Most generic uprights of the 90's favoured slots cut with the speaker mounted behind, saving the need for an externally-mounted grill that could be smashed or poked at. Earlier cabinets may be different, as many early 'cabaret' style cabinets I played had speaker grilles. Doesn't really matter too much, as long as you test them first where you want to mount them for a good sound stage. Even some internally mounted speakers sound fine on some cabinets (notably self-enclosed PC speakers), as the acoustics of the cabinet space help amplify the sound.