"Is the HD 660S2 worth the upgrade from the HD 650?"

"If you love the HD 650's sound signature and wish it had more sub-bass and less treble roll-off, yes — the HD 660S2 delivers both improvements. If you specifically love the HD 650's warmer, more intimate character, the 660S2 is slightly different rather than strictly better: it's more extended and a touch less warm."

"HD 660S2 vs HD 800S — which is the better Sennheiser?"

"The HD 800S is technically superior in every measurable way — wider soundstage, better imaging, more extended treble. But the HD 660S2 is more musically forgiving, more comfortable on average recordings, and costs less than half the price. For most listeners on a budget under $600, the HD 660S2 is the right choice."

"Does the HD 660S2 need a balanced amp?"

"No — the included balanced 4.4mm cable is a bonus, but the HD 660S2 sounds excellent on single-ended amplifiers. The balanced connection reduces noise at the floor and improves channel separation, but the sonic difference is subtle on most desktop amps."

"What amplifier pairs best with the HD 660S2?"

"The Schiit Asgard 3, FiiO K7, and JDS Labs Atom+ are all excellent pairings. For balanced output, the SMSL SH-9 or Topping A50s are good choices. As with all Sennheiser 300Ω headphones, tube amplifiers — especially OTL designs — offer exceptional synergy."

Sennheiser HD 660S2 Review (2026)

The Sennheiser HD 660S2 is the modern successor to the HD 650 — updated driver, improved bass extension, and better treble. Here's whether it's worth the premium over the classics.

What Does a Modern Sennheiser 6XX Sound Like?

The HD 600 and HD 650 defined what a reference open-back headphone should sound like for nearly three decades. Sennheiser’s 6XX series remained largely unchanged from 1997 (HD 600) and 2003 (HD 650) until relatively recently, with the HD 660S in 2017 and now the HD 660S2 in 2022. The question the audiophile community immediately asked: is the new model better, or just different?

Having spent time with all four headphones in the 6XX lineup, the honest answer is: the HD 660S2 is meaningfully better in two areas that matter — bass and treble extension — while maintaining the natural midrange that made the series legendary. It does not, however, render the HD 650 obsolete.

Design and Build

The HD 660S2 inherits the Sennheiser 6XX chassis with cosmetic refinements: a darker charcoal colour, slightly textured housing, and a more premium feel in the hand. The build is the same proven platform: velour ear pads, lightweight frame, dual-sided detachable cable with Sennheiser’s two-pin connector.

The notable addition is the included cable set: a standard 3.5mm terminated cable plus a 4.4mm balanced cable. This is a meaningful upgrade over the HD 650’s single-ended-only cable — it enables balanced connection out of the box for amplifiers with 4.4mm outputs. The cables feel higher quality than the HD 650’s stock cable as well.

Fit and comfort are identical to the HD 650: firm initial clamp, even pressure distribution, plush velour ear pads. Long-session listening is comfortable for most head shapes.

Sound Quality

Bass

This is the HD 660S2’s most significant improvement. Where the HD 650 rolls off below 40Hz, the HD 660S2 extends meaningfully deeper — sub-bass below 30Hz is audible and physical in a way that surprises listeners coming from the HD 650. Electronic music, film scores, and bass-forward rock benefit noticeably.

The mid-bass — which the HD 650 elevates for warmth — is slightly reduced in the HD 660S2. The result is a tighter, more controlled low end with better texture and less bloom. Whether this is an improvement depends on how much you valued the HD 650’s warmth: some find the HD 660S2 more accurate, others find it slightly leaner.

Midrange

The midrange remains the heart of the HD 660S2’s appeal. Natural timbre, organic vocal reproduction, acoustic instrument texture — the qualities that made the 6XX series beloved are all here. The character has shifted slightly toward neutral compared to the HD 650’s warmth, but it retains the musical, unfatiguing quality that distinguishes Sennheiser’s house sound.

Treble

The HD 660S2 directly addresses the HD 650’s veil. Treble extension is meaningfully improved — cymbal decay is longer, air and detail in the upper registers is more present, and the slight softness that characterised the HD 650’s top end is largely resolved. The result is closer to a modern neutral headphone without losing the smoothness that Sennheiser is known for.

This is not a bright headphone — the treble remains well-controlled and non-fatiguing. It is simply more extended and less rolled-off than the HD 650, which will satisfy listeners who found the HD 650 too dark.

Soundstage and Imaging

The HD 660S2 has a slightly more open, airier soundstage than the HD 650 — consistent with the improved treble extension and updated driver design. Imaging is precise, instrument placement is convincing on well-recorded material. Not as wide as the DT 990 Pro or HD 800S, but appropriate for the style of near-field presentation the 6XX series is known for.

Amplifier Pairing

The HD 660S2 is 300Ω and requires dedicated amplification. The same recommendations apply as for the HD 600 and HD 650:

JDS Labs Atom+ ($99) / Schiit Magni Heresy ($109): Excellent entry-level pairings — fully unlocks the headphone’s potential
Schiit Asgard 3 ($199): Preferred pairing — adds authority in the bass and detail in the midrange
Tube amplifiers: OTL tubes remain excellent with all 300Ω Sennheisers — the HD 660S2 is more resolving of upstream quality than the HD 650, so tube character is more apparent

Is It Worth the Price Over the HD 650?

The HD 650 trades for approximately $280–$330 new. The HD 660S2 trades for $499. The $170+ premium buys:

Better sub-bass extension
Less treble roll-off
A balanced cable in the box
Marginally updated driver and housing

If the HD 650’s rolled treble and limited sub-bass were specific frustrations for you, the HD 660S2 directly solves them. If you love the HD 650’s warm, dark, intimate character exactly as it is, the upgrade is less compelling.

Final Verdict

The HD 660S2 is the finest headphone in Sennheiser’s open-back lineup below $800. It takes the proven 6XX formula and adds the technical improvements the HD 650 was always missing. For a listener building a serious desktop system around a $199+ amplifier, it is worth the investment. For someone on a tighter budget, the HD 650 on the used market at $200 still competes seriously with the HD 660S2 at full price.

Sennheiser HD 660S2 Review (2026): The Modern 300Ω Upgrade