Intonation, anyone?

Okay, am I expecting something from a tenor ukulele that just ain't gonna happen? What I've tried is to compare each string from nut to 12th fret and shape the saddle according to what I find. The C required more length that the others and is the only one that I could get close. Everything else didn't improve the more I filed the saddle. And comparing up the fret board on each string, they seem better lower (6-7th fret or so).

I am using an Android app "Airyware" to check, by the way.

Without knowing the numbers you are trying to achieve it is difficult to answer your question directly. The math behind the fret calculations is precise, but there are a myriad of factors that effect the outcome in the real world. String variations, fretting technique and even temperature effect the actual note. A few GAL conventions ago two guys from Stew-Mac gave a presentation on achieving near perfect intonation on a guitar. The details have faded from my memory, but I do remember that it was a tedious process involving compensating the nut as well as the saddle, while keeping all the other parameters, i.e. the strings, identical. The one takeaway for me was, after I cut my fret slots, I remove about .5 mm from the top of my fretboard which seems to improve the intonation of the lower frets.

Bradford

If the fretted note sounds flat bend it in.. or use vibrato like violinists do.

BuzzBD said:

Without knowing the numbers you are trying to achieve it is difficult to answer your question directly. The math behind the fret calculations is precise, but there are a myriad of factors that effect the outcome in the real world. String variations, fretting technique and even temperature effect the actual note. A few GAL conventions ago two guys from Stew-Mac gave a presentation on achieving near perfect intonation on a guitar. The details have faded from my memory, but I do remember that it was a tedious process involving compensating the nut as well as the saddle, while keeping all the other parameters, i.e. the strings, identical. The one takeaway for me was, after I cut my fret slots, I remove about .5 mm from the top of my fretboard which seems to improve the intonation of the lower frets.

Bradford

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Thanks, Bradford! Numbers-wise I'm seeing about 5 to 8 cents difference. Enough to hear to be sure.
Do I understand you correctly as saying that there are better brands of strings for intonation than others?

Timbuck said:

If the fretted note sounds flat bend it in.. or use vibrato like violinists do.

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Ken, I'm guessing that the answer to my question is yes, I am asking more of the ukulele than it can deliver? That I cannot expect high accuracy.

It is true that some brands of strings will have better intonation on a certain ukulele, but overall it is not that simple. It also happens that changing strings from the same brand can also have an effect, one way or another. The fact is, those nice numbers in thousands on the string diameters are nominal. Strings can vary in diameter along their length, sometimes by quite a bit and especially when they are placed under tension.

The other issue that Ken alluded to is that it is difficult not to bend a string one way or another when fretting it. There is a reason why great players sound really good and that is because of their fretting precision. I have no idea what your skill level is and certainly repetitive trials will identify the trends.

Bradford

ChuckBarnett said:

The C required more length that the others and is the only one that I could get close. Everything else didn't improve the more I filed the saddle. And comparing up the fret board on each string, they seem better lower (6-7th fret or so).

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Your explanation of what you've done is very brief so I'm guessing here, but it reads as if you already had a little too much compensation on all strings except the C. So filing back the saddle for those strings would make matters worse!

The process of compensation is as follows:

1. As a starting point, the saddle need to be at a position so that none of the strings produces a note at the 12th which is flat compared to the open string. If any are flat, the saddle needs to move forwards (towards the headstock) because the saddle slot has been cut too far back. With luck, a new saddle blank with its peak shaped further forwards will achieve this, otherwise it's a more complex fix.

2. Then for each string individually, gradually file back the peak of the saddle until the open and 12th notes are exactly an octave apart, or near enough so you can't hear the difference. This produces a saddle which has four differently placed peak sections, one for each string.

3. Finally, smooth over the peaks - this will move them all back a fraction, so it's probably best to start the smoothing when the 12th still rings a fraction sharp.

Intonation will alway be closer on the lower frets (if it's not right for all of them) because fretting at the lower frets stretches (sharpens) the string less than at the 12th - the string is closer to the top of the fret lower down.

A few other points to bear in mind:

1. Finger pressure makes a huge difference. I just measured 20 cents between fretting so the note just rings clearly and pressing the string rights down onto the fretboard.

2. High action at the 12th (I'd say over 3mm) means that fretting stretches the string so much that you may never get decent intonation.

3. Setting the intonation only works for those particular strings - a different brand/type will be more or less stretchy, and so will require a different amount of compensation.

I made a few tenor ukes a few years ago..On the low G string I made the compensation at 3mm and got good results .. I got the compensation figures from the David Hurd "Left brained luthiery" web site This was the bridge with the movable G saddle.

