On the subject of BLHs. I designed and tested ( with excellent results) a method of wave cancellation for the problem of back wave reflections in filter chambers. So far i can have around 92% wave cancellation for frequencies above 480 hz. It was really very simple as the rear wave folds onto it self and the wave fronts meet at the rear of the driver and cancell themselves out. I will publish my findings after some " tweaking". ron