Thoughts on Neck Relief
Neck relief is, I believe, a very misunderstood aspect of guitar setup. How many times have you heard these statements: "Action’s too low? Just give it some neck relief", "Bluegrass players need some neck relief", "Action’s too high? Reduce the neck relief". Let’s examine some of these statements, but first let’s define "neck relief". Relief describes the bow of the neck. A guitar neck is typically not perfectly straight, but has a dip about mid-way- this is relief. I measure it by putting a capo on the 1st fret, holding down the string on the fret where the neck meets the body- thus creating a straightedge with the string- and measuring the gap between the bottom of the low E and the 7th fret. I use feeler gauges (.002" - .025", stacked for thicker measurements) under good lighting to do the actual measuring. I use the 7th fret just for consistency and because if you hold the string at the 14th fret (as with most acoustic guitars), the 7th fret is halfway. On electric guitars, you’ll be holding down the 17th fret or thereabouts, but most of the neck bow still occurs around the 5th-7th frets. Another term we should define right now is "action"- this is simply the clearance between the bottom of a string and a fret. A high action means you have to push the string down farther to contact the fret than on on a low action
Why do "bluegrass players need neck relief"? The presumption is usually that bluegrass players only play in 1st or 3rd positions. Since the maximum amplitude of vibration is at the halfway point, the idea is that adding some neck relief will allow a "pocket" of higher action, created by neck relief, in which the string will vibrate. While that may be true when playing at the 3rd fret, what happens when you use a capo, especially at the 4th fret? Suddenly, your bluegrass player is playing "up the neck"!
Neck relief is not independent of the other two action adjustments, namely the nut height and 12th fret action. If you change neck relief and don’t touch the nut or saddle, the action at both the 1st and 12th frets will also change. Therefore, simply using neck relief to adjust action is not usually a good idea. The only time I’d consider it is when the neck relief is adjusted within some pre-specified parameters, such as "between .006" and .010"". Within whatever range you decide on, yes, you can use the truss rod to fine tune action.
I had several questions about neck relief.
First, how does neck relief affect the "next fret action"? If you fret the 3rd fret, what is the clearance at the 4th fret, and if you fret the 5th fret, what is the clearance at the 6th fret? The string is mostly like to buzz if the next fret action is too low.
Second, what happens behind the fretted note? If you fret the 5th fret, what happens to clearance at the 3rd fret? A lot of buzzes actually happen behind the fretted note.
Third, what happens to mid-neck actions when the neck relief is changed? We’re usually concerned with the 12th fret actions, but what happens at the 3rd, 5th, 7th, and 9th frets? The action here greatly affects mid-neck playability and feel.
Fourth, what happens to the "mid-way" action? When the string is fretted at the 3rd fret, what does the action at the 12th fret look like? When fretted at the 5th fret, what happens to the action at the 15th fret ? Remember, the maximum amplitude occurs at the half-way point and the half-way point depends on where you fret.
To find out, I recruited my James Burton Standard Telecaster. I chose this guitar because the truss rod adjusts at the nut (easy to get to), the neck responds well to the rod's adjustments, and the adjustable saddles made it easy to change the 12th fret actions. I've verified or suspected many of these measurements on other guitars, but this was the first time I've done them all on one guitar at one time.
(Click here to skip the evidence and go directly to the Conclusion)
First, I looked at the effects of neck relief on various actions. I used the truss rod to adjust the neck for 3 different neck reliefs: .008", .012", and .018". After setting the neck relief, I set the 12th fret action to .096", by adjusting the saddles. Then, I measured the action at various places. Here are those figures: (NOTE: don't be intimidated by all these figures- simply compare actions for a given fret. Compare the actions of Fret 1, the actions of Fret 2, etc.)
| Action | |||
| Fret | R = .018" | R = .012" | R = .008" |
1 |
0.028 |
0.027 |
0.025 |
3 |
0.056 |
0.052 |
0.050 |
5 |
0.072 |
0.068 |
0.066 |
7 |
0.084 |
0.084 |
0.080 |
9 |
0.093 |
0.094 |
0.088 |
12 |
0.096 |
0.096 |
0.096 |
Notice that the mid-neck actions are quite a bit higher with greater neck relief. This is no big surprise, but it is surprising how fast the higher action comes into play- by the 1st fret and quite noticeably by the 3rd fret. Note that the 12th fret action is identical in each case- it's the constant in this experiment.
Okay- what happens to the "next fret" clearances? To measure this, I put a capo on the fret and measured the clearance of the string over the next fret:
| Next Fret | |||
| Fret | R = .018" | R = .012" | R = .008" |
1 |
0.016 |
0.014 |
0.014 |
3 |
0.012 |
0.014 |
0.011 |
5 |
0.012 |
0.012 |
0.010 |
7 |
0.012 |
0.012 |
0.010 |
9 |
0.008 |
0.010 |
0.011 |
12 |
0.008 |
0.010 |
0.011 |
Notice that the greater relief does indeed give greater next fret clearance, but only for the lower frets. As you work up the neck, the next fret clearances get lower and lower, faster. With less neck relief, the next fret clearance is much more consistent and is considerably higher at the 9th and 12th frets. .003" may not seem like much, but it can mean the difference between buzzing or not.
What’s happening behind the fretted notes? Here, when the capo was on the 3rd fret, I measured the 1st fret- after that, I measured the 3rd fret :
| Previous Fret | |||
| Fret | R = .018" | R = .012" | R = .008" |
1 |
|||
3 |
0.008 |
0.008 |
0.006 |
5 |
0.008 |
0.006 |
0.006 |
7 |
0.014 |
0.012 |
0.010 |
9 |
0.018 |
0.014 |
0.012 |
12 |
0.020 |
0.018 |
0.016 |
Now here’s a possible cause of buzzing- the clearance is less with less relief, and it’s certainly possible that some "back buzzing" might occur. However, the solution to this is easy: raise the nut. Look at the first table of figures comparing actions- if you can handle a 1st fret of action of .028" with relief of .018", you can certainly handle it with lower relief. Raising the nut therefore would increase the "previous fret" action enough to probably stop buzzes. Or you might go the other way and lower the nut so that the string sits closer to the frets and vibrations die before they have a chance to buzz. Certainly, I think .028" is pretty high and I normally run .020"- .016" of actual 1st fret clearance (that is, measured with no capo).
And finally, what about the mid-way actions? Here, I put the capo on a fret and then measured the action roughly half way to the saddle (this would be the point of maximum vibration amplitude). This "half-way" point changed, of course, depending on which fret was capoed.
| 1/2 way to saddle | |||
| Fret | R = .018" | R = .012" | R = .008" |
1 |
0.076 |
0.076 |
0.076 |
3 |
0.066 |
0.074 |
0.071 |
5 |
0.064 |
0.068 |
0.071 |
7 |
0.060 |
0.066 |
0.068 |
9 |
|||
12 |
|||
Here we see that the same 12th fret action with less neck relief clearly gives equal or greater mid-way action, all the way up.
Conclusion so far:
Given the SAME 12th fret action, less neck relief will give equal or greater next fret clearance, equal or greater mid-way action, lower mid-neck action, and lower behind the fret action. The latter could cause some back-buzzes, which might require raising or lowering the nut height. This is the only penalty that I can see for using less neck relief.