Yes, t-lines can be tailored to sound a certain way by using fibrous fillers such as wool and poly-fill, placed at certain spots down the line, to kill upper end peaks and control boominess(if needed). T-lines generally sound very nice. They can dig down low like a ported box, but group delay is lower than ported so the sub is more agile and can better handle quick transient passages(from what I have noticed). They'd be a lot more popular if they didn't take up so much space.