Horn loading comes more from HT and professional audio....it is the most efficient way to load a speaker. But in the car audio world it is very hard to fit a horn loaded enclosure into vehicles due to the enormous sizes. Poly fill can be used in any enclosure...it just makes the speaker "see" a SLIGHTLY larger volume than actual. Also lowers efficiency a little bit.
Efficiency as in sounds worse at overall bass response? Because i thought it was to SLIGHTLY improve response and low tones? Wouldnt the poly-fil be blasted through my 4 ports on top of my box or is there a way to keep it still?