Dead notes and the Truss Rod

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noplanb
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Dead notes and the Truss Rod

Post by noplanb » 12 May 2018, 13:41

I have been researching this and doing some experimenting. This is an overview -Please comment and I'll add new approaches to this collection.
Examples of remedies shown following.

Situation
Dead notes are when something on the bass vibrates sympathetically at that note, and thus subtracts energy from the plucked string, and decays the plucked note quickly, thus making a dead spot.
Causes can be:
1) Loose tuners, string tree
2) Too long a string between nut and tuner
3) Something in the neck itself:
a) woods?
b) Loose/vibrating truss rod

Example forum discussion of vibrating trussrod, but with deadspot implications:
https://www.seymourduncan.com/forum/sho ... at-do-I-do

Most likely cause:- it would appear the majority of bass deadspots may well be due to the trussrod being undamped, due to wood shrinking over time, thus creating less area of rod touching the wood of the channel.
Fixes at manufacture::
1) Rods may have a PVC or similar coating or sleeve
2)Rod is installed with a non-hardening gel at a few spots along its length, eg silicone
3)Rod is installed with a foam strip in the wood channel

Fixes after manufacture

1) Adding mass to the headstock
Effectively changes resonance of the whole neck, including the trussrod. It seems that the head end of the neck is more sensitive than the bridge for (unwanted)string dampening .
https://www.researchgate.net/publicatio ... ass_Guitar
Hypothesis - this spreads the unwanted resonance across more modes of vibration, thus reducing the peak unwanted resonance, and maybe imperceptibly increasing a few other deadspot notes.
a) "Fat Finger" - a screw-clamp on the headstock - reasonably effective but ugly
b) Changing the Tuners for heavier hardware (- not tried yet)
c) Adding a bolt-on plate (brass or steel)to the back of the headstock - quite effective but requires basic metalworking skills

2) Damping the neck
a) Bolt-on neck - 'damp' a screw by loosening it slightly - not a good long-term solution
b) Bolt-on neck - 'damp' screws by adding flexible washers under heads - limited effect (- not tried yet)
c) Bolt-on neck - add thin flexible pad, eg neoprene, evenly under the heel - beware as the neck is now raised 1 or 2 mm, and pups and bridge will have to be adjusted accordingly (- not tried yet)
d) Add dense flexible pad (eg neoprene) to all of rear of headstock - may entail using a removable grade glue to keep it evenly touching the whole headstock surface (- not tried yet)

3) Damping the Trussrod
a) Place O-ring under the trussrod nut - reasonably effective, O-ring squashes but still provides some damping! Use 2 if enough thread available
b) Insert stiffened wire into the truss-rod cavity(!) - Does 2 things, adds mass to the truss-rod assembly thus changing its resonance, and jams the truss rod against the wire against the wood - reasonably effective
c) Inject 'benign' filler into the trussrod cavity - it creates a weak bond between the rod and the wood, it also may cause the wood to swell a little into the cavity, thus assisting damping. This can be water-diluted PVC glue, and is like something called 'Chair-Loc' (used for expanding dowel joints in chairs)
Can be injected via the trussrod opening once the adjusting-nut is removed, or via a removed part of the fingerboard, eg dot or the nut.
PVC -> http://www.lydian.ca/loose-rattling-truss-rod/
Wax -> https://www.premierguitar.com/articles/ ... russ-rod-1
Note these are addressing rattley rods, but will also damp the rod, so should stop deadspots, too.

1c) Headstock plate - uses same screws as tuners - holes in plate can be countersunk so screws have longer thread in the wood
Image

3a) O-ring under trussrod nut - apply a touch of pvc or other weak glue to the underside o-ring to make it stick to nut temporarily while you screw it back - must push the nut as you turn to make the oring squeeze on to the rod
Image

O-ring shown fitted onto end of truss-rod
Image

3b) Wire in truss rod cavity (if there is a gap for it to fit) - I twisted some copper wire with an electric drill to make it stiff
Image
Last edited by noplanb on 12 May 2018, 16:57, edited 2 times in total.
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slowlearner
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Re: Dead notes and the Truss Rod

Post by slowlearner » 12 May 2018, 14:57

I can't specifically comment on a general thing like this, because every bass if different. However, I'm genuinely surprised you're linking it to the truss rod. I've never ever experience what you're describing. I have experienced rattle or a non-operative rod, but not this. Could you give us a specific example of this issue? Some pics? Maybe even a recording of the dead notes specifically caused by the truss rod.

Personally, I've noticed dead notes seem to be more prevalent in one piece necks (fender style) on bolt-on basses. Fretless basses seem to make the dead notes more prominent. I've had experience of dead notes on laminated necks, but they weren't as severe.

I've also noted that the dead note seems also to be dead on a number of strings. So, on one bass, it had a "D" that was dead on the G string. I noticed, the octave D was dead on D string. Also on the A string the high D was not great. Was it caused by the trussrod? Impossible to know. It was a good instrument. The bass in question lost all of it's dead notes when I put high tension flatwounds on it. Instantly, they disappeared (or seemed to).

Somewhat curiously, the 6 string I've just finished seems to have a slightly weak "D" on the B string. Not terrible, but not quite as strong as the other notes around it. This is interesting to me as the bass has big strings and a HUGE scale length. I've not noticed any other dead notes on the bass, just the one. The last fretless I built at 32" also had a slightly weak "D" on the B string with flatwounds, but with roundwounds there was no issue at all.

On a related note, every upright bass has a "ghost note" somewhere on it. Some are in a perceivable spot. Others not. On my bass it's the 12th fret position on the A string. Every other note on the bass is fine. The same "A" on the D and G strings is fine, but on that string, it's a little dead. Acoustic guitars also have similar issues. So, even if you say, "it has no dead notes," in reality, the dead notes are just where you're not playing them or hearing them.
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noplanb
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Location: Adelaide

Re: Dead notes and the Truss Rod

Post by noplanb » 12 May 2018, 16:55

Yes - some pics are added of some of the things I've tried. I'm going to try a few others.
I've presently got an o-ring and 2mm long sleeve of pvc tube under the trussrod nut of my Fender TNL - it turned it from unplayable to playable, excepting for a dead 2F#. I plan to try a couple of other non-invasive things, but I might try a remove-the-dot on a lesser bass first. Note that this bass when played live would have a mix of notes across the fretboard that would either boom or go 'thop' (or something....). Now its one step short of 'lovely' !

Each of the photos above had a definite, useable effect. I still have them, bar the brass block - the wires in the rod channel did it instead!

I define a dead note as one where you know it is dead, so you hit it a bit harder when you play it in a piece.
Anything that changes the mass or stiffness of any part or thing on the neck, and causes a change to any resonant dead spots, fits the above hypothesis
.
Yes - numerous dead notes tend to dissipate with one of the treatments mentioned. I suspect the dead-resonance is still there as you say, but either shifted to a less sensistive frequency for the rod, and/or its bandwidth is widened with the amplitude lessened. Once it hits the 3dB variation to other notes we wont notice it- much ;)

You can test the resonance thing simply by putting a metal clamp on the headstock using some felt or cardboard to guard the jaws. If the dead note has changed - well, it is what it is. Next try one of the above methods to see if you can fix it permanently.
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