The UK grime group Da Black Op’s has one mission: To destroy your eardrums with pummeling sub-bass. Their Bandcamp is full of heavy productions primed to rattle speakers and scare off birds. Dropped without warning a few days ago, “GRAVE YARD,” a demented rattler from the group’s leader (and label head) Jon E Cash is as haunting and sinister as its title. Like the first act of a horror flick, it starts out unassuming: Bells ring in the distance, a moan repeats, airplanes zoom overhead. When the bass finally appears, you are transported into the lower depths. It’s a dark nocturnal hum that does not let up, a woozy assault on the senses prolonged by weary percussion and the howling of wolves. Jon E Cash has been making music like this since the early 2000s; he calls it sublow, which seems apt. Each minute digs you another foot under.