Many of the Salk loudspeakers are transmission line...as are the new Philharmonic Audio towers.
https://www.salksound.com/type.php?format=Floorstanding
https://www.philharmonicaudio.com/Measurements-BMR-Tower.html
When executed properly, the bass will usually go pretty deep and with good tone.
Another advantage is the roll off is such that they are easy to blend with sealed subwoofers.