I started narrowing down my selection by looking at what driver size it would take to play adequately low and loud. In my mind, I knew that a 4" driver was the smallest I wanted to use. Yes, there are many surround systems that use 3" drivers, but I just don't feel that they play loud enough or low enough for my desired playback level. So, looking at the 4" drivers, I was immediately drawn to the Audax AP100ZO shielded Aerogel woofer for its combination of relatively low Fs, relatively high QTS (meaning it can be used in a sealed box), and its healthy XMAX. From modeling my measured specs for the driver, the low-end extension looked good and the maximum SPL was respectable.

Next, because I was using a small 4" driver as the woofer, I knew that I wanted a very compact tweeter, and that it didn't need to play exceptionally low. Staying within the Audax family, the TM020J3 was a perfect choice for its clear highs and compact design.