[ORIGINAL MSRP $599.99, currently $479.99 from Sennheiser in November 2025 and similarly priced at Amazon.1 Purchased (lightly?) used from Hawthorne Stereo for $250 in October 2025.]
[Tl;dr: The Sennheiser HD 660S2 is a worthy addition to the 6X0 family, slotting in somewhere between the HD 6XX and the HD 600. To me they’re pretty similar to the 6XX, which unfortunately makes them a challenging value proposition as they’re more than twice as expensive. And that’s kind of the overall story of this headphone; it’s a really great headphone at a not-so-great price point, and if Sennheiser would get a little more aggressive about its pricing, I could wholeheartedly recommend it. Unfortunately, Sennheiser seems slow to let the prices come down with this particular model, and has recently undercut it with the really excellent HD 490 Pro release.
For the moment, if you can get it used for less than $300, it’s a great deal. At MSRP, it’s not my first choice (and especially not in the US, where you can currently order an HD 6XX for $179 from Drop2).]
Cost-agnostic: 7 out of 10 Denalis
Cost-sensitive: 5 out of 10 Denalis
TABLE OF CONTENTS:
- Introduction
- Review notes
- The Basics
- Sound
- Amplifier Compatibility
- Build Quality & Appearance
- Value & Comparisons
- Overall
Introduction
I’ve been on a bit of a tear the last few months reviewing the various Sennheiser 600 series headphones, and today I have the most recent addition to the official 600 series: the Sennheiser 660S2! I think this will complete the existing family, though I also have in for review a pair of Sennheiser HD 490 Pro, a headphone that I would consider an unofficial member of this family more than a member of the 500 series.
As I noted in my review of the Sennheiser x Massdrop HD 58X, I’ve long been a fan of this line of headphones. My first headphone, period, was an old Sennheiser 500 series, and then my first serious, audiophile headphone was the excellent Sennheiser x Massdrop HD 6XX, which I still listen to regularly seven years later. I mostly unplugged from the series after that for awhile, until I found a good deal on the classic HD 600, and then had an opportunity to borrow an HD 660S and an HD 58X. I wasn’t the biggest fan of the 660S, but heard really good things about the 660S2 and I was curious to try them out. I made Hawthorne Stereo a reasonable offer on a lightly used pair of the 660S2, and they accepted it! It was a little lower down my stack of things to review, but I happen to still have the borrowed HD 660S in my house and I wanted to do some direct comparisons before I return them.
Review notes
Terminology
I’m going to be referring to the HD 600/6XX/650 family a lot in this review, and I will refer to them collectively as the 6X0. I’ll also include the HD 58X Jubilee (as an homage to the first 600 series, the HD 580) and the HD 660S/660S2 in that family as they’re both attempts to address perceived shortcomings in the HD 650.
Testing rig
Based on my philosophy on the allocation of resources in headfi, except where otherwise noted I’m going to primarily be testing these with a Schiit Modius/Magnius6 stack, running balanced via a Hart interconnect and connected via USB-C to a custom gaming PC running the Roon client.7
EQ
As noted in the Bathys review, I mostly prefer to test headphones with their default tuning, assuming that most people won’t take the time or make the effort necessary to use a third-party EQ. And the 6X0 family really doesn’t need EQ; they mostly sound pretty good to me out of the box.
EQ Update
[EQ Update: These really don’t require any EQ. I fiddled around with a couple of profiles and ended up preferring the box tune. At most, I have added a slight bass shelf (though it hardly needs it):
]
Volume
Here are the volume settings I use with the Sennheiser HD 660S2 (unless otherwise noted, running via Roon with no headroom management, playing Daft Punk’s “Face to Face” from Tidal):
- Mimir/Jotunheim 2 (Mimir has a -15 dB pregain applied via Forkbeard): low gain, 12:00 (balanced); low gain, 1:30 (single-ended)
- Modius/Magnius: low gain, 10:30 (balanced); low gain, 11:30 (single-ended)
- Modi/Magni: low gain, 9:00
- Fulla: 10:30
- Hel2: 8:45
- E30/L30: lowest gain, 11:00
- Chord Mojo: white, light red, light red, red3
- North American Apple dongle via iPhone 15: 60%
- Apple dongle via Mac Studio: 40%
My testing method/philosophy.
My torture testing list: Apple, Tidal, Spotify.]
The Basics
Before there was an HD 660S2, there was an HD 660S. Before the HD 660S, an HD 6XX. Before the HD 6XX, an HD 650. Before the HD 650, an HD 600. And before the HD 600, the legendary HD 580 Precision (and in the interim, the original HD 580 Jubilee). Since the introduction of the HD 600 in 1997, Sennheiser has been regularly tweaking the frequency response and releasing new models, mostly increasing bass and reducing treble, and leaving the physical form pretty consistent and recognizable. The HD 660S2 is the most recent entry in the official 600 series, with a debut in February of 2023 (though I could, and might, argue that the HD 490 Pro is more properly considered in the context of the 600 series within Sennheiser’s lineup).
