Intonation issue ~ string gauge related, or what else ¿?¿

ChrisMusic

I would really appreciate a little help here...

I have a Dreadnought which is more or less OK on the 1st string, out a little on the 2nd, more or less OK on the third, but wildly out on the 5th and even more on the 6th (all going sharp) at the 12th.

Could this be a string gauge issue ?

The 6th string is also going "dead-ish" or "lacking" and sounding a "bit weird", for want of better words to describe it, progressively from about the 7th fret up.

It arrived with new (I think) strings, but I have no idea what gauge.  I certainly don't want to fit heavy ones and risk damaging the top.  Neck is straight, tiny relief, minuscule belly-up on the top, guitar is about 15 years old I think.

It is actually a good UK made guitar, so I don't think that the bridge would have been fitted in the wrong place, which was my first thought.  The saddle is a single non compensated bar, fitted with what looks like the correct angles.

It is fitted with what I assume is an under saddle piezo, which doesn't seem to work too well with my Sonic Research ST200 tuner, another thing I would like to solve if possible.  That is my only tuner btw.

Whilst I am happy working on electrics, I am totally out of my depth with acoustics, so any help guidance or advice would be much appreciated,

cheers,
Chris

Lewy

What's the action at 12th fret?

I think a good starting point to the troubleshooting would be to fit a set of fresh strings so at least you can be certain of what's on there and go from there.

AliGorie

assuming u have a ‘good’ action at the twelfth fret - do u know how to check intonation ?
hit a harmonic (12th fret) then play the note (fingered) - do this on all strings individually.
e.g. If a note - say 6th string (E) is flat on the finger note compared to the harmonic the compensation is to much on the saddle (the point where the string ‘leaves’ the saddle is to far south and needs brought forward (towards the sound hole and vice versa.
If ya don’t know what all this means do some research to find a ’tech’ who’ll do a decent job.
As u suggest - all this is only relevant for the gauge of string that's on the guitar, but u should be able to get a reasonably intoned guitar with a set of 12’s.
Oh - I don’t trust ‘tuners’ - they tune to math - not music.
Pitch fork for reference note and tune with harmonics = musical tuning.

ChrisMusic

Cheers @Lewy ;

Action is what I would call medium, at the 12th fret is about 2mm0 1st string and maybe 2mm75 on 6th.

It is over 30 years since I last bought acoustic strings, and in a small provincial town, that was basically down to Ernie Ball Phosphor Bonze or playing "air guitar" IIRC.  And then they used to come off, get boiled up, and restrung, eat-sleep-rave-repeat until they broke !

So I really have no idea what to choose now, and there isn't even a shop to go into around here  
I don't do internet shopping either, so I guess that may have to change...

I was hoping that was a decision (and another thread) for another day, but it does make sense, so again any advise isappreciated.

Jalapeno

Saddle askew (or back-to-front if removeable type), would be my first thought if action/relief is fine, and it intonates properly (12th fret harmonic same as 12th fret fretted note).

Jalapeno

Show us a pic of the nut & bridge/saddle if possible .....

Lewy

I'd put a set of D'addario EJ16s  (these are light gauge) on. Just about any online guitar retailer sells them. I always use stringsdirect.co.uk but you might want to shop around as their p&p is a bit steep for a single set. 

One question - when you say the intonation is out ... are you able to use your tuner to see how much by? It may be that actually it's within what would be considered normal for an acoustic with that action and a non-compensated saddle.

ICBM

What make of guitar? Are there any photos online of the same model, or do you have any of it?

It's worth checking the nut height and neck relief, although from the action measurements you've given it doesn't sound like there is a major problem there.

Try a new set of strings first. There is no acoustic guitar I know of that's designed for steel strings that won't take 12s so you should be safe enough with those, but if you're unsure then try 11s.

But it sounds like there could be a problem with the bridge position since even with all those things not adjusted well, it's very rare to find the intonation that badly out.

Some acoustic guitars do shrink along their length as they settle down under the string tension, which brings the bridge forward and will cause this. It's not that common because the design of the top bracing is enough to resist it to a large extent, but it can happen especially if the wood wasn't completely stable when the guitar was made. Hopefully it isn't this, because if so then the only fix is to move the bridge - either by filling the slot and cutting a new one further back, or increasing the width (towards the back only) and using a wider compensated saddle.

