I asked Bob about the fact that in my earliest (of three) pair of ALS Silvers (CT woofers), and in the Originals (and I presume the first Plats, too), there are no openings cut in the rear "baffle" frame in the way they were always found in the later Silvers and Platinums. How does this effect the bass? "Not at all", said he. Then why cut them? "The solid side of the rear box toward the ribbon caused an unforseen intermodulation up in the midrange ", he said (the ribbon research had all been done with the boxes off, so the problem was missed). So I should cut out the holes in the pair that lacks them? "Yes, definitely. Better sound."
I will be doing my own soon, and luckily I have both types side by side, so by copying the measurements from the newer style to the CT type I can duplicate the cutouts. If anybody wants to do theirs, I will post a drawing with dimensions as soon as I hear from a few interested parties. There is one opening opposite each woofer, so three or four per side, depending on your model.
If you feel along the cloth cover on the RIBBON SIDE of your rear baffle and there are already oval openings, forget it: you're good. The other side is never cut out.