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Dead spot on a fretless... What to do ?


Torben Hedstrøm
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Hi...

I own a fretless Warwick Thumb BO, and I am completely in liove with everything about it... Except... After adjusting relief & string height I found that I have a 'dead spot' juuuuust above what would have been the 6'th fret. I could probably just raise the action and get rid of it, but I really like my action nice and low. Guess I need a luthier to have a looke at it ?!.

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Correct me if I'm wrong, but can't adjusting the truss rod help to iron out/shift dead spots elsewhere on the neck?
Perhaps just tighten it a TINY amount (not enough to alter the relief) and see what happens.
Only about 1/32 of a turn against the tension of the strings. It might work. If it doesn't, just reset the rod and try something else?

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That area, usually around C-D on the G string, is the common ground for this on some basses. There's a whole science devoted to this symptom on the net but , as stated about, sometimes a tweak of the rod can alleviate the dead-spot in the first instance. I've got it one a Fender CS fretless Jazz; had it since I got it and it's taken ten years or so for it to lessen, possibly due to the neck/body losing more moisture. It's not as bad as it used to be, but you can still hear and feel it!

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[quote name='Torben Hedstrøm' timestamp='1350488529' post='1839599']
I could probably just raise the action and get rid of it, but I really like my action nice and low.
[/quote]

Would be worth trying this. If the dead spot does disappear when you raise the action then it's most likely just a slight imperfection with the flatness of the fingerboard (which is relatively easy luthier fix) rather than a dead spot due to structural resonance in the neck (which isn't!).

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[quote name='mart' timestamp='1350575997' post='1840795']
If it's the resonant frequency, then it'd be the same wherever you played that same note, right?
[/quote]

No, not necessarily. Different resonant frequencies occur in different places along the neck. A dead spot is where the frequency of the fretted note coincides with the antinode of the resonant frequency of the neck at that exact point (or very near). Fretting a note of the same frequency somewhere else on the neck (on a different string) may not result in a dead spot as the resonant frequency of the neck at that point may be different or the position of that fret may not be so close to the antinode.

This article explains it much better than I can - [url="http://www.acoustics.org/press/137th/fleischer.html"]http://www.acoustics.../fleischer.html[/url]

Edited by ikay
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[quote name='mart' timestamp='1350575997' post='1840795']
If it's the resonant frequency, then it'd be the same wherever you played that same note, right?
[/quote]

It is also further complicated by requiring sufficient amplitude to cause the cancellation. The effect is likely to be less at higher frequency notes - less energy transmission. Not a simple situation and no simple magic bullet cure.

If the previous suggestions do not help, in no particular order;

Mass (brass?) plate screwed on back of neck (fatfinger as suggested before). Neoprene gasket in neck pocket ( there will be outcries about poor neck / body contact). Check neck pocket level / flatness. Thin aluminium/ steel plate in neck pocket. Metal plate under bridge. 'Big' metal block/insert under bridge. Metal strip under machine heads. Change machine heads. Rout body under pickguard , remove wood. None of these may work however :(

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[quote name='ikay' timestamp='1350593782' post='1841135']No, not necessarily. Different resonant frequencies occur in different places along the neck. A dead spot is where the frequency of the fretted note coincides with the antinode of the resonant frequency of the neck at that exact point (or very near). Fretting a note of the same frequency somewhere else on the neck (on a different string) may not result in a dead spot as the resonant frequency of the neck at that point may be different.

This article explains it much better than I can - [url="http://www.acoustics.org/press/137th/fleischer.html"]http://www.acoustics.../fleischer.html[/url]
[/quote]
Interesting article - thanks for finding that. So yes, it really isn't as simple as I had thought.

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  • 2 weeks later...

Hi...

Thanks for the concern... Still stalling on the luthoier thing, I'm afraid. Not because I won't pay up, but I feel REALLY reluctant handing over a precious instrument for sanding to just anyone. And case is, I have no references on any Danish luthiers yet. The buzzing is not bad enough to make the bass unplayable, so for now I just avoid that particular part of the neck ;)

:)

Torben

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  • 3 months later...

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