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OK, trying to post a few pictures of the Ultra to help fill out the project. The views are self explanatory.
The woofer location is just off center vertically to help minimise rear standing waves, ... and high enough off the floor to minimise floor bounce. One could move the woofer upward closer to the Vifa.
There are many aspects to any given design. With the ultra's design, if the woofer were mounted as low on the baffle as possible, the woofer - tweeter vertical separation would become a major issue. Maintaining the Vifa at around 38" above the floor for me IS very important to the overall performance and power response of the system. There is a limit to crossover correction capability relative to vertical separation of the two drivers. Somewhere around 15" of center to center separation seems to be the limit. Otherwise major lobing issures begin to degrade the SQ. The accoustic crossover point is centered around 550 Hz, but the up woofer contribution reaches over 1 KHz, although it is down about 18 DB at that point. The Vifa is contributing down to about 175 Hz. (Down about 24 db at that point in overall power response).Larger separation was not possible when maintaining a simple crossover topology - cost. So the best trade off was to mount the woofer up higher. With the woofer contributing well into the mid range, mounting it higher gets it's mid range output closer to the overall speaker axis. And with an OB woofer that is playing into the mid range, one has to deal with rear radiation issues including absorption than can occur with residential carpeted surfaces, front also.Bottom line is the woofer is up where it is for a number of reasons. Mr. Allison is just fine when operating in a traditional monpole environment..