https://www.cnet.com/news/sennheiser-goes-all-out-with-closed-back-version-of-high-end-hd-800s-ces/ >After essentially reinventing the luxury headphone market with the HD 800, where was Sennheiser to go next? I'll tell you: It came up with an even more indulgent set of cans the company is calling the HD 820. As the name suggests, the headphones are an updated, closed-back version of its statement piece. It's showing them off at CES here in Las Vegas this week. >How does Sennheiser get around the boxy sound of many closed-back headphones? With a piece of Gorilla Glass! The company says its curved "glass transducer cover" minimizes resonance and "ensures an incredibly realistic and natural sound field."