I love my Titanic. It hits like a monster. Probably because it is a monster. But if you already have an enclosure I'd consider the Dayton RSS390HF-4 15" High Fidelity Subwoofer. It goes lower than the Titanic, has less distortion and even costs less. It just doesn't handle as much power.
Specifications: *Power handling: 500 watts RMS/800 watts max *VCdia: 2-1/2" *Le: 1.00 mH *Impedance: 4 ohms *Re: 3.3 ohms *Frequency range: 18 - 800 Hz *Fs: 18 Hz *Magnet weight: 150 oz. *SPL: 90 dB 2.83 V/1m *Vas: 9.55 cu. ft. *Qms: 3.10 *Qes: .49 *Qts: .42 *Xmax: 14mm *Dimensions: A: 15-5/16", B: 14-1/8", C: 6-1/8".

http://www.partsexpress.com/pe/showd...number=295-468

But if you want more than 500 watts RMS then the Titanic is a great choice.