Bulletin Today | LegacyIf you grew up in the 1960s, when you think of R&B, you probably think of classic Motown — the earnest, energetic sound of Smokey Robinson, Marvin Gaye, and the Temptations, among others — or else the harder, funkier Stax/Volt Records sound from Memphis, exemplified by the Staple Singers and Isaac Hayes. But if you were a teenager a decade later in the mid-1970s, you probably got down at high school dances to what people called the Philadelphia Sound or …