The Philips Fidelio X2 open-back headphones retain their popular predecessor’s solid aluminum construction, long-wearing comfort, and smooth, spacious sound—with a few notable improvements. The new drivers use the multilayered diaphragm technology first seen in the brand’s S2 IEMs, designed to deliver cleaner treble and more accurate bass. The 3.5-millimeter jack is a change from the X1, too, though a 6.3-millimeter adapter is included.