Yank
Bulbous Also Tapered
I'll explain. In the Harbeth m40 speakers, the midrange is reproduced by an eight-inch Radial driver, it's in the middle between the tweeter and the bass driver. This Radial driver inside the cabinet has its own volume. That is, there is a small box attached to the front of the enclosure from the inside, in which the midrange Radial driver runs. You can see pictures of how this is set up in various reviews on the Harbeth m40. The rest of the cabinet is for the bass 12" driver. It needs a lot of volume and is slow. And the midrange Radial driver is fast. And it turns out that the midrange in the Harbeth m40 is faster than in the Harbeth shl5plus, where the Radial driver has to play both midrange and bass, so it runs the entire volume of the speaker cabinet.
When fed by a 400Hz low-pass filter, how "fast" does a woofer need to be?