He got a new sound system and he's been tweaking it. But the way his house is shaped and the way his set up is the bass carries all the way to the other side of my house.

What I ended up doing for right now is creating a "bass trap." I put my sub at the closest source of sound from him. And when I need to, I push high volume 55-75HZ to his house. It filters out much of his bass, but also sends noise back to his house to disrupt the flow.