Hi friends:
I'm always cautioning my doc students about the dangers of trying to isolate a single variable--or even a group of variables--that account for a phenomenon. In the real world, there many extraneous variables that are difficult or impossible to control.
Guitar setups are prone to extraneous variables as well. Something that appears to be so simple on the surface, such as intonation, becomes extremely complex when you factor in the extraneous variables. All of the following variables will have an impact on the accuracy of intonation on a guitar:
First, the strings travel through one, two, or three magnetic fields before reaching the bridge. These magnetic fields can be manipulated by adjusting the height of the pickups with a nearly infinite number of variations.
Second, there are all kinds of string guage combinations from many different manufacturers that can be fitted to a Rick 12 string. Furthermore, the consistency of string guages from the nut to the bridge may vary infinitely.
Third, the amount of relief in the neck is going to effect the length of the string from the nut to the bridge. The more releif, the shorter the length.
Fourth, the height of the strings at both the bridge and the nut will effect their overall length. Raise either of these and the string length from the nut to the bridge will get longer.
Fifth, the angle of the neck in its relationship to the top of the guitar will have an impact on string length.
Sixth, the amount of pressure that you place on the strings when you fret them is going to impact intonation. This is another continuous variable that has a nearly infinite number of levels.
Seventh, the amount of pressure that you put on the neck of your guitar with your fret hand becomes another continuous variable.
Eighth, and most importantly (and peplexing, I might add), all of these variables, plus many more that I have not even thought about, INTERACT making such a simple physics and math problem (intonation) difficult, at best, to solve.
So, in reality, we are dealing with a series of extraneous variables that often require compromise, as several of you have suggested, when we are setting up our guitars.
I opted to fit a 12 string saddle to my 360/12 because I knew that I would have alot more control over intonation of the octave strings (simple math and physics!). I made sure that the relief in my neck was the way I like it (very little!), and I adjusted my pickups to my personal tastes, and then I adjusted my string height before tackling the intonation issue.
I decided not to move my bridge plate because my intonation was fine without doing so. Yes, my low E string's saddle is close to the edge of the bridge, but I was able to get a small spring between it and the flange and still have the string intonate properly.
I check the intonation on occasion, usually when I change strings, and I am impressed with how unstable it is from string set to string set. I am sure that my strings pick up a small amount of magnetism over time and this can effect the stability of intonation. I am also certain that the relief in my neck is constantly changing (I live in Colorado where the humidity is extremely low).
Even with all of these issues, I love the sound of my 12 string Rick. It is never perfectly in tune and perfectly intonated (perfection is impossible in its truest sense), but a with good set of Pyramid strings and the 12 element saddle, I can get pretty darn close...without moving my bridge plate! I hate the thought of drilling holes in my guitar. I simply will not do it to s guitar for which I paid over a thousand dollars! If there is a problem that cannot be corrected to be within acceptable limits, the guitar goes back to the store. Those acceptable limits may vary from one individual to another. What is acceptable to me may not be acceptable to you.
Here is what I do know for sure. I have been reading the excellent text by Babiuk entitled "Beatles Gear" and what I find is that George Harrison loved is 12 string Rick. He was able to make great music with it, and he was not thwarted by intonation problems. I recently bought the Byrds' CD that was recorded live at the Fillmore in 1969. Again, the great 12 string playing of Roger McGuinn was not tainted by a guitar that suffered from intonation problems. These guitars make great music because, in the hands of competent musicians, they are FABULOUSLY designed and constructed guitars that have withstood the test of time. The Rick 330/340/360/370 gutars have an instantly recognizable trademark sound that transcends any inherent design problems.
I am all for doing the best setup work that I can, but at some point it becomes an unhealthy obsession that can easily overshadow the fact that I have a great guitar that deserves to be played and heard by others.
Here is a link to a photo of my 12 string bridge.
http://www.coe.unco.edu/jeffbauer/bridge.jpg
Sorry for the length of this post--professors are notoriously long winded with little of value to say. I am no exception:-)
--jeff
http://home.attbi.com/~drjeffreyb