Three recent albums by blues duos show there’s strength in numbers. Singer-guitarist John Cephas and harmonica player Phil Wiggins play as one on Flip, Flop, & Fly, and it gives their effervescent folk-blues an easy intimacy. A similar musical combination can be heard on R&B, but singer- guitarist Roy Rogers and singer-harmonica player Norton Buffalo add a contemporary edge with angst-tinged lyrics and brisk-going-on-hyper playing. Singer Carol Fran and guitarist Clarence Hollimon strut from zydeco to punchy R&B to supper-club jazz on Soul Sensation! Fran’s brassy-yet-tender singing gets tasteful, intelligent support from Hollimon, who has enough range for half a dozen guitarists. Like any great partner, he’s willing to follow her anywhere. Flip, Flop, & Fly: A-; R&B: B+; Soul Sensation!: B+