Alright, so maybe we're talking about different things when it comes to slam. For me, it's about when a solid bass note comes out of nowhere and you can both hear and feel it in a gutteral way. In my experience, it takes removing room resonance, electronic overhang, and noise out of the equation for those bass frequencies to be fully resolved and to have the fullest aesthetic impact. However, I also acknowledge that you can get there by leveraging uneven bass response in speakers, untreated room loading, and other "inaccurate" characteristics to make bass kick pretty hard. But in this case, you'll be trading in many other important aspects of the sound in order to maximize that bass impact.
Like others have mentioned, speaker design will play a big part. Ported speakers in general will "bump" more than other designs due to the resonant frequency of the port emphasizing at that frequency. It's not a completely even response, but it does give you that sense of drive and bass dynamics. That can be pretty fun if done well.
