. A common test that can be conducted without using measuring tools (such as a dial indicator or feeler gauges) is to depress each string against the 3rd fret and "tap" each fretted string against the 1st fret. I am hoping to see only the slightest gap between the fretted string and the top of the 1st fret. Anything more than that is an opportunity to lower the nut slot.

Saddle height is not arbitrary, at least not if I am wanting my guitar to be all it can be. Reaching for the sandpaper to shorten the height of the saddle, in an effort to lower the action to make my guitar easier to play, is rarely the best solution if I am expecting maximum volume and optimum tone from my guitar. Instead, I want to achieve optimum height of the strings off of the soundboard in front of the bridge. That means that establishing the string height for player comfort is the primary role of the neck geometry, not the saddle.

To that end, you may acknowledge the benefits of having an easily adjustable neck, such as a bolt-on neck, where the neck joint can quickly be altered and shimmed. Action can be adjusted at the neck joint, leaving the saddle and bridge to perform at their respective peaks.

Let's assume my neck/fretboard is flat and the strings are properly seated in their respective nut slots (that have been filed as low as they can go without buzzing).

I have created an illustration to demonstrate the various heights involved:

a = Overall string height (in front of the saddle)
b = Bridge height
c = Saddle projection above the bridge / Saddle slot depth
d = Overall saddle height

I set a goal of at least 1/2" (or 12.7 mm) for my overall string height, measured in front of the bridge. I want my saddle slot depth to be 1/2 the height of the saddle, but not exceed 1/2 the height of the bridge. This means that the section of the saddle projecting above the bridge is as tall as the saddle slot is deep.

Bridge, Saddle and Saddle Slot
Bridge, Saddle and Saddle Slot

Here are two solutions, one imperial and the other metric:

Imperial
a. Overall string height: (goal) 0.5", (actual) 0.52"
b. Bridge height: 11/32"
c. * Saddle height above bridge/Saddle Slot depth: 11/32"
d. Overall Saddle height: 11/64"

Metric
a. Overall string height: (goal) 12.7 mm, (actual) 13.5 mm
b. Bridge height: 9 mm
c. * Saddle height above bridge/Saddle Slot depth: 4.5 mm
d. Overall Saddle height: 9 mm

* NOTE: If using USTs, the slot will be deeper by the thickness of the pickup (measure from the top of the pickup to the top of the bridge).

6. Torque and Overall String Height

The shortest distance between two points is a straight line, which describes a string at rest between the nut and the saddle. When a string is fretted, that straight line is altered as the string is deflected from its resting path to make contact with the fret wire. When strummed or plucked, the string will actually swing back and forth across that straight line.

Do you believe that the string is simply stretching, or lengthening, as it is pushed or pulled away from its straight path at rest?

Imagine yourself holding the end of a large, long rope that you have tied to a tree. Stretch it taut and have a friend run and throw himself at the rope in an attempt to get you to break your grip. The rope doesn’t stretch, at least, nowhere near as much as you, the holder of the end of the rope, move forward, toward the tree. As you then return to your original position, leaning or stepping backward, the rope is pulled straight again. Since your friend is hanging onto the rope, that momentum has them then pulling the rope in the opposite direction, which pulls you forward again. Naturally, you counter and pull the rope straight again, and so on.

When a guitar string is plucked (pulled away from that straight line), it is more the guitar that is making up for the change in distance than the string. The entire guitar is moving in response to the oscillations of the string(s), including the neck, neck block, soundboard, body shell and, in particular, the bridge. This is occurring at extremely high speed, and the movement is very small. But it is really happening.

Torque is a description of rotational force or, perhaps better, torque is the rotational equivalent of linear force. Torque is the ability of a force to produce a rotation around an axis. That axis is the crest of the saddle.

Torque and Overall String Height
Torque and Overall String Height

There must be sufficient torque at the intersection of string and saddle to maximize the string energy transferred via the bridge to the soundboard. Too much torque, applied by the addition of too heavy a gauge of string or by too great a height off the soundboard, risks ripping the bridge (along with the soundboard and bridgeplate beneath it) right out of the guitar! Should the bridge remain affixed, there is a strong likelihood that such a combination will result in overdriving the soundboard (such as may occur when supplying a loudspeaker with too much amperage). Too little torque, such as we find in guitars using too light a gauge of strings for their particular configuration of bracing, soundboard, bridge and saddle, and/or whose saddles are buried in their bridge slots, results in a weak output.

Both dynamic and static torque are at work on an acoustic guitar bridge. Dynamic torque references acceleration, or how quickly the bridge can be made to move (or vibrate). Imagine beginning a bicycle race at the bottom of a hill and the initial effort required to move your bicycle from its resting position. Understanding this analogy, we would advocate for lightweight bridges. Static torque refers to how an object in motion wants to stay in motion. On a level road it is downright therapeutic to pedal your bicycle once it is underway. Understanding this analogy, we might advocate for slightly heavier bridges, as the additional weight lends itself to continuing in motion once it is successfully set in motion. We may only be talking about a matter of +/- 15 grams difference between the two examples, but it is enough difference to affect the sound.

