SP4 Heavier SP4 More mounting depth SP4 4" coil vs 3" on N2 SP4 10" spider and higher mechanical linearity than N2 SP4 More long term thermal stability SP4 Sealed capable vs N2 ported only N2 More motor force N2 Inductance ring that balances the inductance swing better SP4 Slightly lower overall inductance than N2 N2 Well... its cool because its Neo N2 It's expensive because its Neo (and constantly increasing in cost) SP4 Slightly higher Xmax (coil limited) SP4 Lower FS for those that think it m