neck straightness and mwaa

open strings · Post by **open strings** » Fri Jun 01, 2007 4:43 pm

Hi all, I was hooked up with you guys a couple months ago while I was doing a de-fret job on my old bass.

First I wanted to say thanks for taking the time to help me out. Your answers to my questions were very helpful.

The project is pretty much done. I did a number of mods besides the de-fretting. And I have to say it's turned out nicely.

I have another question now. My most recent effort was a truss rod adjustment to reduce some extra back-bow. That went fine, but now it seems my mwaa is diminished. Does it make sense that a straighter neck would generate less mwaa?

I restored the neck to it's previous bow to see if it was just my imagination, and got the mwaa back. Bridge saddles have been up and down through all this, but I can't seem to get low action with good mwaa.

I'd appreciate any input!

open strings · Post by **open strings** » Fri Jun 01, 2007 4:50 pm

just as a follow-up comment, what I report about neck straightness and mwaa seems opposite from other posts on this site. I wonder if I'm missing something...

FretLessSince68 · Post by **FretLessSince68** » Sat Jun 02, 2007 4:50 am

In my experience, a straight, or nearly straight neck/fingerboard is the best for Mwah. If you have back-bow the instrument will be pretty much unplayable due to notes choking (damping oscillation) unless you raise the action way up which will also kill the Mwah.

Back bow is a curvature of the neck that is in opposition to the bow normally imparted by string tension.

To test for back-bow: With the instrument tuned to pitch, when a string is held down at both ends of the neck there is no gap between neck and string (test one). Additionally, when a string is held down at one end, and you are in the process of pressing down the other end, the string will contact the fingerboard BEFORE it is pressed down completely (test two).

If your fingerboard is straight, the first test (above) will be true, but the second test (string contacts fingerboard before fully depressed) will be false. A good straight edge will reveal most problems.

Whereas with bow, when holding down a string at both ends of the fingerboard, you will see a gap in the middle between the fingerboard and string = bow or relief.

Back bow is usually caused by changing to lower tension strings without adjusting the tension (truss) rod for the new type of string.

In the case of a defret job, back-bow can be induced by inserting material (filler strips) into the fret slots tightly, or using a glue that causes swelling. This forces the neck to take a curve opposite the expanded frets slots (back-bow).

If you have back-bow, the user often raises the bridge to reduce or eliminate the choking of notes. This will kill Mwah and you may also have areas with excessive buzz, usually toward the nut.

I would reccomend that you put a straight edge on the finger board and see if you can determine any problems. Back light it and look for gaps, dips, peaks, S bends, twists, or other imperfections.

What strings are you using?
Did you change string type?
What fingerboard material?
Single acting (conventional) truss rod, or dual action?
One truss rod or two?
Did you back off the tension on the truss rod(s) before inserting any fret fillers, strips, or laminate?
If you inserted fret slot filler strips, what kind of glue used?
Do you use drop tuning or non-standard tunings?

open strings · Post by **open strings** » Sat Jun 02, 2007 9:56 am

hey FS 68,
First I have to apologize for something...using the wrong terminology for the bow... the bow is toward the strings not away. just a bow, not a back bow. So sorry to send you off in the wrong direction. All the information you gave was useful though.

your questions:
What strings are you using?: old old nickel rounds
Did you change string type?: kept old ones on. Cheap,ain't I.
What fingerboard material? Maple polyurethane coating
Single acting (conventional) truss rod, or dual action? single
One truss rod or two? one
Did you back off the tension on the truss rod(s) before inserting any fret fillers, strips, or laminate? no. didn't seem to matter, as the filler has stayed intact through the truss rod adjusting.
If you inserted fret slot filler strips, what kind of glue used? no strips. Used a product called PL Professional Wood Filler. A paste that dried hard and I think worked very well.
Do you use drop tuning or non-standard tunings? just standard. some times drop D.

Currently along with the mwah issue, I'm trying to chase down the source of a rattle in the headstock area I get when playing only certain notes on the G string. I was afraid maybe the truss rod was the source, but judging from the neck response when I give 1/4 tweaks, the rod is ok.

thanks again.

point19 · Post by **point19** » Sat Jun 02, 2007 10:02 am

Check for a loose nut or loose tuners for that rattling..... those are common sources.

FretLessSince68 · Post by **FretLessSince68** » Sat Jun 02, 2007 5:41 pm

Regarding noise: A likely source of rattling or noise that seems to emanate inside the neck is truss rod vibration. Even under tension it normally vibrates and if it contacts the side, top, or bottom of the truss rod channel you will hear it. The usual fix for this is to take the truss rod nut off and slip a felt sleeve over the entire length of the truss rod.

Some instruments do not have much room in the truss rod channel so it may be difficult to slip in the felt damper.

Truss rod vibration is usually not heard amplified so you will probably not notice it when actually playing. So not really a big deal if it is truss rod vibration.

There are other potential sources for the type of noise you describe such as a loose, or not fully seated screw(s) that permits a part to resonate. Check all screws, check bridge saddle adjusters.

Here is a link into TalkBass dealing with sympathethic noises.
http://www.talkbass.com/forum/archive/i ... 47993.html

Back to your initial problem: Mwah goes away when you adjust the neck to be straighter and/or lower the bridge.

Your strings are probably not the problem.

I suspected that you were really talking about bow, that's why I included a back-bow definition.

OK, this is a much better situation (much, much, better). Severe back-bow is difficult to manage.

The situation you describe is not optimal and I see why you are concerned. I suspect that the neck may have a slight "S" bend, or the neck takes a bend where the heel ends. This is fairly common on basses with slim necks.

Put a precision straight edge (or the best one you can borrow) on the finger board (tuned normally) and see what shows up. Use a back light to help reveal any defects. Also sight down the neck and see if you see any defects, although this visual test is less precise, an experienced person may be able to spot a problem more quickly.

Please describe the make and model of your instrument.
What do you see when looking at the fingerboard with a straight edge?
How much relief do you now have? (usually measured with feeler gauge)

By the way, Polyurethane made for flooring applications works very well for me.

open strings · Post by **open strings** » Thu Jun 07, 2007 8:45 am

thanks for the response. It helped to tighten the machine head screws, so that was the main issue apparently. I'll do the straightedge/backlight inspection this weekend, especially because I did so much work on the neck defretting it. will guage the relief too. thanks for giving me things to try. Tha bass is a Saga kit model I've had for 25 years.