https://www.stereophile.com/content/snell-music-cinema-home-thx-reference-system Specs are supposed to be: SUB 1800: reflex-loaded (fourth-order) subwoofer with 18" cast-frame driver. Frequency response: 17Hz–80Hz ±2dB anechoic. Impedance: 8 ohms nominal, 7.5 ohms minimum. Sensitivity: 88dB/W/m. Amplifier requirements: 90–400W. Dimensions: 45" H by 21.5" W by 16.5" D. Weight (shipping): 120 lbs. Question is whether there is an internal crossover (i.e., passive) inside to achieve the 80hz crossover point, or is it just a raw-driver-in-a-cabinet? Thanks!