Guitar Neck Relief
To Achieve the Lowest Action on a Guitar
The Neck Relief must be set to zero
Its Cinema Seating Seating... Stupid!
Kevin Aylward B.Sc.
The Myth
Pretty much all guitar luthiers, guitar manufactures, guitar players, as exampled by the numerous YouTube “instructional” videos claim that some neck (bow) relief is required to minimize fret buzzing and achieve low action. They do this, despite, having something like 1.6 mm high E action at the 12th fret, and 2 mm low E action. Fundamentally, these claims are made without actually experimentally determining what neck relief actually achieves the lowest action. If the claimers actually did the tests, it would be clear that, providing that the frets are correctly leveled, the lowest action is achieved with a perfectly straight neck.
I currently have 4 guitars that I have set up with around 0.75 mm action for both high and low E strings, with no fret buzz, achieved by having all the frets uniformly breathed on by the strings when fingered at the 1st and last fret of the fingerboard.
The simplest way to understand why this is so, is to understand why cinema seating goes downhill, and at no time does the seating go back uphill. This is to achieve a clear line of sight for all viewers over the heads of others. Indeed, the ultimate lowest action would be to have the frets having a tapered profile like cinema seating.
The following explains the details:
Typical neck with neck relief showing an approximate triangle is formed from the neck ends to a mid fret position
Simplified neck model that represents the real profile of a guitar with relief
This simplified diagram of the actual neck profile, shows why, if the goal is to achieve the lowest possible action on a guitar, that there should be, essentially, zero relief, in the guitar neck. i.e. there showed be no bow, such that the neck is, essentially, perfectly straight. This is in contradiction to main stream views.
The diagram shows the string clearance from its next fret that would cause a buzz. Whilst it can be seen that the clearance is greater for nut end frets in the “with relief” case, this does not matter if the frets have been leveled correctly. If the clearance at the nut end for the “zero relief” case is set the same as the clearance at the worst case “with relief” case (bow center), then the overall bridge action can be set lower.
It is somewhat stunning that the vast majority of those involved in guitar
subject matters have failed to understand the basic geometry and physics of
the situation. My guess is that there has been a failure to understand that,
although it notionally looks as if there is greater fret clearance closer to
the nut because the action is higher there, the fret clearance after the
maximum bow point is decreased
The link below shows detailed actual measurements of action and neck relief independently proving the validity of the above analysis.
http://www.bryankimsey.com/setup/neck_relief_1.htm
There also are a handful of sites that also address this myth of neck relief,
such as here:
https://dogwoodguitars.com/exploring-common-guitar-myths/ - Myth Number Three: The neck should have significant relief if it is set up correctly