15 VS 12 Inch Subwoofer: What's the Performance Difference?
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18 Sound 15W750 Subwoofer Speaker
Sundown Audio X-18 V.2 D4 18" 1500w RMS Dual 4 Ohm Subwoofer Speaker Basket for sale online | eBay
Bigger is Better......Or is it? 12" vs 15" vs 18" vs 21" (PA Drivers) - Techtalk Speaker Building, Audio, Video Discussion Forum