Ummmm... "spare time"???? What's that? I think I read about that intriguing concept somewhere, and it sounds like something I should have! Where can I get some? Do they sell it in Home Depot???... in your 'spare time'
I haven't asked Glenn for all his reasons, but one of the things that I'm starting to appreciate with having the intersect further back, is a wider sweet spot at the console. If the "cone" ends right behind your head, then as you lean left or right you can find your self with one ear off-axis and edging outside the direct field of both speakers, while the other is getting right into the middle of the combined field. With the speakers aimed slightly outside your ears, for the more rearward intersect, then as you lean left and right, you are moving you ears more directly onto the axis on one side, while still staying in the combined field on the other side. OK, so its a subtle effect, but I have noticed it, so it is worth taking into account. The same also applies to front/back movement: If the intersect is close behind your head, then you don't need to move your head too far back to be through it and out to the other side, where the left speaker is now aimed more at your right ear, and the right more at your left. Especially if you had to increase the toe-in to 45°, for example, due to the room dimensions.
In a big room with the speakers far away, these effects probably aren't very important at all, but in a small room things are different. And of course, the closer you are to a speaker, the less you have to move to get off-axis. For example, at the extreme case of having your ear just 6" form the tweeter, if you move just two inches to the side you are already nearly twenty degrees off axis, and well out of the on-axis field. But if your ear is 60 inches away and you move it 2 inches to the side, you are less than two degrees off axis, which is not important.
Of course, all of the above depends on the directional behavior of the speaker itself (dispersion angles). For a speaker with wide dispersion angles across the entire spectrum, the effect is much less. But in that case, you need more careful room treatment, since the speakers are "illuminating" more of the walls with the wider cone, so your first reflection points (for example) need to cover more area, and your ray-tracing (if you are doing RFZ) needs to consider higher angles. On the other hand, speakers with only narrow on-axis fields at higher frequencies don't illuminate so much of the walls with the highs, but they do make your sweet spot smaller, since you can't move your head around as much and still stay on axis.
So there's a lot of factors here, and a couple of others that I'm still looking into. Each effect by itself might be small, but add them all up and it definitely seems that having the intersect further back makes sense.
Plus, there's an interesting study I read a while back (but can't find now!) that showed how most engineers tend to work with their heads a little forward of the supposed "optimum" point of the sweet spot, most likely subconsciously: they just work where it sounds best. There has to be a reason for that!
Glenn might also have other reasons for his recommendation: I'm wondering if he is around? It would be good to hear his comments! And John's, and Rod's and Andre's...
- Stuart -
haha just kidding...PLEASE feel free to chime in at any point about anything...it really helps keep my motivation up! Not to mention I've looked forward to the day that this thread might take on a life of its own... 
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