1 Comment

Sound: *********
Value: *******
(Read about our ratings)

There is something appealing about big headphones. I think it’s the visual rebuttal of the endless trend towards smaller. True wireless earphones, wafer-thin flatscreen TVs, minimalist noise-canceling over-ears that are practically skeletal—most mainstream electronics just strive to minimize.

This makes sense. Most people don’t want to lug around or wear something particularly bulky. There’s also cost. Trim the bill of materials, and a company can cut the price or boost its margins.


So it’s nice to see Sennheiser’s HD 660S2 headphones, the latest in a long line of Sennheiser over-ears, be big and bold. Well, at least as bold as a pair of black-on-black headphones can be. Inside are 38mm drivers, which you can easily see thanks to the open mesh on each earcup. Despite their size, they weigh just 260gm, about the same as the Sony WH-1000XM5 headphones but less than most over-ear headphones I’ve reviewed recently. At $599.95 (all prices in USD), they’re a step up in price over most mainstream headphones, but not yet in the stratified realm of the ultra-high end. Potentially a sweet spot in performance that doesn’t completely break the bank.

In the box

In the box you get two sets of cables. One terminates in a 6.35mm (1/4″) unbalanced connector. The other terminates in a 4.4mm balanced connector. If you want to connect them to a source with the smaller 3.5mm headphone jack (a Sony NW-A306 for example), there’s an adapter included in the box. There’s also a storage pouch.


The 660S2s have a strong clamping force, though I imagine they’ll loosen up over time. The velour-feeling earpads are comfortable, if a little rough. Because of that roughness, combined with the clamping force, the 660S2s never really “disappeared” on my head the way I’d expected, given their light weight.


I was initially annoyed at how hidden the left and right labels were. They’re on the headband, in small type, tucked down practically behind the earpads. Only when I changed out the cables to try the balanced connection did I notice the tiny “L” and “R” where the cables attach to the earcups. Oops.


The overwhelming attribute of the 660S2s’ sound is size. They sound massive, with an enormous, open soundstage that’s paired with detailed and airy treble. While their soundstage doesn’t seem to extend quite as wide over the shoulders as some, the overall experience is one of space.

Take, for instance, the huge sound of “8” at the end of Sigur Rós’s new album, ÁTTA (24-bit/48kHz FLAC, BMG/Qobuz). Jónsi’s vocals soar over layers of strings, synths, delicate percussion, and other, almost whispered, voices. There was an openness to the 660S2s’ sound, both in terms of space/soundstage and atmosphere. They make grand music like this sound even grander. There was a clarity to the treble and midrange that was never harsh. I often talk about the difference between good bass and bad bass. The 660S2s are a great example of good treble that puts many headphones with bad treble to absolute shame.


A fairly iconic atmospheric sound is Phil Collins’s “In the Air Tonight” (Face Value, 24/96 FLAC, Rhino/Qobuz). It’s an absolute flood of that sweet, sweet, gated reverb, especially on the legendary drum solo that everyone knows how to play on their steering wheel. Through the 660S2s, the drums had a sharp attack and immediacy that didn’t quite attain planar-magnetic levels, but certainly got close.

Turning away from the processed 1980s sounds, I cued up Kirill Petrenko’s performance of Dmitri Shostakovich’s Symphony No. 10 with the Berlin Philharmonic Orchestra (24/96 FLAC, Berliner Philharmoniker Recordings / Qobuz). The instrument separation and clarity in the third movement, Allegretto, was fantastic. The delicate woodwinds never got overwhelmed by the brass and percussion, yet there was still enough bass to give this piece the scale and intensity it deserves.


Speaking of bass, a lot of Sennheiser’s marketing refers to “extended sub bass.” Chvrches’ “Asking for a Friend” (Screen Violence, 24/44.1 FLAC, Glassnote/Qobuz) certainly has enough bass to give that a test. Through the 660S2s, Lauren Mayberry’s transcendent soprano was front and center yet smooth, and the synth percussion sounds were present and assertive. The bass was down in the mix in the 660S2s compared to the treble, but it extended quite deep. It didn’t feel like the 660S2s lacked bass as much as they had a little additional treble, if that makes sense. They’d be good for someone who doesn’t avoid bass but prefers more treble.

