Sennheiser has always been known for exceptional sound quality in their headphone lineup, and now they’re expanding into new territory with the new over-ear HD 820 with a closed-back design. Open-air headphones usually produce the best sound, however by design, that openness allows in quite a bit of outside noise. The HD 820 is designed to create a sound that is similar to an open-air headphone, while providing some isolation from outside sounds. The HD 820 headphones have a frequency response of 12 Hz - 43,800 Hz (-3dB) with an impedance of 300 ohms.