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Old 11-17-2021, 04:51 PM
javierj javierj is offline
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Default Does saddle height affect first 7 frets height?

Hello,

Quick question, when you are doing a setup on an acoustic guitar. Let's say you already have set your ideal neck relief and nut height. Now when you lower the saddle height to set your action at the 12th fret, how much does saddle height affect the height of let's say for example the first 7th to 9th frets? I ask because it seems to me that when you lower the saddle height, it has more effect on string height on the higher frets like for example maybe from the 10th fret to the rest of the frets of the neck. Reason I ask, is because if you feel like you would want mostly the first 7 to 9 frets to be lower in height, maybe lowering the saddle is not going to have much effect on them. It will probably have more effect on 10th to 20th frets. Could you elaborate a little for me on this one, so I can understand this better?

Thanks a lot!
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Old 11-17-2021, 06:14 PM
John Arnold John Arnold is offline
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If you assume a straight neck, then the strings and the fret plane constitute two lines that intersect at the nut. With that in mind, then it is simple geometry to determine how much action change occurs at any point on the fingerboard due to a change in bridge height.
Basically, the action change is proportional to the distance from the nut.
For example, the distance from the nut to the fifth fret is roughly half the distance from the nut to the 12th. That means that the action change at the fifth fret will be half that at the 12th.
Similarly, the action change at the first fret will only be 11% of the change at the 12th.
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Old 11-17-2021, 06:38 PM
javierj javierj is offline
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Thanks a lot for the information, it is very helpful!

So in other words if you wish to lower the string height in the first 7 frets, you are not going to get too far by lowering the saddle. Especially in the first 5 frets. You are more likely to achieve it by lowering the neck relief with the truss rod. Because you will really had to lower the saddle a lot, to try and lower the height in the first 5 frets and then you will end up with a very low saddle and possibly getting fret buzz on the higher frets, like 10, 12th and up...
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Old 11-17-2021, 07:32 PM
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Brent Hutto Brent Hutto is offline
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Quote:
Originally Posted by javierj View Post
Thanks a lot for the information, it is very helpful!

So in other words if you wish to lower the string height in the first 7 frets, you are not going to get too far by lowering the saddle. Especially in the first 5 frets. You are more likely to achieve it by lowering the neck relief with the truss rod. Because you will really had to lower the saddle a lot, to try and lower the height in the first 5 frets and then you will end up with a very low saddle and possibly getting fret buzz on the higher frets, like 10, 12th and up...
No, I don't think that is going to work at all like you're picturing it working.

You seem to be describing either a neck with backward bow (like negative relief) or some frets badly in need of leveling.

The only thing you can accomplish with the truss rod is, once the action is basically where you want it with the neck flat, you can add a small amount of extra "relief" in the middle of the neck (say roughly the 5th to through 10th frets). If you try to lower the action in the "first 5 frets" by cranking on the truss rod you'll damage it way before you make any meaningful change.
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Old 11-17-2021, 09:54 PM
javierj javierj is offline
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Thanks for your reply!

Yeah I am not going to try and lower the action at the first 5 frets by cranking on the truss rod. My neck relief is fine. It is around 0.006 inch and none of the frets are badly in need of leveling, there is no fret buzz any where. I was just trying to understand something, but I think I got it...

Last edited by javierj; 11-17-2021 at 10:18 PM.
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Old 11-17-2021, 09:59 PM
javierj javierj is offline
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Originally Posted by John Arnold View Post
If you assume a straight neck, then the strings and the fret plane constitute two lines that intersect at the nut. With that in mind, then it is simple geometry to determine how much action change occurs at any point on the fingerboard due to a change in bridge height.
Basically, the action change is proportional to the distance from the nut.
For example, the distance from the nut to the fifth fret is roughly half the distance from the nut to the 12th. That means that the action change at the fifth fret will be half that at the 12th.
Similarly, the action change at the first fret will only be 11% of the change at the 12th.
Something else that I always being curious, is how the string height starts to progressively get higher from the first to the last fret of the neck. Like for example in all guitars that I have seen, the string height from the 3rd fret for example, seems to be half of what it is on the 12 fret. So if where are assuming that the neck is straight, how can we explain the difference in string height from the the 3rd fret to the 12th or even 17th fret?

I had read somewhere that the string action of like the first 5 frets could be set by the nut height, does that make any sense?
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Old 11-17-2021, 11:21 PM
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Quote:
Originally Posted by javierj View Post
Something else that I always being curious, is how the string height starts to progressively get higher from the first to the last fret of the neck. Like for example in all guitars that I have seen, the string height from the 3rd fret for example, seems to be half of what it is on the 12 fret. So if where are assuming that the neck is straight, how can we explain the difference in string height from the the 3rd fret to the 12th or even 17th fret?