The HD 660S2 is a passive, open-backed headphone weighing in at fairly light 260 grams, identical to the rest of the 6X0s. In terms of drivability, they’re a throwback to the 6XX and 600, with an impedance of 300 Ohms and a sound pressure level (SPL) of 104 dB/Vrms after Sennheiser tried a lower impedance of 150 Ohms with the 660S. It’s primarily built out of plastic with nice velour pads like the rest of the 6X0s, and it appears that most of the parts are interchangeable with the 6X0 as well. This means it also has a pretty robust market for third-party parts, including pads.
Sound
Like most of the 6X0 line, the 660S2 is a headphone that really excels at both quiet, sparse tracks and reproducing silence, but still does a good job with even crowded, intense tracks like “Face to Face” or “Easy.” It’s a very specific tune (strong mids, less bass, minimal sub bass, and relaxed treble), but it’s a really good example of that tune much like its sibling the HD 6XX.
The soundstage is pretty normal for a 6X0; it’s relatively intimate and close-in to your head, though you do get some separation among instruments within that relatively narrow sound stage. On a track like “Chan Chan” the bass and the guitar in the left track sound like they’re very close together, whereas on some headphones, particularly good planars (see, e.g. the Hifiman HE6se v.2) you have a soundstage that feels fifteen or twenty feet across. You still get good layer separation; though instruments sound like they are very close they’re still distinct. Interestingly, at least some instruments occasionally feel like they’re behind you. For example, on “Love Can Damage Your Health (Laid Mix)”, the panning/rotating guitar riff at the beginning really feels to me like the guitarist is walking back and forth behind me rather than level or in front of me. Very little rotational soundstage either as a result. The channel separation is clear and distinct, and not as distracting on the 660S2 as it can be on other headphones.
The dynamics are good. Starting “It’s All So Incredibly Loud” at a reasonable volume at the beginning gets unbearably loud by the end (I found myself turning it down around the three minute mark, even before the final crescendo). The microdynamics are fine but not remarkable; the low bell tones on “Angel (Blur Remix)” are solid but don’t have quite the bite that I want (and they don’t have the slight warble before settling into the tone that I get from the best headphones), but the treble bell tones are nicely crispy and punchy. The same is true on “Intro”; the brass fanfares are nicely accented, as are kick drums, but I don’t get quite the same punch on most of the bass.
Overall, I certainly enjoy the detail and resolution and would put it roughly on par with the rest of the 6X0 family. I don’t have a great metric for testing this, but anecdotally I’d put it right around the 6XX and maybe a hair behind the 600 for pure detail. You don’t quite hear Meshelle Ndegeocello’s fingers coming up off the strings at the beginning of “What Did I Do?”, but you can hear them sliding around on the strings, and the silences between notes are clear, clean, and crisp.
I personally really enjoy the bass from the 660S2; it’s a pretty typical member of the 6X0 family in that it doesn’t have a huge amount of bass quantity, but does have a great bass quality. The bass is generally very clean and precise, if not overly present or powerful. It’s one of the best reproductions of the bass line at 2:50 on “Out of My Hands,” slipping in nicely and then moving forward in the mix. It does a surprisingly good job with the intense bass on “Superpredators,” though it does get a little splattery at times (like most headphones). You do lose some of the sub bass like you do with most Sennheisers, but I honestly don’t listen to that much music that uses those frequencies and you still get a satisfying brain wobble on a track like “Limit to Your Love” even if the lowest notes around 2:20 start to audibly roll off.
The midrange on the 600S2 is classic Sennheiser, which is to say a real strength. Timbre is generally correct, with the two guitars in the middle of “Garcia Counterpoint” clearly identifiable by tone, not just placement in space. Most guitars, male and female vocals, etc. are beautifully reproduced and stand out in the mix without being overdone. Jill Scott’s voice carries through on “Calls”, even when the mix starts getting busy around the three minute mark. You even get a really nice clarity on the background vocal riffs, which can disappear on some headphones. Justin Hicks’ voice is a little de-centered at the beginning of “What Did I Do?” but that’s really an artifact of the mix and he carries through nicely starting around :55 when his relative volume increases. Johnny Cash’s voice on “Hurt” is perfectly reproduced, even where the recording gets a little too hot towards the end.
The treble is solid, but not exceptional (typical for the 6X0) line. It’s a little rolled off compared to a neutrally tuned headphone (or even something like the 6XX), but still provides the sense of clarity and detail I want for most of my listening. The guitars on “2021” stay this side of sharp, and Miles’ solo on “Will O’ the Wisp” is perhaps a smidge recessed compared to what I might prefer but is still perfectly acceptable.
Amplifier Compatibility
Like the rest of the 6X0s, the HD 660S2 aren’t super sensitive to amplifiers but do benefit from running off of an amp with decent power output. They’re also able to scale pretty well; while they do well with something like a Schiit Modi/Magni stack, they also sound really good from something like the Mimir/Jotunheim stack or a Chord Mojo 2. And as a high impedance headphone, they do seem to benefit (to my ears at least) from a tube amp like the Apos Gremlin.
