A 300-ohm open-back that re-engineers the HD 660S driver — impedance back to 300 Ω, resonance dropped to 70 Hz — to push the family's sound warmer and deeper. Sources agree on the broad strokes: a warm-neutral, relaxed, non-fatiguing tuning with smooth, silky treble, precise imaging, and the light, comfortable (if firmly clamping) repairable HD6xx build, plus deeper sub-bass extension than the HD 650 and 660S — though it still rolls off below ~40 Hz and is no one's idea of a 'bassy' headphone. Its arguments are the ones that define it: whether that new bass is a real, satisfying upgrade or a marginal, still-soft one; whether the pulled-back 3–5 kHz upper mids read as smooth and easy or scooped and 'muffled'; whether the stage is genuinely spacious or the same intimate HD6xx head-stage; and whether it's worth its price next to the far cheaper, near-identical HD 6XX, HD 650 and HD 58X. The split largely tracks whether you weigh owner enthusiasm or measurement-minded reviewers — and what you paid.
About this product
Open-back, 300 Ω — the 2023 successor to the HD 660S (whose impedance it raises back from 150 Ω to 300 Ω). Warmer and more sub-bass-extended than the neutral HD 600, less lush in the mids than the warm HD 650 and its cheaper Drop HD 6XX twin, and measures near-identically to the far cheaper HD 58X.
The HD 660S2 is Sennheiser's 2023 attempt to modernize its most storied lineage. It slots into the HD 580 / 600 / 650 / 660S family as the successor to the HD 660S — the same decades-old open-back chassis in a matte-black, rose-gold-lettered finish, but with a re-worked driver: the voice coil returns to the classic 300-ohm impedance and the resonant frequency drops from 110 Hz to 70 Hz, all in service of deeper, fuller bass than the famously bass-shy 6-series has ever offered.
That pitch — the beloved Sennheiser midrange plus more low end — is exactly what makes it polarizing. At its $599 launch it was panned for costing far more than the near-identical HD 6XX and HD 650, and a vocal camp of reviewers judged its pulled-back upper mids a step backward from the HD 600/650 magic. Owners, meanwhile, tend to love it — especially for modern, bass-forward music — a genuine 'don't trust the YouTube hype' divide. With street prices now well below MSRP, it's a warm, relaxed, easy-listening open-back whose worth depends heavily on which camp you sit in.
