HD671 is an automatically adjustable headset with a 50mm moving coil single enclosed structure, simple and stylish design, elegant appearance. At the same time, it has the inherent characteristics of light weight, low impedance, superior sound quality, and good sound quality even when connected to a mobile phone! The HD671 is the world's lightest full earmuff closed earphone. And the soft composite material earmuffs are comfortable to wear and soundproof, and beyond the imagination.