The best placement is usually determined by trial-and-error and typically one shoots for the closest thing to a flat frequency reponse. Every room is different, so it's hard to guess where your best placement is. Typically, the sub will be placed close to a wall or sometimes near a corner. Again, trial-and-error. Try for not necessarily the loudest bass, but the most nautural sounding bass. Another type of placement is nearfield placementwhere the sub is put very close to the seating area.