I own the susvara and wonder exactly "slam" means according to all who speak of it
The way I see it, the “slam” one hears or feels in the lower frequencies, is associated with drums.
However, when headphones have this quality, you get an overall more tactile presentation
across frequencies. This impacts the bite of electric guitars, the snap of an upright bass guitar, the crash of cymbals, and so on.
A Focal Clear, for example, has more
so-called slam than an Arya or an Auteur, both of which I have enjoyed.
Currently, a hyothesis floating around, suggests that it comes down to driver excursion, amount of air being moved by the driver, etc., although
no standard measurements appear to exist.
It's not bass level, of course.
A Utopia doesn't exactly have a bass shelf but slams harder than headphones which have more bass on the FR.
Finally, a headphone like TC has both bass energy as well as this tactile presentation.