7. Break Angle

Break angle is a term that refers to the angle at which the string, emerging from the bridge (or even a tailpiece, such as may be found on an archtop guitar), "breaks" across the saddle as it continues its path to the nut. There is an additional break angle that can be identified as the string leaves the back of the nut in a trajectory to the post of the machine head (tuner), but that is a separate topic. Having sufficient break angle as the string leaves the back of the saddle is essential, but probably not for the reason you are accustomed to hearing.

Too shallow of an angle (as in "no" angle) permits the string to bounce across the crest of the saddle. By contrast, too sharp of an angle behind the saddle may result in frequently broken strings. If the saddle extends far enough out of the slot, an extremely sharp break angle may physically break the saddle or, more commonly, may split out the front of the bridge.

Break Angle (illustration courtesy of Haze Guitars)
Break Angle (illustration courtesy of Haze Guitars)

Ramping slots between the bridge pin holes and the back of the saddle, in addition to improving the coupling between the ball end of the strings and the bridgeplate, will increase a shallow break angle. In an all-too-common scenario, you are able to get that break angle seemingly just right, and your volume/tone actually improve a bit, but you now begin to experience some buzzing as the strings are touching the front of the bridge, due to the saddle being too low ("buried") in the slot.

In order to experience maximum sonic output from such a typical acoustic guitar, the measured angle of the string breaking over the saddle is of much less importance than is the overall height of the string off of the soundboard. The torque applied from sufficient string height will actually set the bridge into motion in response to the force applied (energy transmitted) as the string oscillates. Break angle serves to lock the string down over the crest of the saddle, such that any shifting and rolling from side to side on the part of the string(s) is eliminated or minimized. Rather than being wasted, maximum energy can then be transmitted down into the bridge (and out across the soundboard).

8. Bridge Shaving

Shaving a bridge refers to planing, scraping, or sanding material off the top surface of an acoustic guitar bridge, typically while it is still attached to the guitar.

Why do such a thing?

1. To deliberately alter the tone/volume of the instrument.
2. To delay a neck reset, and subsequently (wittingly or not) live with the altered tone/volume.

If you are still with me at this point, I trust that you will have a better understanding regarding optimal overall string height. Unless a gross mistake was made during construction, and some monstrously tall bridge was installed, and planing the bridge will keep it close to that 11/32″ (or 9 mm) height range, and the saddle height above the bridge will be close to that 11/64″ (or 4.5 mm) range, such that total string height is NOT LESS than 1/2″ (or 12.7 - 13 mm), and string action is perfect for your style of playing . . . it is probably not in you or your guitar's best interest to further lower the bridge height.

The bridge of my guitar is an external brace, adding stiffness and mass to the soundboard. In conjunction with the bridgeplate, the bridge is a fixture, providing me with a means of attaching the strings, as well as holding the saddle in place. The bridge is an acoustic coupler, transmitting the kinetic energy of the plucked and oscillating strings across the soundboard. Altering the mass of the bridge will alter the sound of the guitar, its volume and tone.

As with the saddle, bridge size (or overall "mass" including height, width, weight, and density) is not arbitrary. The bridge must be sized correctly to perform its tasks well. Too large or too small of a bridge will make for poor sound output. On center hole, X-braced guitars, the bridge is sized to rest atop the lower legs of the X. The mass of the bridge is relative to the responsiveness of the internal bracing and soundboard, as well as the tension of the strings. A heavier bridge may require a heavier gauge string to set it into motion. A heavier gauge string will result in greater tension, and put greater demands on the bracing and the soundboard, which must be designed to support the extra load.

"But my guitar repair guy planed my bridge, made a new saddle, ramped the bridge pin holes, put on a new set of the world's greatest strings and now my guitar sounds better than it did before!"

I am sure it does. And it would sound even better, like it was originally designed to sound, had he FIRST established optimal string height, THEN reset the neck so that the action was perfect at that new target string height!

9. Bridge Lift

Bridge lift describes a visible gap between the soundboard and the back of the bridge. Such a gap may or may not require attention. Most guitar bodies have a finish applied prior to attaching the bridge. For a proper bond, the bridge needs to be glued to the raw wood surface of the soundboard, not the surface of the finish. To that end, the finish is either carefully removed or prevented from ever being applied in the area where the bridge will lay. It is quite common to leave a small border of finish around the periphery of the bridge, just enough for the bridge to rest on and provide for a clean visual intersection, as opposed to removing finish to the outside edge of the bridge, which would reveal an unsightly trace line all around the bridge. If (or as) the bridge rocks or tilts slightly forward, and depending on several other factors, including how wide that border of finish under the backside of the bridge is, a gap may or may not appear along the back edge, and that gap may or may not be stable for the life of the instrument.

Bridge Lift
Bridge Lift

Bridges should not require re-gluing. By contrast, fret wear is expected, but having a bridge come unglued should not be considered a common maintenance item.

