The drivers seem to be a variant of Monacor's SPH-175. They look slightly different
to the current SPH-175's, and measure even more differently. The tweeter is the Vifa D20TD-05-06.
The drivers are now over 7 years old, and this shows when I measure the T/S parameters
in the way of large inconsistencies between drivers.
I decided to pair them as best as I can and plough on regardless. I used my dedicated
DIY speaker measurement clamp to hold the drivers firmly
for impedance measurements, and used Speaker Workshop to do the measurements.
The T/S measurements were averaged out for the four midbass drivers and this was the result:
* Parameters taken from current SPH-175 spec sheet.