And this is a sound sample video of that low G with a Nylon wound Classical guitar D string fitted.
https://www.youtube.com/watch?v=lhCwhPKEQcE

I just made a fretless tenor uke- it technically has perfect intonation over the whole fretboard!

Intonate for one set of strings, then change those strings, the intonation will likely be different.

I have often found that if a certain set of strings are intonating sharp, and all meaningful setup adjustments have been done to remedy the problem but intonation is still amiss, another good solution that has worked for me is to use strings with greater tension, which typically are strings with higher gauges.

Worth strings has ~15 different gauges each in both clear and brown series.

From one set to the next, there is a difference in tension of about 5 lbs in total for each set, and should be within spec for the given scale length where they are to be installed.

I agree with what others have said above about adjusting for each specific set of strings - many years ago before I sold and gave away all of my traditional ukes and decided to stick with just a concert Flea from Magic Fluke Company, I had different nuts and saddles that I could easily swap out, and each set was specifically adjusted for either flurocarbon strings of a specific gauge or nylon strings of a specific gauge.

This allowed me to get intonation within about 3 cents (sharp) across all four strings, and all the way up to the 15th fret, and yes on soprano, concert and tenor.

From my own personal experience, IMHO anyone that is saying that good intonation is not possible on ukulele is either woefully misinformed or lacks sufficient experience with doing setups while also trying out lots of different gauges and materials of strings for ukulele.

So to the OP, you might have to spend for 5-10 different sets of strings in different gauges and materials (which will all have slightly different tension) and by process of elimination, figure out which strings work on your instrument in front of you.

Joe King said:

This allowed me to get intonation within about 3 cents (sharp) across all four strings, and all the way up to the 15th fret, and yes on soprano, concert and tenor.

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I have a D'Addario indicated by horizontal bars, and a Kala needle swing from -50 to+50. How do these translate to cents?

If I understand what you are aking. Those numbers are cents. Thus -50 to +50 would be 100 cents or one simitone.

You need to start from the start and measure the instrument for accurate placement of the saddle and nut to begin with.

Just assuming that any and every instrument was accurately constructed in the first place is a fundamental mistake.
Actual scale length should be inside nut to centre of 12th fret x 2 + saddle compensation. The nut needs to as carefully and accurately positions as the saddle. How accurate is the fretting?

Start by taking some measurements.

Kekani said:

I would say yes, and no to your query. Depends on if you expect perfect on every not - set fret instruments are a series of compromises, usually.

More details specific to your build please:
What strings?
Tuning? High or low g (assuming a tenor)?
Scale length? Specifically, nut to 12th, nut to front of saddle, nut to rear of saddle would help.
Who cut your fretboard?

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Thanks, Kekani, for jumping in!

These are Aquila Nylgut strings. Low G

I cut the fret slots using a tenor ukulele LMI template and my table saw.

Here are a couple pics that give the measurements you asked about.




The saddle is set in at 6 -7 degrees back-tilt (Thanks, Beau H, for the idea.)

Regarding finger pressure and bending, etc., I tried my best to go light. But given that this is my first try at intonation and set-up of anything, well...

Perhaps I should try a fresh set of strings? These have been slacked and tightened several times in their 4 weeks of life on this instrument.

Judging by the photo's and assuming a 17" nominal scale length then I would be expecting that the intonation is a little Flat. There is compensation on the nut and plenty on the saddle. Which way is the intonation going and by how much.

If the intonation is going sharp then I would be leaning towards the strings being the culprit.

EDIT: I expect Aquila Nylgut strings to be white in colour. Are they Aquila Lava strings instead?

I think your saddle peak is too far back. All your 12th notes are flat.

Your ruler shows 8.5 inches at the 12th, giving a nominal 17 inch scale. Your saddle peak is set at 17.25, or a fraction less. That's nearly 1/4 inch of compensation, or around 6 mm (the units I think in for this job).

For a tenor I'd expect compensation to be something like: A - 1mm, E 1.5-2mm, C - 2.5mm, G 1mm.

You could check this out by double-sided taping a scrap of wood to the front of the saddle and filing it back, as I described earlier, to find out where your saddle peak should be - I expect it should be at least 1/8 (3mm) closer to the nut, possible a fraction more.

Once you've worked this out the question is how to fix it. Simplest might be to make an oddly-shaped saddle which matches your existing saddle + wood extra. It will look odd, but only builders will notice!

I suspect the "proper" answer is to fill the slot and recut it in the right place, but I don't think you have enough space for a tilted saddle further forward. A straight saddle might just be possible.