compression driver + 15 inch or large piezo horn + 15 inch


What is the difference between a 1 inch compression driver + 15 driver; and a piezo driver with a large horn[rectanglar horn].

Eminence Delta pro 15 300w rms bass driver + Eminence pds2002 1 inch compression driver 80w rms + Eminence pxb2-1k6 crossover.

OR

Eminence Delta pro 15 300w rms bass driver + Motorola ksn1140 piezo driver + CTS 15 inch x 5 inch exponential abs plastic horn.


Also I've seen some new Peavey 2 way cabinets featuring 4 ports.why would a normal 2 way design have 4 ports.I thought only bass bins or subwoofers have that many.



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