Is this a disadvantage to carbon fiber?

[Dave Bagwill]

Just so I'm clear:

1. Carbon fiber rods or d-tubes or whatever for neck reinforcement - do the rods allow for compensation? If they do bend to allow for adjustment, what is the purpose?

2. Carbon fiber braces, sandwiched with wood or not - if they are that stiff, how can the top move as freely as it would like to?

I don't have a dog in this, just trying to learn.

Thanks

[John Parchem]

Just so I'm clear:

1. Carbon fiber rods or d-tubes or whatever for neck reinforcement - do the rods allow for compensation? If they do bend to allow for adjustment, what is the purpose?

You can use a truss rod with carbon fiber rods. There is a bunch of debate about the rods being useful. The mechanical analysis I saw from a doubter showed that the rods properly placed "only" increased stiffness in the neck about 10%. The carbon is lighter than the wood it replaced so I will take 10%.

2. Carbon fiber braces, sandwiched with wood or not - if they are that stiff, how can the top move as freely as it would like to?

There is an implication in this question that stiffness is a sound killer. Yet when a top is picked one looks for a combinations of high stiffness and light weight. A carbon fiber supported brace can make a smaller\ lighter brace and have the same stiffness of a heavier brace.

kinetic energy is a combination of mass times acceleration. A vibrating instrument is constantly accelerating as it is changing directions at its vibrating frequency. Thus accelerating the mass of the top and braces is using up energy of a string pluck. If one has a plate the same size and stiffness but less mass (weight) more of the strings energy can go into making sound instead of accelerating the excess mass.

One can and some do go all fiber and get an instrument that performs great all fiber violins and cellos are being used by real musicians. I have played all fiber guitars and they do not seem as rich with sound color to my ears. But we do not have to go to absolutes, One can use CF to enhance a desired characteristic of a wood instrument.

[ken cierp]

CF adds stiffness and of course depending on how much is used will determine how much force the truss rod will have to apply to change the curve of the neck. Personally I would only consider using it on a 12 string mostly to help prevent twist that sometimes occurs because of the inbalance of string tension on the bass side. And I would not build a bass guitar without it. I know nothing about the +/- regarding acoustics. Steve Kline claims adding weight to the head stock improves a guitar, Siminoff claims making the neck stiffer does the job -- I assume both are supposed to control the tuning fork effect?

[Dave Bagwill]

Does CF as a brace, or sandwiched in a brace, inhibit top movement? Thanks, I get that it is stiff and light, good things; so I'm guessing that the CF is radiused the same as the braces, but does it move the same as all wood braces, and is that a good thing?

[ken cierp]

Does CF as a brace, or sandwiched in a brace, inhibit top movement?

Maybe -- if you made "brace sandwich" the same width as a standard Spruce brace likely it would. If you used Balsa and CF you get the advantage of very light weight (which is what you are really looking for) same glue surface and split prevention for the sound board. I am thinking there is little precidence to determine what sizes work best and you sorta have a crap shoot. Make the top too stiff and it might sound way bright or worse like you have your hand pushing against the top. I agree with John the CF guitars (at all price points) without EQ are far from what my ears have come to expect.

[Robert Hosmer]

Likely to be another one of those never-ending controversies.

Which came first- the chicken or the egg?
Regarding the use of CF in the neck, what was the original purpose of the truss rod- increased stiffness or adjustability?

[ken cierp]

Stiffen the neck -- Martin used "T" bars and square channel metal until the late 1970's -- no adjustment.