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ScanSpeak Discovery Line 30W/4558T 12″ Subwoofer – 4 ohm

Aluminum Cone, Black Anodized
Fiberglass/Paper Sandwich Dust Cap, Black Coated
56 mm peak excursion – 25mm linear (X-max)
Aluminum Short Circuiting Ring
Aluminum Pole Piece Extension to reduce distortion and power compression
Titanium Voice coil former
Vented cone / dustcap
Nomex spider
Low damping rubber surround
Litz wire woven into the spider

Suggested box alignments: 

One cubic foot sealed for use in autosound systems.
One cubic foot sealed with a plate amp and boost for use in home systems.  With our KG5230 the F3 would be 38Hz.
The 30W/4558T and the 30W/0-00 passive radiator in a 2.5 cubic foot box should be 3dB down at 30Hz.
For a vented box of 2.5 cubic feet, 3″ vent by 11″ long, your F3 is 27Hz.