The M500's restoration is finished and they're tri-amped at 1.1 kHz and 7.5 kHz. While they're sorta-kinda-maybe usable up to 20 kHz according to Altec, they start to roll off just over 12 kHz. So an Eminence ASD-1001 HF driver with an Eminence APT-200S bi-radial horn were added to make the system go all the way up 20 kHz.

Initial listening tests are very positive. The MR994A horn and 909-8A combination present a wide soundstage and very smooth life-like sound. The 3154 woofer is a wolf in sheep's clothing. It's usable from 45 Hz to 1.3 kHz (1.5 KHz with help from a PEQ). Yea, you can get it to do the 2 kHz spec but since the horn can be crossed as low as 500 Hz, it really isn't necessary.

This speaker system shows a lot of promise.