"speed" in bass has everything to do with the bass alignment of the box for a conventional speaker. A box with a low Qts will sound fast and tight with little boom or overhang (that goes for vented or sealed). A box with a high Qts will tend to sound fuller but also "slower". Box loading is generally considered optimal for a sealed design with a Qts = 0.7 but I found higher damping worked a bit better when I did a planar hybrid design (my bass box was sealed with a Qts of 0.6) and this sounded very "fast" and so matched sonically nicely with the planar driver (A BG radia). A lot of vented designs do not work very well for speed because they are having Q of 0.9 or greater. Horns are different and if designed well deliver a punchy dry bass that is pretty awesome and you are coupling with the air in ways a cone in a box cannot do. Sure the driver in the basshorn is a cone but it is the horn doing nearly all the work. In my Odeons, even with super heavy bass tracks (like from Interstellar soundtrack) the cone cannot really be observed to be moving significantly and yet bass is just pouring into the room. With a normal box speaker it would be pumping like hell. Distortion therefore is dramatically reduced with a properly designed horn because the driver itself barely moves. Planar speakers do not have a box so they have their own natural resonance, which can be quite high, that is offset by dipole cancellation and balancing this gives a better or worse bass depending on the design.
I used to have the Infinity IRS Beta, which has servo controlled woofers in a sealed box. The "brain" controlling this box had several adjustments (slope, shelving etc.) and one was Q adjustment. You could adjust the Q from 0.5 to well over 1. It was very instructional to see what electronic damping (through the feedback loop) would do to the speed of the bass. Interestingly, setting it at 0.5 resulted in an overly tight non-natural sounding bass that was little more than dull thuds. Loosening the Q towards the maximum resulted in a bloated bass that indeed sounded slow and smeared details from the planar panels. Ultimately, I found leaving it set right at 0.7 was optimal balance between control and natural decay of sounds. I took this knowledge forward later on with the Planar hybrid design.
I used to have the Infinity IRS Beta, which has servo controlled woofers in a sealed box. The "brain" controlling this box had several adjustments (slope, shelving etc.) and one was Q adjustment. You could adjust the Q from 0.5 to well over 1. It was very instructional to see what electronic damping (through the feedback loop) would do to the speed of the bass. Interestingly, setting it at 0.5 resulted in an overly tight non-natural sounding bass that was little more than dull thuds. Loosening the Q towards the maximum resulted in a bloated bass that indeed sounded slow and smeared details from the planar panels. Ultimately, I found leaving it set right at 0.7 was optimal balance between control and natural decay of sounds. I took this knowledge forward later on with the Planar hybrid design.