Slam means macro dynamics in the bass registers - at least in my book.
Walk into your local music shop and ask a salesperson to knock out four Beats on a kick drum. That's a good starting point to shoot for and can certainly be achieved in a good system without goosing FR. Good quality subwoofers (if crossed in high enough) are usually a good example. You're looking for high clean output capability between 50ish and 70ish hertz in most cases. Since most speakers don't spec this capability, you're mostly on your own in determining a full range speaker's ability to deliver "slam".
If you define the term more broadly (eg to include reproduction of a pipe organ) then the bass output capabilities must obviously extend well below the 50ish hz cited above. In all cases, you should be aware that many recordings - by design - will not provide the dynamics to allow full reproduction of bass macro dynamics.
Walk into your local music shop and ask a salesperson to knock out four Beats on a kick drum. That's a good starting point to shoot for and can certainly be achieved in a good system without goosing FR. Good quality subwoofers (if crossed in high enough) are usually a good example. You're looking for high clean output capability between 50ish and 70ish hertz in most cases. Since most speakers don't spec this capability, you're mostly on your own in determining a full range speaker's ability to deliver "slam".
If you define the term more broadly (eg to include reproduction of a pipe organ) then the bass output capabilities must obviously extend well below the 50ish hz cited above. In all cases, you should be aware that many recordings - by design - will not provide the dynamics to allow full reproduction of bass macro dynamics.