A significant gap behind the bridge is an indication that something has gone wrong, either as a result of a slow process of failure due to poor materials or construction in the very beginning, or perhaps more sudden damage (like leaving a guitar in the hot car or subjecting an instrument to undue moisture). The strings will likely be raised much higher off the fretboard than they should be. In the simplest of cases, where glue failure is due to insufficient glue and/or loose bracing, glue and clamping may be all that is needed to restore a guitar to playability. In some cases, such as an oily bridge that glue is refusing to bond well with, or too large of a finish border beneath the bridge, it may be better to completely remove the bridge in order to first address those issues. The above are best case scenarios. It may be that the soundboard is too thin or is in process of shearing due to severe grain run-out, or the bracing is simply insufficient to prevent the buckling that is contributing to the bridge lift. More dramatic steps may be necessary to mitigate a catastrophe.

It bears repeating that the thickness of an acoustic guitar bridge, also referred to as its height, is not (rather, should not be) an arbitrary measurement! Employing a production-minded technique certainly not unique to Guild, many guitar makers of yesteryear assembled their instruments by first attaching the necks to the body, and then selecting/making/modifying a bridge to fill the space between the soundboard and the plane of the fretboard (already established by the attached neck). With bridge height being the only criteria, it is easy to understand (years later) why the same model instrument could have such significantly audible distinctions from siblings produced on the same assembly line.

The bridge of an acoustic guitar is a multi-functional component. The bridge is (typically) responsible for pinning the strings in place. The bridge supports the saddle. The bridge, the only exterior brace on the soundboard, in conjunction with the bridgeplate (for pinned bridges), forms a unit that is responsible for transmitting kinetic energy generated by the plucked string(s) onto and across the soundboard, which is sandwiched between the two. It is crucial for the mass of a given bridge (taking into account the mass of the bridgeplate beneath it) to be sufficient to drive the top, to set the soundboard in motion. It is quite easy to rob the sonic life out of a guitar by adding or modifying a bridge that is improperly sized. Too small or too light a bridge will produce a very weak output.

Likewise, too large/too heavy of a bridge can either act to dampen transmitted energy or completely overdrive the top.

Assuming the goal is to achieve the maximum sonic potential of a given soundboard, a crucial factor in determining the optimum size/mass of its bridge/bridgeplate is the overall stiffness of that soundboard after bracing. Overall soundboard stiffness will be determined by the material(s) used in the construction of the soundboard, as well as by the pattern, dimensions, and stiffness of the bracing.

The bridge must first be matched to the soundboard on which it will reside, and then the neck geometry can be determined. Not vice-versa.

If, in order to stave off the apparently inevitable neck reset and to keep the instrument playable, overall string height has been lowered by reducing the bridge’s height (by planing or "shaving"), it is quite possible that the bridge is now undersized. This typically translates into a quieter, lackluster sounding guitar. Efforts to improve the tone and/or volume, such as increasing the string gauge (moving from lights to mediums, or from mediums to heavy gauge), replacing plastic bridge pins with bone, or replacing bone bridge pins with brass or titanium, will be short-lived solutions. The fix is in - to restore such a guitar it will now be necessary to remove both the neck and the bridge, pair a new bridge (and possibly bridgeplate) with the soundboard, and reset the neck.

10. Bellying and Brace Assessment

Bellying describes a condition where the lower bout section of the soundboard, the part directly behind the bridge, is pulled markedly upward by the tension of the strings. This is typically the result of the bridge rocking slightly forward, and can be due to several factors:

• Glue failure between the soundboard and the X-brace
• Insufficient bracing in front of the bridge, causing it to plough downward
• Insufficient bracing behind the bridge, permitting it to lift upward
• Too thin of a soundboard
• Some combination of any of the above

Bridge lift may accompany bellying, though not always. Is bellying ever acceptable? More than one luthier thinks so, with the maxim, "No belly, no tone" being echoed by both pros and novices, alike. If so, how much bellying is “too much?” Slight to modest bellying is simply the result of the pull of the strings on the bridge and the related structural integrity of a given guitar that resists the tendency of that string pull to fold the instrument in half. So long as everything stays in place, all is well and may remain so for the life of the instrument.

However, if the belly increases, it is quite possible that something is (or several "somethings" are) wrong. The string action will have been raised, as either the bridge is now tilting forward like a surfer catching a wave, or the entire soundboard is lifting. Resetting a neck on such an instrument may be a short-lived solution, as that belly may not be done lifting. Prior to assuming a neck reset is immediately necessary, it may be prudent to first address the belly bulge. Where bellying is the result of components having shifted away from their original positions, it is possible to "flatten" that belly using heat with a series of cauls. Sometimes bracing can be (or should be) re-glued and this is sufficient to deflate a bulging belly. Where bellying is the result of insufficient bracing and/or a soundboard does not have sufficient stiffness to stay flat, more drastic measures may be called for. Only after addressing bellying should you proceed with a neck reset.

Contrast the Fender Stratocaster with the Gibson Les Paul. Again, the longitudinal axis of the body is shown in by the green line, and the red line follows the string path. Note how the neck deviates from the longitudinal axis of the body, and the headstock deviates from the longitudinal axis of the neck. Compared with the Strat, the "chord" formed by the string path in relation to the longitudinal axis of the neck/body unit demonstrates a sharper angle of incidence.

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