Originally posted by the fool
then how do they set up those old martins and some of those classical guitars that don't have a truss rod?

That I don't know. I just know that a truss rod is meant to compensate for string tension. The strings on your guitar pull the neck toward the front of the guitar, while the truss rod pulls the neck back towards you (if you were holding it) to compensate. If the neck becomes warped, I don't know what you can do to fix it besides replacement.

Antique guitars are not my forte. But I believe over time, older acoustic guitars start to bubble on the body because of string tension. Lordathestrings would be the one to help you out on this topic.