Acoustic Guitar Construction

Just saw a video on a necksetting technique, and the neck being fitted had a truss rod and channels for two carbon fiber rods flanking the truss rod, one on each side of the truss rod in its own channel. I admit I'm thick inna head, but I can't understand why a truss rod is being installed, which will be use to bend the neck, in the same neck as a pair of carbon fiber rods, which are going to do everything they can to resist bending. Anybody able to address this? I gotta be missing something.
Thanks very much.

There are long mail threads in many guitar forums arguing for\against the value of CF rods in the neck as their position near the natural axis or something or another limits their value. In the last thread I read the conclusion was that they may make the neck 10% stiffer. I use them and the truss rod has no problem bending the neck. I can not argue that they have any value. I use them because that is how I was taught to make a neck.

John

My friend Dave (dhlutherie here on the forum) and I have been cooresponding regarding the problems that come up because a neck is too stiff to allow the tiny bit of required relief (forward bow). A hefty two way truss rod might be a good way to tweak in the relief and of course the neck could be made thinner. To this point I don't think I really understand how carbon fiber reinforcements and a truss rod lends to the adjustablity issue. Now CF on a non-adjustable classical guitar makes perfect sense to me since the relief is machined on the fingerboard surface -- a slope from nut end to bridge end. $.02