For what it's worth I don't usually use a tuner to check and set intonation either - I use the strings as a reference for each other, because that's how you actually hear a guitar when you're playing it - they can be quite useful for solving problems like this because they give you a more accurate indication of how far out it is, rather than just "not much" or "a lot", which can be harder to judge by ear.

ChrisMusic

Thanks @AliGorie  ~ yes that's how I am checking intonation.

When I played acoustic before, a long time ago, I always used a pitch fork, harmonics and adjust by ear to taste after.

I still do that now with electric, as long as the A is in, and reach for the tuner either to confirm on those infernal days when I just can't get it right, or when I have to retune to concert pitch, or to confirm intonation.

It seems further out than I would expect for a string gauge issue, but then I haven't used anything heavier than 10s on electric, so returning to acoustic, and ~ loving it ~ BTW, is almost a new experience !

ChrisMusic

The ST200 is a "strobe" tuner, and has that lovely rotating wheel "light show", great to watch in the dark, and scarily accurate, but doesn't give ± cents reading, which might be useful right now.

Unfortunately I don't have any way of posting pics right now, but the bridge looks about right, angled as I would expect, and the perpendicular is angled towards the sound hole too, nice touch there.

The nut to 12th is slightly longer than 12th to bridge, according to my missus' ropey old tape measure.
**edit: I have now checked with an engineers rule and it appears to be exactly the same, i.e. no compensation at all !

Nut is original, and height is fine, but I have a suspicion that it may be part of the problem.  Can the fulcrum point change, or move back a little with time and use?

Subject to how this pans out, I may try a compensated saddle, or recut the pitch of this one slightly.

I would love to get to the bottom of this within the forum, and maybe do any remedial work myself, if possible.

I am sure the wood was well sourced and adequate for the job, the top sounds great with a scratchy fingernail test.  I am sure the bridge would have been located perfectly too when it was made.  I didn't know that shrink could be a potential problem, so thanks for continuing my education @ICBM, all knowledge is a valuable gift

I have also eMailed the maker, and am still waiting to hear back from him.

ChrisMusic

So would I be correct in assuming that this is unlikely to be a string gauge issue ?

AliGorie

heres the techie stuff on compensation -
http://liutaiomottola.com/formulae/compensation.htm

ChrisMusic

Thanks for the link to an excellent resource @AliGorie , a little light bedtime reading, methinks  

Winny_Pooh

Check the relief. If there is too much the nut will be physically closer to the bridge and this makes a bigger difference than you would think.

ICBM

Winny_Pooh said:

Check the relief. If there is too much the nut will be physically closer to the bridge and this makes a bigger difference than you would think.

I don't think that can possibly make enough difference to be detectable as an intonation problem.

I tried to work out the difference by geometry but I'm too out of practice so I gave it to my teenage daughter to work out . I did a rough approximation assuming that the neck and strings are two sides of a triangle, which they aren't quite because the neck is curved - and found that with a relief of 2.5mm (which is huge) then the nut will be two hundredths of a millimetre closer to the bridge.

I'll see if she can get the right answer assuming it's a curve...

Jalapeno

ICBM said:

Winny_Pooh said:

Check the relief. If there is too much the nut will be physically closer to the bridge and this makes a bigger difference than you would think.

I don't think that can possibly make enough difference to be detectable as an intonation problem.

I tried to work out the difference by geometry but I'm too out of practice so I gave it to my teenage daughter to work out . I did a rough approximation assuming that the neck and strings are two sides of a triangle, which they aren't quite because the neck is curved - and found that with a relief of 2.5mm (which is huge) then the nut will be two hundredths of a millimetre closer to the bridge.

I'll see if she can get the right answer assuming it's a curve...

He said nut to 12th fret is longer, not shorter.  Bridge position is wonky, not neck relief, or worse still the scale calculation and fretting is all off .....

What are the distances nut-to12th, and 12th-to-bridge ?

