https://www.theverge.com/2018/1/8/16858130/sennheiser-hd-820-headphones-price-release-date-ces-2018

When friends ask me about my endgame headphones — the ones that I would buy, love, and cherish above all others — my answer is usually the Sennheiser HD 800 S, a pair that I reviewed back in 2016. I’m not alone in my admiration for Sennheiser’s pricey flagship cans, and I suspect I won’t be alone in my profound excitement and curiosity about a new Sennheiser HD 820 that the German audio company just announced at CES.

The 820 is a closed-back variant of the 800 S, adding a measure of isolation between your music and the surrounding environment. The original 800 S is like a sieve when it comes to letting outside sound in, and it pushes almost as much volume out of the headphones’ sides as it does into your cranium. There’s good reason, however, for this antisocial open-back design. Closing off the acoustic chamber around your ear complicates a headphone’s design and threatens the purity of its sound by creating undesirable resonances and reverberations. That’s why we usually see open-back headphones like the 800 S or the Focal Utopia competing for the title of having the best and most pristine sound.