How thick should the front baffle of speakers be?

fsonicsmith, it does not have to be eliminated. There are two types of distortion, Linear and non linear (this is psycho acoustic babble now, not my own) Linear distortion is alterations in frequency response which are very noticeable. Enclosure resonance would be in this category. Non linear distortion is IM and Harmonic distortion as well as mechanical distortion, buzzing, rattling and so forth. Studies (not mine) Have shown that Humans will tolerate non linear distortion levels up to 20% under certain circumstances the reason being that the distortion is being masked by the music. Non linear distortion is also more noticeable at lower volumes. This could be why some of us like higher volumes until system overload. This is the reason MP3 files sort of work. 
Frequency response is now completely manageable in the digital domain. You can correct virtually everything including enclosure resonance with room/speaker control. And, according to the psycho acoustic folks non linear distortion does not matter that much until it reaches ridiculous levels. Probably why we tolerate listening to such crude devises as loudspeakers. I guess their message is get full spectrum room control and be happy.......right.     

brayeagle, that was a Warfdale in the old days. Cost too much to ship the things. 

Many designers are using smaller woofers, they understand that the back waves often bounce back and right through the diaphragm. Not good. Those large woofers 10" and 12" suffer the worst. Not to mention the listener. 

The only reason small woofers proliferate these days is that designers can orient them front-facing and still make the cabinets slim, and hence decorator- and spouse-friendly. I've heard multiple small woofers in speakers vs. a 12", and preferred the 12" every time.

Well I dont think a speaker can sound accurate with one genre of music and not another. Harbeth's lossy cabinet represents the worst possible approach to this problem in my opinion.