Sennheiser HD 660S2 Review

The Sennheiser HD 660S2 occupies a genuinely interesting position in the headphone world. It's not trying to reinvent anything — it's the methodical evolution of one of audio's most beloved lineages, the 600 series. And based on what the community has to say, that measured approach pays off in a very satisfying way.

The Sound: Familiar DNA, Meaningfully Improved

If you've spent any time with the HD 650 or the original 660S, the 660S2 will feel like coming home — but a home that's been tastefully renovated. The lower frequencies are the headline change. Where the older 600-series headphones could feel politely restrained in the bass, the 660S2 digs deeper and hits with more authority. One owner who compared it directly to sibling Sennheiser models described the bass as "tight and articulate," with real extension rather than a shelf drop that leaves you reaching for EQ.

The midrange is where Sennheiser has always won hearts, and the 660S2 doesn't disappoint. Users consistently describe it as natural, warm, and texturally rich — the kind of tuning that makes you want to replay albums you thought you knew. As one enthusiast put it after an extended listening session with the Avalanches' Since I Left You: the 660S2 "does a great job at fleshing everything out" without drawing attention to itself. That's exactly what a great transducer should do.

Treble is extended and detailed without tipping into fatigue — a balancing act that trips up a lot of headphones at this price point. Treble-sensitive listeners seem to breathe a sigh of relief here. It's airy enough to satisfy detail hunters but never harsh.

Comfort and Build: The 600 Series Formula

The chassis won't turn heads — it's the same familiar 600-series design that's been around for years. Whether you find that reassuring or boring probably depends on how long you've been in this hobby. Functionally, it works extremely well. The headphone is light, clamping force is modest without feeling insecure, and the ear pads are soft and roomy. Long listening sessions are genuinely comfortable, even for larger heads.

One direct comparison is telling: a user who owns both the HD 660S2 and the HiFiMAN HE400SE noted the Sennheiser is noticeably more comfortable despite the planars being lighter on paper. That's partly the clamping force, partly the padding quality — the 600-series headband and cup geometry have been refined over decades for a reason.

What's in the Box

Sennheiser keeps things clean and practical here. You get a 1.8m cable with a 3.5mm plug using the familiar twist-lock mechanism, a 3.5mm to 6.35mm screw-on adapter, and a soft drawstring pouch. It's not lavish, but everything you actually need is there. For those who need a balanced connection, an optional 4.4mm cable is available separately — worth knowing before you assume balanced is included.

Amping Requirements: Don't Skimp Here

The HD 660S2 is easier to drive than its older siblings — that was a deliberate design choice — but this is still not a headphone you plug into a phone and call it done. A decent DAC/amp pairing unlocks everything the tuning has to offer. The 660S2 rewards investment in your source chain. Budget a proper amp if you're buying this; it's not optional if you want to hear what it's actually capable of.

The Competition Conversation

At its price point, the HD 660S2 competes with planar magnetics from HiFiMAN and Audeze, as well as other dynamic driver flagships. Planars at this tier can offer a slightly wider, more spacious soundstage — the 600 series has always been known for an intimate, almost "in your head" presentation rather than a grand panoramic one. If expansive staging is your priority, that's worth factoring in. But for tonal accuracy, natural timbre, and the sheer pleasure of listening to music — not just analyzing it — the 660S2 makes a compelling case. The fact that one long-time Sennheiser owner who also runs an HD 600, HD 650, and HD 620S still keeps the 660S2 in regular rotation says something.

Who Should Buy the HD 660S2

This is a headphone for the patient listener. The person who sits down with an album and actually finishes it. The person who values tone and texture over spectacle. It's ideal for jazz, acoustic, vocal-forward music, and classical — genres where natural timbre matters more than slam or stage width. It's also a strong pick for mixing and critical listening where an honest, revealing but non-fatiguing response is exactly what you want.

If you're a basshead, a gaming enthusiast looking for wide virtual surround, or someone who primarily listens on the go without a proper amp — this isn't your headphone. But if you're building a serious desktop listening setup and want something that will still be making you happy five years from now, the 660S2 is hard to argue against.

Frequently Asked Questions

Q: Does the HD 660S2 need an amplifier?

A: Yes, strongly recommended. While it's more efficient than older 600-series models, it still benefits significantly from a dedicated DAC/amp to reach its full potential. Pairing it with a smartphone or laptop headphone jack will leave real performance on the table.

Q: How does the HD 660S2 compare to the HD 650?

A: The 660S2 extends lower in the bass with more impact and authority, while sharing the 650's celebrated midrange warmth. Treble is slightly more extended. Most users who own both consider the 660S2 a genuine step forward, especially for genres where bass presence matters.

Q: Is balanced cable included with the HD 660S2?

A: No. The box includes a standard 3.5mm cable with a 6.35mm adapter. A 4.4mm balanced cable is available as a separate optional accessory from Sennheiser.

Q: Is the HD 660S2 comfortable for long listening sessions?

A: Yes — this is one of its strongest points. The clamping force is light, the ear pads are soft and roomy, and the overall weight is low. Even users with larger heads report wearing them comfortably for extended periods.

Q: How does the HD 660S2 soundstage compare to planar magnetics?

A: Planars at this price tier generally offer a wider, more spacious soundstage. The 660S2 has a more intimate, precise presentation — excellent imaging but not an expansive panoramic sound. If big soundstage is a top priority, planars may suit you better.

— Tech Lead Editor, CPrice