Akon’s appeal is in the way he effortlessly straddles the worlds of saccharine R&B and hardcore hip-hop. For decades these areas were firmly segregated. Can you imagine Lionel Richie duetting with Run-DMC? Or Luther Vandross singing the hook on an LL Cool J track? Not only can Akon put a song like “Shake Down” (“Cause you will rarely find me / Without my weapon on me”) next to a song like “Never Took the Time” (“I can’t believe that your love is gone…why can’t you understand my pain?”) he is also an expert at wrapping extremely crude lyrics in sugar-coated melodies. His collaboration with Snoop Dogg, “I Wanna Love You,” has all the sincere yearning of a wedding vow, until you realize that Akon is singing about lusting for a stripper on a pole. But such is his charm. His voice has a candy clarity that is perfectly suited to the kind of delirious song epitomized by “Smack That.” At the same time, “Don’t Matter” displays a strikingly plainspoken voice and melodic sensibility (partly absorbed from the deep musical culture of his native Senegal) that make his songs hard to forget.