AKG K551SLV Closed-Back Reference-Class Headset with In-Line Microphone and Passive Noise Reduction, Black/Silver Powerful, 2-inch (50-millimeter) drivers deliver sound that's undistorted no matter how high you turn up the volume Real Image Engineering produces a huge soundstage and accurate sound quality The closed-back design helps prevent outside noise from entering your ears while also preventing the sounds you're listening to from leaking out The in-line microphone lets you make calls that are every bit as crisp and noise-free as the music you listen to on your smartphone The 2D fold-flat mechanism makes storing and transporting your headphones simple and worry-free