SubTerrain™ underground subwoofer, 12' Driver, 400 watts, 4Ω/70V switchable. Sold each. TruAudio’s SubTerrain subwoofers are designed to do exactly what its name intends - Be buried in the ground. This form factor allows for the outdoor listening experience to now include deep hearty bass while effortlessly blending into any landscape. Tech Tip: Before burying the sub, put gravel at the bottom of the hole for drainage, leveling and to help prevent freezing.