Not specific to Dingwall but in other threads I’ve seen comments indicating that CF stiffening bars or rods add weight to the overall structure. If weight savings was your primary concern then leaving out the reinforcement would be preferable.
My one and only Dingwall is plenty light and balances just fine, so I’m perfectly happy with whatever Sheldon is doing
Exactly.
No competent designer is going to build a huge amount of mass into a neck, regardless of whether they're using wood or carbon fibre. We're building a light, resonant music instrument here, not a girder bridge!
My friend Tony builds very fine acoustics. He uses CF reinforcements in baritone guitars, because they sound better with than without. Like Sheldon, he's just trying to stabilize an unusually long neck and control unwanted resonances.
The rectangular bars Tony gets from Luthiers Mercantile aren't very large, maybe 3/8th's by 1/8th inch?
When we put them in the bass I built, I found that they weighed almost exactly the same as a piece of rock maple the same size. Both had a linear grain structure, and sounded like wood when tapped on a hard surface.
Both are
very different to a piece of steel of the same dimensions- much lighter, and they don't ring with the unrestrained "ping" you get from steel.
The most discernable differences between maple and CF are that a.) if you flex the CF between your fingers, it feels noticeably stiffer than the maple, and b.) if you tap the carbon, the pitch it gives off is slightly higher.
Tony loves to demonstrate the same thing with Brazilian rosewood and Gaboon ebony bridge blanks. If you drop them on the floor at the same time, Brazilian bounces higher, with a more lively and high-pitched sound. Ebony makes a dull clack. He can't use Brazilian bridges in export instruments any more because of CITES, but they're great in domestic instruments.
However, it's important to understand how different these two applications are:
Compared to an electric bass neck, the top of an acoustic guitar weighs next to nothing. Also, the bridge is at the most critical point in tone production on an acoustic guitar- right where the string vibrations are driving that thin, light spruce or cedar top.
You're also talking about conserving finer, higher-pitched vibrations, of a much smaller amplitude than the ones you get from a bassist whacking on a .130 B string...
The neck of a bass guitar is massive in comparison. The mass of a couple of thin carbon sticks relative to the rest of the neck is inconsequential. Also, the neck is pretty far removed from where the player is striking the strings- it's purpose is more structural, than about tone production.
What matters isn't the mass, so much as that subtle increase in stiffness, along with the slightly higher resonant frequency compared to the wood you removed. The designer isn't attempting to damp out or kill resonance, like wrapping the neck in rubber, or hanging a lead weight off it. You're just smoothing out any unwanted peaks or cancellations.
Once you bond those sticks into the maple neck, you get a single assembly with a broader Q than it had before lamination: peaks in the resonance of the neck at specific frequencies are going to be tamed sightly, resulting in a more even response, and less likelihood of dead spots or wolf tones. It's really no different than laminating contrasting stripes of a stiffer wood into a 5-piece neck.
It's also worth remembering that a Wenge fingerboard is pretty massive compared to two little bars buried in the middle of the neck. Once again, the CF bars are about fine-tuning. We're talking about VERY sublte differences, with or without.