Fretless: action too low or bumpy neck?

[Paolo85]

Hi all, I have a question:

I have Cort B4 fretless, around 10-year-old, with 0.24mm relief, 0.35mm height at the nut and 2mm height at the 12th "fret" (without fretting in first position).
I get a big buzz at the 7th "fret", especially on the A string. This buzz diminishes if I increase relief so it is probably not buzzing at the bottom of the neck. Pushing string height to 2.5mm would not solve the problem for the A. And truth is I'd like a low action and the rest of the fretboard sounds just fine to me.
Do you think the problem is that the action is very low, and I am bound to have some issues especially at the 7th fret unless I get a bass with a perfect ebony fingerboard or something? Or does it look like there is an obvious lump and a luthier can sort it out?

[Andyjr1515]

2mm is a bit low, but not ridiculously so.  Have you tried a 1/4 to 1/2 turn of the saddle height screws on that string?  If so, does the buzz go away?  If it does, then maybe the action is a touch low for your set-up.**I've just re-read your post and see that you've already covered that**  If it still buzzes, then there may be high spot.

 

Finding (or not) lumps and bumps in specific positions on fretless fingerboards is a bit more tricky than on a fretted but the principle is the same.  You use a 'rocker'.  The principle is straightforward.  On a fretted bass, you hold a straight-edge across three frets at a time and see if it rocks when you put vertical pressure alternating either side of the straight edge.  If it rocks, then the middle fret of the three is high.  If it doesn't, it isn't.  And you basically go up the whole fretboard, at each string position, 3 frets at a time to the end.  The further up the board you go, the closer are the three frets and so you have to use a shorter and shorter straight edge. 

 

The principle is the same for a fretless.

 

So, you need a short straight edge, equivalent to covering three fret positions.  For checking at the 7th, the long side of a credit card would be OK:

 

- Pop the bass on the floor or on a worktop and pop some books under the neck so that it won't tip or rock if you apply gentle pressure to the headstock.

- With fingers of each hand holding either side of the credit card, and with the middle of the card over the 7th fret position, hold the card against the A string with the bottom edge on the fretboard (so one end of the card is near the 6th fret position and the other end is near the 8th)

- press vertically down gently on either side of the card and see if it rocks slightly

- If it does, then yes, you have a localised high spot at the 7th

 

Sometimes - particularly with a fretless - the lump is slightly longer and so you could try the same thing with a slightly longer straight edge (6" rule is ideal)   

Edited March 26, 2022 by Andyjr1515

[Paolo85]

Many thanks! I have tried a credit card as well as a rectangular metal ruler (5cm and 9cm/3.5" sides). No bump that I am able to detect. I'll try to find a straight 6" object

Would it be possible that the relief hides a bump? So maybe in that position more than a bump there is lack of curvature?

I have pushed relief up to 0.3mm and string height at 2.5mm. The buzz, while still there, becomes acceptable once amplified. Still I'd love a very low action and I am interested, even just for personal knowledge/future purchases, in understanding how low action can go on a very good neck.

I understand this depend on personal taste on buzz, but the situation I am/was in is that one single note on the fretboard sounds extremely different from all others nearby so I imagine one could "objectively" say that's not great

[Dad3353]

Could it be the frequency of the note itself causing this, with a 'resonance' provoking excess string excursion..? Easily tested, perhaps, by tuning down the whole bass a tone, and seeing if the 'buzz' occurs at the same spot..? Just a thought. 

[Andyjr1515]

3 hours ago, Paolo85 said:

Would it be possible that the relief hides a bump? So maybe in that position more than a bump there is lack of curvature?

 That is possible.  The ideal relief is actually almost none!  When you hold down at the 1st and the 16th, the mid point should have 'just perceptible movement' when you tap it.  If it is hard against the fretboard on either the top string or bottom string, then the trussrod needs slackening off, but as long as there is air underneath both strings, that is enough relief.  And yes - if you are trying to spot a high point, the fretboard should be ideally flat to start with.  But, with you trying the action on that string so much higher and still getting the buzz...and only on that string, is a bit odd and I would have said, if it was caused by a high spot, that would be high enough to be able to pick up even if there was some relief there.  

 

  @Dad3353 's suggestion is a good one.  If raising the action significantly above the other strings (especially the E) doesn't stop the buzz, it points to something else.  Experimenting with the tuning might give a clue.  Tune up a tone too and see if it makes any difference.  It might also be a duff string with more 'slop' than the others.

[Paolo85]

18 hours ago, Dad3353 said:

Could it be the frequency of the note itself causing this, with a 'resonance' provoking excess string excursion..? Easily tested, perhaps, by tuning down the whole bass a tone, and seeing if the 'buzz' occurs at the same spot..? Just a thought. 

 

Interesting! I have tried that, as well as tuning up, it seems the buzz remains on the 7th fret in this case!

 

16 hours ago, Andyjr1515 said:

 That is possible.  The ideal relief is actually almost none!  When you hold down at the 1st and the 16th, the mid point should have 'just perceptible movement' when you tap it.  If it is hard against the fretboard on either the top string or bottom string, then the trussrod needs slackening off, but as long as there is air underneath both strings, that is enough relief.  And yes - if you are trying to spot a high point, the fretboard should be ideally flat to start with. 

I see, maybe I'll bring it in before I flatten the neck, just to avoid playing wit the truss rod too many times possibly without getting anything out of it

 

16 hours ago, Andyjr1515 said:

  It might also be a duff string with more 'slop' than the others.

That could be the case - I am using TI flats so they are already sloppy to start with. Interesting it happens at as specific point in the fretboard though

[Andyjr1515]

29 minutes ago, Paolo85 said:

I see, maybe I'll bring it in before I flatten the neck, just to avoid playing wit the truss rod too many times possibly without getting anything out of it

I agree.  Truss rods need to be handled with care.

 

One more thing you could try is the D string in the A string position.   You would want to use the normal D tuner, but have the saddle to nut in the A position.  The slight kink at the nut shouldn't be any more strain on the string than the normal break angle of the string over the nut in its normal position.

 

 

Then tune it up to D.  If it buzzes in the same place, then yes - there is an issue with the fretboard.  If it doesn't, it's more likely to be the string.

 

 

 

[Paolo85]

Done it with a D from another set of fairly new strings I had recently removed from another bass. It still buzzes. Definitely less I must say, but I believe this is because that D is higher tension than my TI's A (in fact, relief went from around 0.3mm to around 0.33-34mm with the new string on).

On one hand, it seems if I was playing with higher tension strings maybe the problem would be negligible, on the other hand it seems there's something clearly happening at the 7th fret. And I want to play with TI's anyway! It's time to bring it to a professional!

many thanks for your help!

[Andyjr1515]

I agree -  definitely sounds like it needs looking at.  These things are usually relatively easily fixable.  Let us know how you get on

 

Edited March 27, 2022 by Andyjr1515

[Paolo85]

Right, so I brought it to the Gallery. They said there was no visible bump, that level of difference in sound with the other frets is fairly common, but dressing the fretboard could help.

I guess I'll leave it as it is for now and see if it continues to bug me😁