slowmotion,
 
 I think the ultimate length of the upperbass horn is 3”- 4” throat. With longer horn it would be very complicated to time-align it as the horn will mask out the MF driver.  The ultimate driver for upperbass should be a compression driver, low to medium flux, with no face plug, most likely with aluminum cone and resonant frequency ~20-50Hz below the horn rate. I personally do not know such a driver, if someone do then let me know….
 
 The Cat |  
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