- May 6, 2004
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- Independent Instrument Technician - Retired
Here's a look at neck geometry. It illustrates why there is one nut height that is optimum for any given bass and how a degree of relief can improve playability beyond a truly flat fingerboard.
This illustration is based on a few assumptions. First is that for any given player on any given bass, there is an optimum setup condition that provides the best "playability". I will define "playability" as ease and consistency of playing the instrument all up and down the neck. That is for any given pluck of the string with a given force, the same degree of fret rattle occurs no matter where the string is fingered (in most cases we look for no buzz at all unless we really dig in).
Secondly, not only should that degree of buzz be consistent up and down the neck, it should also be consistent from string to string. For this illustration I will be considering only one string, but the same would apply across the board as well as up and down it.
So I am assuming we are trying to achieve a playability with action that normally does not produce fret buzz. To achieve this buzz free condition all up and down the neck, we must have a certain amount of clearance between the next fret and the string regardless of where we are fretting. That is, if we are fretting at the second fret, there must be a certain amount of clearance between the third fret and the string. And let's assume we have determined exactly what that clearance needs to be to avoid buzz. THat's probably the amount of clearance we need at the "next" fret regardless of where were are fretting.
So now we can plot it out. For simplicity and clarity my illustration has only a few frets, evenly spaced, with a bridge higher than the fret tops (or else to wold buzz everywhere) and a nut height that we will determine from the geometry. So here is the base illustration I will use:
Distances and sizes are exaggerated here for clarity of illustration since the real clearances are so small it would be impossible to see what I am talking about. The string is represented by the red line, while the blue and green triangles are the nut and bridge respectively. I am using 4 frets in this illustration - that's all we need. They are the triangles numbered 1, 2, 3, and 4.
Now let's assume we have the bridge height set just right to be as low as it can be without buzzing. Let's see what that looks like when we fret at the 3rd fret:
The arrow over the 4th fret shows the amount of clearance between the fret and the string. And since we have set this to be optimum, it's the same clearance we should have over the 3rd fret when fretting at the 2nd. So let's plot that amount of clearance and see where the fret top needs to be:
Clearly, to maintain a consistent clearance, we need to raise the 2nd fret. So in the following illustration I have raised the second fret to give the right clearance at 3, and I am now fretting at the 1st fret:
And once again I need to raise the 1st fret to provide the right clearance at the second. So in the next illustration I have raised the 1st fret to give the proper clearance at the second.
Now, by extension I can determine how high the nut has to be to give a consistent clearance at the first fret:
So to maintain consistent clearance, the slot in the nut should be cut so the string sits in it to the same depth as the red line. So now we have a plot that shows the geometry that will produce consistent clearances as we fret up and down the neck. And an interesting bit of information surfaces - take a look at the line we get when we connect the fret tops:
It's a gentle curve. We call it relief. Except we generally get that curve by controlling the bend in the neck, not by altering the height of individual frets. Geometrically it's equivalent.
Now this tells a story, but it's not entirely accurate. First it's greatly exaggerated as I indicated earlier. And on our instruments the frets are not evenly spaced. And you actually need less clearance as you go up the neck because the string excursion lessens as you go higher. But those factors counter each other and the net effect is the same as illustrated.
I hope this helps in understanding why I say there is only one correct nut height for any given bass. The exact height will depend on the string height at the bridge, the height of the frets, the amount of relief in the neck and the desired fret-to-string clearance. All of those elements are related as it pertains to the "action" of the instrument. And it should be clear that any nut height other that what I illustrated is either too low to give consistent clearance, or unnecessarily high, which will lead to intonation issues on the first few frets. And the illustrations also show why the proper amount of relief contributes to the optimum playability off the instrument.
I invite discussion.
This illustration is based on a few assumptions. First is that for any given player on any given bass, there is an optimum setup condition that provides the best "playability". I will define "playability" as ease and consistency of playing the instrument all up and down the neck. That is for any given pluck of the string with a given force, the same degree of fret rattle occurs no matter where the string is fingered (in most cases we look for no buzz at all unless we really dig in).
Secondly, not only should that degree of buzz be consistent up and down the neck, it should also be consistent from string to string. For this illustration I will be considering only one string, but the same would apply across the board as well as up and down it.
So I am assuming we are trying to achieve a playability with action that normally does not produce fret buzz. To achieve this buzz free condition all up and down the neck, we must have a certain amount of clearance between the next fret and the string regardless of where we are fretting. That is, if we are fretting at the second fret, there must be a certain amount of clearance between the third fret and the string. And let's assume we have determined exactly what that clearance needs to be to avoid buzz. THat's probably the amount of clearance we need at the "next" fret regardless of where were are fretting.
So now we can plot it out. For simplicity and clarity my illustration has only a few frets, evenly spaced, with a bridge higher than the fret tops (or else to wold buzz everywhere) and a nut height that we will determine from the geometry. So here is the base illustration I will use:
Distances and sizes are exaggerated here for clarity of illustration since the real clearances are so small it would be impossible to see what I am talking about. The string is represented by the red line, while the blue and green triangles are the nut and bridge respectively. I am using 4 frets in this illustration - that's all we need. They are the triangles numbered 1, 2, 3, and 4.
Now let's assume we have the bridge height set just right to be as low as it can be without buzzing. Let's see what that looks like when we fret at the 3rd fret:
The arrow over the 4th fret shows the amount of clearance between the fret and the string. And since we have set this to be optimum, it's the same clearance we should have over the 3rd fret when fretting at the 2nd. So let's plot that amount of clearance and see where the fret top needs to be:
Clearly, to maintain a consistent clearance, we need to raise the 2nd fret. So in the following illustration I have raised the second fret to give the right clearance at 3, and I am now fretting at the 1st fret:
And once again I need to raise the 1st fret to provide the right clearance at the second. So in the next illustration I have raised the 1st fret to give the proper clearance at the second.
Now, by extension I can determine how high the nut has to be to give a consistent clearance at the first fret:
So to maintain consistent clearance, the slot in the nut should be cut so the string sits in it to the same depth as the red line. So now we have a plot that shows the geometry that will produce consistent clearances as we fret up and down the neck. And an interesting bit of information surfaces - take a look at the line we get when we connect the fret tops:
It's a gentle curve. We call it relief. Except we generally get that curve by controlling the bend in the neck, not by altering the height of individual frets. Geometrically it's equivalent.
Now this tells a story, but it's not entirely accurate. First it's greatly exaggerated as I indicated earlier. And on our instruments the frets are not evenly spaced. And you actually need less clearance as you go up the neck because the string excursion lessens as you go higher. But those factors counter each other and the net effect is the same as illustrated.
I hope this helps in understanding why I say there is only one correct nut height for any given bass. The exact height will depend on the string height at the bridge, the height of the frets, the amount of relief in the neck and the desired fret-to-string clearance. All of those elements are related as it pertains to the "action" of the instrument. And it should be clear that any nut height other that what I illustrated is either too low to give consistent clearance, or unnecessarily high, which will lead to intonation issues on the first few frets. And the illustrations also show why the proper amount of relief contributes to the optimum playability off the instrument.
I invite discussion.
