Though it only has three speaker drivers inside, that’s one more than many of the low-end Bluetooth audio systems we’ve tested, and SuperTooth’s design strategy here is sound: it divides 28 total watts of power between two 8-watt left and right drivers and a larger 12-watt “subwoofer” for bass. Control of the speakers is handled by a highly simplified control system on the face—a volume dial with separate track,…