Does the maths add up?

Frankieabbot · December 2015

Taking 2mm off the bottom of an acoustic saddle will :- 1) Lower the string height at fret 12 by 1mm. 2) Lower the string height at fret one by approx 0.05mm.

mart · December 2015

Yes about the 12th, but at the 1st fret it'll lower it by just over 0.11mm, in theory at least.

Frankieabbot · December 2015

mart said:

Yes about the 12th, but at the 1st fret it'll lower it by just over 0.11mm, in theory at least.

Thanks bud.

mart · December 2015

You're welcome. The 1st fret is approximately one eighteenth of the way from the nut to the bridge, so the change in height there will be approximately one eighteenth of the change at the bridge. (Assuming you leave the nut unchanged).

richardhomer · December 2015

Just before you get stuck in - don't forget that action and relief are inextricably linked. Make sure the neck is properly adjusted before doing anything.

Secondly, the correct way of checking nut height is to fret each string at the third fret - it should be possible to lightly tap each string on to the first fret (using your other hand). There should be a gap between the bottom of the string and top of the first fret - but it should be very slight (a couple of thousands of an inch or so). This method takes saddle height out of the equation when assessing the nut.

Finally, the amount of belly in the top of an acoustic varies a lot with humidity. In dry conditions, they flatten out - which will drop the bridge lower. In more humid conditions, they bow more, which lifts the bridge.

You need to consider all of these issues before cutting the saddle down. Often the reason an acoustic's action is too high is due to a combination of these factors - and cutting a saddle too low can compromise tone due to the lack of break-angle.

stickyfiddle · December 2015

richardhomer said:

Just before you get stuck in - don't forget that action and relief are inextricably linked. Make sure the neck is properly adjusted before doing anything.

Secondly, the correct way of checking nut height is to fret each string at the third fret - it should be possible to lightly tap each string on to the first fret (using your other hand). There should be a gap between the bottom of the string and top of the first fret - but it should be very slight (a couple of thousands of an inch or so). This method takes saddle height out of the equation when assessing the nut.

Finally, the amount of belly in the top of an acoustic varies a lot with humidity. In dry conditions, they flatten out - which will drop the bridge lower. In more humid conditions, they bow more, which lifts the bridge.

You need to consider all of these issues before cutting the saddle down. Often the reason an acoustic's action is too high is due to a combination of these factors - and cutting a saddle too low can compromise tone due to the lack of break-angle.

This!! The numbers are correct but only if the neck is straight!!

mart · December 2015

stickyfiddle said:
This!! The numbers are correct but only if the neck is straight!!

Yes and no.

I agree that one should not wade in and adjust the saddle without taking into account the other factors that @richardhomer mentioned.

However, the numbers quoted are correct regardless of the shape of the neck, at least to quite a high degree of accuracy. This is because the precise distances being discussed are determined by the shape of the string which, under tension, is very nearly a perfect straight line. If you move one end of this straight line by 2mm, then each point on that line moves by a proportionate amount. So if you measure with reference to a given datum line (which can be a curve, e.g.., the neck) the measurement will change exactly by that amount.

The only inaccuracy here is that changing the bridge height will very slightly affect the direction in which the strings are pulling, which may very slightly affect the shape the next takes, having a consequent effect on the datum line. But those changes are going to be tiny in comparison.

/pedant mode.

stickyfiddle · December 2015

@mart Yes, completely agree- it's more a case of "make sure the neck is straight before you start so you're sure the saddle is the thing you need to adjust"

mart · December 2015

@stickfiddle Ok, now I get you, and completely agree.

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Does the maths add up?

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