What's interesting about that list is how closely the max output curve for the DD18+ resembles the VTF15h in one port mode. Even the max long term output charts are very similar. I'd love to get these subs in a room and compare them qualitatively. The DD18 has less distortion, as you would expect, but the VTF15h looks like it does quite a bit better in the impulse response chart. I'd love to know what that all sounds like.