AliGorie

not suggesting - but.
there was a guy on a big US forum questioning the QC of a famous Chinese brand, re scale length - 4 pages of advice on what SL was and how to measure it accurately. He started to get stroppy and I mentioned the (center of the fret crown) - he hadn’t a clue - crazy figures he was coming up with.
Eventually it turned out he thought the ‘12th fret’ was the space between  the eleventh and twelfth fret  ‘Yard Stick’ was correct and he was measuring it correctly - just not measuring the right thing.
If u got a ’standard’ dread - should be a 645 mm SL from the edge of the nut to the (crown’ of the 12 th fret) should be 322.5mm and from the crown (center)  of the 12th fret to the saddle (1st E string) should be 322 + a couple or so mm for compensation - note as the strings get ‘thicker’ the compensation gets larger - depending on the gauge of the strings - also note that ‘compensation’ is for the gauge of the ‘core’ wire (mainly).- Look at an electric guitar saddle - the unwound ‘G’ string gets more compensation than the ‘D’ - this is because the ‘unwound G’ is ALL ‘core wire’, the wound ‘D’s’ core wire is thinner than the ‘G’.. Conversely on an acoustic the WOUND ‘G’s’ core wire is thinner than the unwound ’B’ so gets less - is not as far back.

hope I’ve got all this right.

ChrisMusic

Yes, I do know the difference , but not everyone accessing this thread might, so that is a very valid (and somewhat amusing) point to raise here IMO, thanks.

After giving up on my other half's tailor's tape, which apart from being found in the wreckage of the Titanic (probably), looks like it has provided a mini feast for our resident house mouse at some point, so it is a bit too stretchy !   It also only measures to 1/8th of an inch delineations, so moving on...

Old steel engineers foot rule, dodgy eyesight*, and a bit of iteration later...

Nut face (crown?) to 12th crown 321mm
1st string bridge crown to 12th crown 318mm
6th string bridge crown to 12th crown 321mm

so approx 3mm straight line compensation from 1st to 6th strings

To reiterate: 1st string is only very slightly sharp at the 12th, 2nd is sharp, 3rd is almost spot on, 4th is slightly sharp, 5th is quite a bit sharp and 6th is way sharp, unplayably so.

And oddly ?  nut face to crown of 5th fret is ≈ 161.4mm and 5th crown to 12th crown is 159.5mm approx

Measurements are as near as I can tell*

Winny_Pooh

ICBM said:

Winny_Pooh said:

Check the relief. If there is too much the nut will be physically closer to the bridge and this makes a bigger difference than you would think.

I don't think that can possibly make enough difference to be detectable as an intonation problem.

I tried to work out the difference by geometry but I'm too out of practice so I gave it to my teenage daughter to work out . I did a rough approximation assuming that the neck and strings are two sides of a triangle, which they aren't quite because the neck is curved - and found that with a relief of 2.5mm (which is huge) then the nut will be two hundredths of a millimetre closer to the bridge.

I'll see if she can get the right answer assuming it's a curve...

I've seen it make a difference on my guitars, but then I am more fussy with intonation that most & use the feiten offsets on electrics. 

If the fretted notes are sharp then the saddle needs to go back & I have seen reducing the relief help as the increased lower action that results also contributes to a change in intonation. 

Mind you, per the latest post If the 6th string is too sharp at the 12th then the saddle needs to be recut. (shaving the nut end of the fretboard could be good too.)

ICBM

Winny_Pooh said:

I have seen reducing the relief help as the increased lower action that results also contributes to a change in intonation.

Yes, it's this which is why too much relief causes intonation problems, not the change in scale length/nut position - it's simply because if there's too much relief, you're pulling the strings down further to fret them and hence bending them sharp.

My daughter still hasn't worked out the true change in scale length (maths is not her favourite subject, to be fair…), but it's got to be really close to the approximation with straight lines.

earwighoney

ChrisMusic said:

It arrived with new (I think) strings, but I have no idea what gauge.  I certainly don't want to fit heavy ones and risk damaging the top.  Neck is straight, tiny relief, minuscule belly-up on the top, guitar is about 15 years old I think.

What is the scale length of the guitar?  I'd start off with a set of 12-53's to begin with and see how the intonation goes from there.  

Another to address which hasn't been mentioned here is if the guitar has acclimatised to your conditions.  IMO, a slight change in humidity, whether the guitar is too dry or too wet can significant impacts on intonation - more so with a lighter built guitar, then issues like a nitro, oil, shellac finish would impact this issue. 

Then you've saddle and the nut, and if they are looking worn out then an oversized/overhang saddle and a compensating nut could remedy the situation.  Chris Alsop makes a few for not a huge amount all things considered, pleased with the nut I bought from him.