I've known Sennheiser headphones for a long time. My first pair of studio 'phones was the HD 414 SL, a featherweight, open-back design that I still have 30 years later, albeit with new foam earpads. So it was with great interest that I read about the company's new flagship model, the HD 800.
Like the HD 414 SL, the HD 800 is an open-air design without sealed earcups. In addition, Sennheiser has retained its open-back philosophy, allowing the transducer's backwave to emanate into space unencumbered by an enclosure. This eliminates any interaction with the frontwave entering the ear, resulting in a clean, clear sound.
Acoustically, the earcups are designed to mimic the soundfield from two speakers by directing the waves to the ear at a 45-degree angle, much as sound from well-placed speakers would arrive. This is said to enhance the sense of spaciousness beyond that of most headphones.
The HD 800's other main technological innovation is its ring transducer. Measuring 56mm in diameter, the company claims it's the largest transducer to be found in today's dynamic headphones. The large surface area improves bass response, while the ring design mitigates the resonance problems in the high end that can occur with large diaphragms. The result is an impressive frequency response from 14Hz to 44kHz (-3dB).
As you would expect from a pair of headphones that lists for $1400, the HD 800 uses top-quality materials, including earpads made from Alcantara, a composite said to be particularly friendly to the skin and easy to clean. I've not heard this particular model, but if my experience with other Sennheiser headphones is any indication, the HD 800 should sound fantastic.