Connecting the voice coils of each driver in parallel (+ to +, - to -) and the drivers themselves in parallel (+ to +, etc.) will result in the following impedances:
Dual-6 Ohm Subwoofers: 1.5 Ohms
Dual-4 Ohm Subwoofers: 1 Ohm
Dual-2 Ohm Subwoofers: 0.5 Ohm
Dual-1.5 Ohm Subwoofer: 0.38 Ohms
Or here
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Lee - MECP Certified
"Any advice given on this forum is intended for helping and assisting the end user with their issue at hand. Personal saftey is important when working on any vehicle."