Overview

The Sennheiser HD 660S2 represents an intentional refinement within the legendary HD 600 chassis family. While its immediate predecessor, the original HD 660S, introduced a lower 150-ohm impedance, the S2 returns to the classic 300-ohm system architecture favored by desktop audiophiles. Beyond the impedance change, Sennheiser reworked the transducer surround and internal airflow to deliver stronger sub-bass extension without sacrificing the intimate midrange that made this line famous.

Now years into its lifecycle, the HD 660S2 has solidified its position as a go-to dynamic open-back headphone for stationary home listening, mixing, and audio mastering. Its success relies as much on its practical hardware engineering as it does on its acoustic tuning.

Design and build

Visually, the HD 660S2 retains the classic silhouette that Sennheiser has utilized for decades: a molded polymer frame, outer steel mesh grills, and plush velour earpads. Finished in a subtle matte dark charcoal with bronze-tinted branding, it strikes a understated, professional tone.

The real highlight of the HD 660S2 design is its entirely solderless, snap-together construction. There are virtually no glued-down structural components or hidden plastic clips meant to snap permanently into place. The headband, yolk assembly, driver capsules, and padding can all be disassembled with simple hand pressure or basic tools. Inputs are handled via Sennheiser's double-pronged proprietary 2-pin connectors located at the base of each earcup.

Everyday performance

Sound performance on the HD 660S2 stands out for its balance. The original HD 600 and HD 650 were often criticized for a roll-off in the sub-bass region. The HD 660S2 directly addresses this, yielding cleaner, more present sub-bass rumble without cluttering the lower midrange. Vocals retain their natural warmth, and high frequencies are smooth enough to prevent listening fatigue during multi-hour sessions.

Because of its 300-ohm load and lower sensitivity, plugging the HD 660S2 straight into a smartphone or base-level laptop output will yield weak dynamics and quiet volume. To experience what these headphones are capable of, pairing them with a dedicated desktop headphone amplifier or audio interface is essentially required.

Battery, durability, and longevity

As a fully passive dynamic headphone, the HD 660S2 carries no internal lithium-ion battery, Bluetooth radios, or active noise cancelling circuitry. This deliberate simplicity is its greatest strength when it comes to product lifespan. There are no software updates to brick the device and no chemical degradation to limit its functional life.

The mechanical architecture is remarkably resilient. The heavy-duty polymer headband tolerates considerable flexing, and the stainless steel adjustment sliders hold their position reliably. With basic care and occasional pad refreshes, an HD 660S2 frame can comfortably endure ten to fifteen years of daily desktop operation.

Common issues owners hit

Despite its stellar build quality, routine real-world use introduces predictable maintenance points on the HD 660S2:

• 2-Pin Socket Oxidation and Intermittency: The female socket contacts inside each earcup can stretch or tarnish over years of cable swaps, causing channel cutouts when the cable is bumped. Lightly cleaning or tensioning the internal pins usually resolves the issue.
• Diaphragm Buzz or Rattle: Because the outer back is protected only by open steel mesh, fine stray hairs or dust particles can work their way through and sit directly on the exposed transducer film. This creates an audible buzz or rattle on heavy bass notes. Gently opening the chassis to clear debris restores clean audio.
• Ear Pad Flattening: The velour earpads use high-density foam that compresses over 12 to 24 months of heavy daily wear. As the pads flatten, the drivers sit closer to your ears, which boosts mid-bass and reduces treble soundstage. Swapping in fresh factory pads resets the acoustic seal.

For step-by-step tear-down instructions and troubleshooting, check out our device hardware guides and specific Sennheiser HD 660S2 page.

Who it's for

The HD 660S2 is tailored for desktop audio enthusiasts, music lovers, and audio professionals who value sound balance, long-wear comfort, and equipment longevity. If you already own a dedicated headphone amplifier and want an open-back soundstage with punchier bass than vintage HD 600 models offer, this headphone hits the sweet spot. However, if you need mobile isolation, active noise cancellation, or wireless convenience, a closed-back Bluetooth model is a better fit.

Bottom line

The Sennheiser HD 660S2 is a triumph of iterative refinement. By marrying extended low-end response with Sennheiser's field-tested, fully modular frame, it delivers top-tier acoustic performance alongside near-unrivaled hardware repairability.

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