Sennheiser HD 660S2 headphones offer more high-end low end
The German audiophile brand wants personal audio enthusiasts to warm up to a retooled, bass-reinforced model in its reference line.
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Audiophiles are consistently desperate for something new … yet somehow constantly afraid of change. They can be relied upon to lament a headphone’s shortcomings, however minor, then be skeptical when a new model is announced. If that sounds exhausting, it is. Consensus is not a state typically found in these circles. The Sennheiser HD 600 family of open-back reference-level headphones, however, is legendary, and few would argue. Introduced in 1997, the HD 600 established itself as an icon of clinical, crystalline monitoring. In 2003, the HD 650 joined the party, bringing the epitome of smooth musicality. In 2018, Massdrop (now Drop) launched the HD 6XX collaboration, a variant of the HD 650 available for $239 (making it one of the best values in audiophile headphones on the market). Around the same time, the HD 660S retuned performance with precise mids even more nestled in the silky spectrum. This brings us to the new news: The HD 660S2, a revision that promises to address common feedback—not enough hefty bass—though low-distortion low end comes at a higher premium.
The HD 660S2 shares the lightweight plastic body of the line, complete with instantly recognizable steel-mesh grilles that let you peer in at the tweaked transducers and admire their airflow. The velour-wrapped foam earpads/headband also remain the same, clamping these jet-black ovals (with their bronze accents) firmly to your head for comfort and clarity. Like all the 600 series, the HD 660S2 offers zero isolation and high leakage, so only consider them if you have a quiet listening station. Presumably, the lush mids remain intact—good news for fans of vocal-rich material.
What has changed in the 660S2 are the impedance (now 300 ohms, vs. 150 ohms for the original) and the voice coil and surround (lighter, lither)—meaning higher magnetic force, heightened speed, a blacker backdrop, and lower resonant frequency. Punchier sub-bass should now extend to 70 Hz (formerly 110 Hz), while grain is said to be reduced between the treble peaks. Another thing the 660S2 achieves: an increased price tag of $599.95.
The approach with Sennheiser’s HD 600 family has always been equals not sequels—no one model is the best, but one can be the best for you. Now, with the HD 660S2, a warmer, smoother, but still natural response could be kicking—provided you have an appropriately powerful, precise signal chain (think accuracy-focused DACs, headphone amps, and/or DAPs, particularly ones with a 4.4mm balanced port).
Preorders for the Sennheiser HD 660S2 are open, with headphones scheduled to ship Feb. 21. We’re getting a pair in the coming weeks, so check back for our deep dive into this hi-fi headphone’s dramatic depths.