Anyway, a 0.5mH coil was added in series with the midwoofer, which brings down the presence above 1kHz just a little bit. You can certainly add it to the older speakers - The difference is very slight but noticable. But the coil is really only intended to be used with the newer midwoofers, and I compared them with and without the coil in the post called "Coils on one π's and two π's."

This is the only circuit difference in the old and the new models - The addition of 0.5mH coil in series with the midwoofer. You can get a 0.5mH coil from Parts Express, part number 260-723.