In fact, I found that while taking the tweeter grill OFF meant I could hear it more distinctly...ie, more detail...I also found that the diffusion caused by the grill helped in 'blending' the treble back into the overall presentation better...it seemed more coherent this way. The question is whether I would remove all the other grilles and leave the Tweeter grill on.
...only one way to find out I suppose...
OK...I just did it. Grilles off, Grilles off other than tweeter. With Grilles off, you realize that the trumpet, sax are not quite as present in the room...you lose clarity. However, with Grilles ON, you get a slightly more coherent sense to the music...each cone is less evident. Sure, its because we have lowered the level of detail from each cone, but it is not a tragic loss of detail, and in truth the cones 'glare' a bit on certain recordings when left exposed.
Taking off Tweeter grilled is a bit much even though my tweeter is a much much later generation Focal with the back wave redesign (in fact the tweeter is only a year old...so probably something akin to the Maxx 3 tweeter).
Grilles are back on...and staying there. Plus Generation 1 was ugly without grilles because these grilles are velcro'd on...none of the more elegant drilled holes. Experiment finished.