I had read somewhere that the string action of like the first 5 frets could be set by the nut height, does that make any sense?
It's called an angle. The fretboard is straight but the string is interested in the bridge and nut and the bridge is higher than the nut.
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Last edited by rick-slo; 11-17-2021 at 11:28 PM.
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Old 11-17-2021, 11:27 PM
javierj javierj is offline
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Quote:
Originally Posted by rick-slo View Post
It's called an angle.
Got it!

Thanks
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Old 11-17-2021, 11:58 PM
javierj javierj is offline
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Originally Posted by rick-slo View Post
It's called an angle. The fretboard is straight but the string is interested in the bridge and nut and the bridge is higher than the nut.
So I guess that is why guitars are constructed like that, with the string height higher on the higher frets. Because you need higher string height at the upper frets like from 10th to the last, than the first 7 frets, to be able to to clear the next fret when you depress a fretted note, without getting fret buzz...

Last edited by javierj; 11-18-2021 at 12:06 AM.
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Old 11-18-2021, 12:13 AM
javierj javierj is offline
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Sorry to ask this rather dumb questions, but the really dumbest thing I heard, was on some other forum somebody saying that their guitar was quite higher in string height on the upper frets compared to the lower frets like the first 5 frets. Some people or even several people, told the guy to take the guitar to a tech to correct that, saying that there should not be much diferent in string height in a guitar from let's say the 3rd fret and the 12 fret. Of course there is a diference, I think it could even well be almost double of difference in height. That is why I wanted to talk about this
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Old 11-18-2021, 02:17 AM
John Arnold John Arnold is offline
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So I guess that is why guitars are constructed like that, with the string height higher on the higher frets. Because you need higher string height at the upper frets like from 10th to the last, than the first 7 frets, to be able to to clear the next fret when you depress a fretted note, without getting fret buzz..
.

Look at it logically. The correct nut height is the same as the frets. The strings must get higher as you go up the neck, otherwise, the strings would be laying on the frets. Raise the nut to equalize the action, and the intonation goes bad, plus the guitar becomes unnecessarily harder to play in the first position. Lowering the saddle also equalizes the action, but you know what happens when the action is too low for your playing style.
Your analysis of the requirement of higher action on the more closely-spaced frets does not factor in that as the vibrating string gets shorter, its excursion gets less, reducing the tendency to buzz. And the angle that the string leaves the fret becomes greater. Those factors mean that there is a relief setting where the tendency to buzz is essentially the same all along the neck. This is a very small amount, usually between 0.003" and 0.010" It turns out that this is largely independent of the action setting.

Quote:
in all guitars that I have seen, the string height from the 3rd fret for example, seems to be half of what it is on the 12 fret.
That would be true when the nut is too high, and/or when there is too much relief. Too-high nuts are common on factory setups to avoid buzzing on open strings. This is usually to compensate for some wear of the nut in the slots.
With an adjustable rod, there is no justification for too much relief. It will increase the tendency to buzz above the 6th fret. If the action is too low, raise the saddle instead of loosening the rod.

Last edited by John Arnold; 11-18-2021 at 02:24 AM.
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Old 11-18-2021, 06:00 AM
Robin, Wales Robin, Wales is offline
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There are some excellent responses here regarding guitars.

As an aside, I have seen historic mountain dulcimers where the nut and bridge have been the same height and the strings running parallel to the fretboard. However, the frets on those instruments were placed by ear not to a set formula. So the instruments would play beautifully in tune, BUT only if you used the string gauge and pitch (usually the instruments were quite randomly tuned to a "good" note) that the original builder used. You really wouldn't want a guitar made like that!!!!
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Old 11-24-2021, 05:00 AM
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FWIW, I was taught to set the neck relief first, then the saddle height (to set action) then file nut slots to proper depth. The saddle height will remain in play at all times, as where nut height really only affects open strings and fretting in the first couple positions. Of course, there are widely differing opinions on this.
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Old 11-24-2021, 11:00 AM
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It's a system, they are all connected... everything affects everything... cue mystical music and eerie smoke effects...

Seriously the information given herein is really good stuff. With that said, I could really easily set up a guitar with 1/16" action height (my normal 12th fret action setting) all up and down the fret board, every fret would have 1/16th" string height. It would play like junk, it would buzz with any volume, and it would be really hard to play from the first to around the fifth fret. But you could do it.

One of the artifacts of how the guitar works is that if your nut action is right, your 12th fret action is right, your neck relief is right, the amount of work needed to press down the strings is pretty constant no matter where you are on the neck. You might need to press down .010" at the first fret or .06" at the 12th fret, but it takes a similar amount of pressure. It's neat how that works out.
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