Open-back over-ear headphones
Sennheiser's update to the HD 660S: an open-back HD 600-series headphone with a warmer tuning and deeper sub-bass, made for long, relaxed listening sessions.
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Extended sub-bass
A revised driver surround lowers the resonant frequency from the HD 660S's 110 Hz to 70 Hz, for more output in the lowest octaves. Most reviewers found the bass reaches deeper than on earlier HD 600-series models, though it is still not a bass-heavy headphone.
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Warm, relaxed tuning
It is tuned warmer, with smoother treble, than the HD 660S. Reviewers found it relaxed for long listening, but the laid-back midrange can make dense mixes sound less clear.
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Balanced cable included
Two detachable 1.8 m cables are included: one with a 6.35 mm plug and a 3.5 mm adapter, and one with a 4.4 mm balanced plug.