Just a mad transmission line idea that i had for a pair of (shot) Focal Access 690CA1 or CA1690 6×9 speakers. It went well, although I feel with the Focal’s I could have achieved a response curve that could have dug deeper into the lower end. On the flip side, I tried another 1/4 wave transmission line enclosure with a pair of Alpine SPR-69. However all sis not go well. After contacting Alpine, The QTS for the SPR-69 speakers was too high for to be suitable for the transmission line enclosure I had in mind.