It is quite difficult to find a high-power, high-quality 8-inch subwoofer. You just found the only one that I could find after searching extensively.
The 18 Sound 8NW650 is a 8 inch neodymium woofer developed in response to a specific market requirement for a light weight design that combines excellent linearity with high power handling capabilities.
18 Sound 8NW650 Subwoofer Specifications:
Nominal Power Handling (RMS): 300W
Continuous Power Handling (RMS): 600W
Freq Range: 55-6300 Hz
Sensitivity: 96.0 dB
Net Weight: 2.4 kg (5.29 lb)
Voice Coil Diameter: 65 mm (2.5 in) Ø edgewound aluminum wire, wound on a high strength fiberglass former
The voice coil is cooled through airways placed between the chassis back plate and the magnet faceplate and carefully designed ventilation ducts made into the metal back plate.
An exclusively-developed membrane treatment has been applied, which renders the cone humidity repellent while not increasing the total moving speaker mass, giving the woofer the ability to perform well in humid environments.
A special epoxy treatment is applied to the top and back plates making the woofer far more resistant to the corrosive effects of salts and oxidization.