When Teenage Engineering released its OP-1 portable synthesizer, in 2011, the device received glowing reviews from an array of audio authorities, including Nine Inch Nails frontman Trent Reznor and French composer Jean-Michel Jarre. A decade on, the Stockholm-based electronics maker aims for another hit with the new OB-4, a Bluetooth speaker system that it’s billing as a “magic radio.” The term isn’t too far off: The mobile, four-speaker hi-fi memorizes everything it plays, allowing users to rewind, stretch, or loop any track that was pumped through it in the previous two hours—regardless of whether the tunes came from live radio, a streaming service, or a plugged-in instrument. Its handle houses a spiral antenna and turns into a stand, which positions the gadget’s top at an angle to provide easy access to its dials and buttons. There’s also a feature called “disk mode,” in which three recordings—“ambient” (a low-pitched drone), “metronome” (monotonous ticks) and “karma” (chanting)—can be used to facilitate focus or relaxation. With a lithium polymer battery that lasts for eight hours when played at its loudest (or for 40 hours at average volume), the souped-up speaker ensures that there’s plenty of time to take in its sounds.