Theory can sometimes correlate to real world performance...but when someone claims X sub has 2 mm more xmax than Y sub...when are you going to use those 2 mm? Will the distortion levels that differentiate because of the longer throwing woofer be audible? No.
Of course things on paper help greatly to correlate to real world expecations, but there is a limitation to how much it helps.
Theory actually correlates very well with the real world. Simply showing an extreme example of two drivers with very little difference (in both measurable and audible terms) hardly proves your argument.
Not ALL measurable differences are audible. I don't believe anyone claimed that they were in this entire thread, so it seems to refute a claim which was never made.
Audibility is subjective, so speculating about it is often a poor idea. Objective data is quite easily interpreted, and by its very nature is free of any bias. It's data. Period.
Displacement VERY accurately predicts differences in linear output across a driver's usable bandwidth. Now obviously for the test to be of any validity we must hold all other factors constant.
One problem is that many people conduct piss poor comparisons. The results of these poorly designed "experiments" disagree with what Science would predict, and then they ignorantly fault Science, rather than their inability to conduct a valid test, which is the REAL issue at hand.
As far as driver linearity goes, a few mm of xmax isn't likely to make much of a difference when we're comparing drivers with such high levels of displacement, but that certainly doesn't mean that all or even most xmax differences won't result in an audible difference.
Another highly irritating problem is that many people try and generalize all objective data as "what's on paper", and for God knows what reason, they assume that a T/S sheet is the epitome of objective evaluation, and furthermore try and rebutt the claim that a T/S sheet provides all necessary data for objective evaluation, even though no person, who has even a mediocre understanding of the subject, would ever make such a claim. It's a bizarre phenomenon that continues to baffle me, but time and time again I hear the same tired, baseless "argument" rear its ugly head.
So, in summation:
Will a T/S sheet tell you everything you need to know about a driver? NO.
Will a detailed objective evaluation of a driver be able to? Yes.
Do most people even have the faintest idea what that is? NO.
Do the Laws of Physics cease to exist in your car? NO.
Is comparing woofers across installs intelligent? NO.
Is it even meaningful at all? NO.
Is making conclusions about a DRIVER based upon hearing it in AN INSTALL very intelligent? NO.
If a woofer gets louder than another at a bass farting competition, does that mean the driver will play music more loudly (across the entire bandwidth) as well? HELL NO. YOU SHOULD BE SLAPPED WITH A 2X4 IF THIS THOUGHT EVEN ENTERS YOUR MIND.
