Danny, what will the increase in output be when a third GR12-16 is added to the usual two in a pair of H-Frame OB subs? Have you built a pair of three-driver H-Frame subs, or heard a pair built by someone else? Do you consider the increase in output justifies the $400 it takes to add the third pair of drivers? They would be mated to a very output-challenged pair of ESL's set-up in a 10' X 13' X 19' room, playing mostly acoustic music at room filling volume.