For instance, with “Beach House” by Carly Rae Jepsen (The Loneliest Time, 24/48 FLAC, Silent Records IGA / Qobuz), the bass beat certainly had weight, but at a volume where I preferred the bass, there was too much treble for my tastes. As I’ve written before, I tend to like a bit more bass than most, but I think many would agree that these are a +1 or +2 treble on an imaginary EQ. That said, the treble is so good I don’t think I’d turn it down even if given the option. If that balance sounds like something you’d enjoy, you’d unquestionably enjoy these.


Most of my listening I did through my iFi Audio Hip-dac2, but to see how the 660S2s handled something less powerful, I listened to some tracks through my NW-A306 portable media player. The 660S2s sounded a little more constricted, but not overly so. An amp will get you the best sound out of these, but they’re easy enough to drive that you can still get great sound with a lower-power device. I even—gasp—plugged them into the headphone jack on my desktop. Again, using the amp was better, but they’ll still sound good if you want to use them away from your amp setup.


The Beyerdynamic T5p (3rd Gen) headphones are a worthy comparison, as they have a somewhat similar sound and are also light and comfortable. They were $1000 when they came out, but they’re available for around $800. Not an exact match for the 660S2, but certainly in the ballpark. With “The Story” from Brandi Carlile’s album of the same name (16/44.1 FLAC, Columbia/Qobuz), the 660S2s sounded more open, not surprising since they’re open-back. The Beyers had a bit more of a midrange push, with Carlile’s voice a little more forward. Cymbals were more present in the T5p headphones, which I didn’t particularly like. The Beyers had slightly more bass too, though the difference wasn’t huge.

The T5ps are excellent headphones, no question, and I found them more comfortable to wear. I’d say the 660S2s sound a bit more balanced, with a little more lifelike sound. I found them more relaxing to listen to, with slightly smoother treble. We’re talking very subtle degrees either way here. If someone told me they liked the T5p headphones more, I’d understand their point. However, with both of them sitting on my desk, I’d reach for the 660S2s to do some critical listening.

What about going the other way, price-wise? I recently reviewed the Sennheiser Momentum 4 and Sony WH-1000XM5 headphones ($350 and $400, respectively). Both are fairly “high-end” for their category, but add in features like Bluetooth and noise canceling instead of pure sound like the 660S2s. The Sonys were much darker than the 660S2s, more closed in and with far more bass. The Momentum 4s had some decent bass, and while their treble was more open than the Sonys’, they were practically muffled compared to the 660S2s.


The HD 660S2s sound fantastic. Full stop. I could nitpick here and there, but I think most people would love these headphones. My personal tastes tend to skew toward headphones with a bit more bass, so it might come as a surprise how much I liked these. Their clarity and openness are impressive in their own right, but having this airy of a sound while remaining easy to listen to is quite a feat. They almost totally lack any of the negative characteristics of treble-friendly headphones. The more I listened to them, the more I liked them. Vocals and acoustic instruments really let the HD 660S2s shine, but they’re neutral enough that they can handle just about anything.

. . . Geoffrey Morrison
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Associated Equipment

  • Portable media player: Sony NW-A306.
  • PC: iBuyPower Windows 10.
  • DAC/headphone amplifier: iFi Audio Hip-dac2

Sennheiser HD 660S2 Headphones
Price: $599.95.
Warranty: Two years.

Sennheiser Electronic Corporation
1 Enterprise Drive
Old Lyme, CT 06371
Phone: (800) 736-6434

Website: www.sennheiser.com

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  • This commment is unpublished.
    Ragav · 2 months ago
    Fantastic review! Could you also review the venerable Sennheiser HD 600 as also the HD 650, HD 560s, and the HD 599? I know Brent did a brief review of the HD 600 for the Wirecutter many years ago but still a detailed review is required. 

    Hope you accede to my request! 


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