Build Quality & Appearance
The HD 660S2 is pretty similar to the rest of the 6X0, but it’s been awhile since I did a full, end-to-end review of the build quality of a 6X0 and my review style has changed a bit, so I’m going to do it for realsies this time instead of just linking to an old post.
Connectivity
Like all of the 6X0s, use Sennheiser’s nonsense split, two pin style connectors, and ship with a distinctly underwhelming rubberized OEM cable. Unlike most of the 6X0s, at least the 660S2 comes with both single ended (3.5 mm w/6.35 mm adapter) and balanced (4.4 mm Pentaconn) cables, both around 6 feet long.
I really, really don’t like Sennheiser’s OEM cable (though they’re a damn sight better than Focal or Hifiman’s higher end line), but I lived with the 6XX’s cable for almost seven years just fine. I’ve since upgraded to Hart interconnects (and I’ll probably snag a couple more if I keep these), but they’re perfectly fine and competent cables.
Construction
Like the rest of the 6X0 family, the Sennheiser HD 660S2 is mostly plastic and some metal (the interior of the band, the grills, etc.). They’re very light at only 260 g, but in line with the rest of the 6X0s.
Because of the construction and weight, they feel remarkably cheap at first, though solid, and I have used and abused my 6XX for most of a decade with them still fully functional (if slightly dented in one of the grills from an enthusiastic golden tail catching a cable). The plastic frame attached to the slim metal band gives it very little in terms of rotation. Overall, I would say the cups rotate maybe 30 degrees, and tilt maybe 30 or 35 degrees; most of the flex in the 660S2 comes from the headband. Each temple does extend approximately 3″, accommodating a lot of head sizes, but they’re definitely less adjustable than many other headphones in this space.
Comfort
Back when I did my 6XX review in January, I stuck with the simple “They’re pretty comfortable.” At this point I have a more nuanced view. The weirdest part about doing A/B’ing with the 6X0s is how acutely aware you become of their clamping force after spending time with something like the HD 490 Pro. I never thought of the 6XX as being particularly clampy, but after an hour wearing the HD 490 Pro, even my seven year old, heavily-loved 6XX feel like very clampy bois. Weirdly, I’m usually a fan of clamping force as a way to help distribute weight more evenly between the top of the head and the sides, but the 6X0 are so light that I could really do with a little less clamping. Speaking of weight, there could be a little more padding on the top of the headband, but I personally don’t have a problem with that given how light the headphones overall.
I still stand by the 6X0s being comfortable, and more so when you aren’t wearing glasses. But, if I were wearing a pair of headphones for hours on end instead of intermittently (or swapping frequently like I do for testing), at 43 years of age I might choose something other than a 6X0. Which is an interesting development, and might change the way I feel about some of the comparisons below.
Appearance
Honestly, I think the HD 660S2 is the most attractive of the 6X0s. The differences are pretty minimal, but I really like the copper-on-black colorway they went with for this release, as opposed to the white-on-black for the 660S, blue on black for the HD 600 (or god forbid, blue on marble that they did for that special release), or white-on-black for the 6XX.
The differences in appearance are minimal, but I like the 660S2’s choices. And we, after all, listen with our eyes at some point.
Value & Comparisons
This is a pretty crowded field in my collection; even just looking at Sennheisers, its a reasonable comparison to the 600, 6XX, 58X, 660S, and 490 Pro, and the premium pricing makes it a reasonable comparison to things like the Focal Elex/Clear, Hifiman Arya Stealth/HE6se v2, and Meze 105 AER/109 Pro. For convenience, I’m going to group these a bit.
HD 6XX/600/58X/660S
[Caveat: the biggest challenge with testing 6X0s is that these headphones are particularly sensitive to pad wear. I don’t know much about the provenance of this pair of 660S2, but they appear to be pretty lightly used and the earpads are still relatively firm so I’m guessing they haven’t seen a ton of wear. The rest of the 6X0s I’ve tested have used relatively fresh pads with the exception of the OG 660S, and they’re not particularly heavily used. Overall, I’m reasonably confident that I’m comparing apples to apples.]
Overall, the 660S2 are a great entry in the 6X0 line, though they might benefit from a slightly more aggressive pricing decision. If you don’t consider cost, they’re mostly pretty competitive.
I’ll start by dispensing with the easiest comparison here: it’s rare in this market that one product universally, objectively beats another, but this is one of those rare cases; the 660S2 is an unambiguous improvement over the original 660S in virtually every way, and the few places where it’s not unambiguously, objectively better, it’s not any worse (comfort, for example). This is a substantial upgrade over the 660S in almost every way, and you should 100% not buy the 660S over the 660S2 unless it’s WILDLY cheaper (as in, new in box cheaper than the price of a new 6XX).
Next, my favorite of the bunch, the HD 6XX.8 I’m honestly not sure if I could tell the difference in a true blind test. Even knowing which is which (Editor’s note: and even after reviewing the graphs after completing this section), maybe the bass is a hair stronger on the 660S2 but slightly cleaner/more crisp on my old 6XX? But that could be a volume variation.9 In some ways, this is actually a ringing endorsement; I really, truly love the 6XX and a favorable comparison to them is pretty great … until you take into account the pricing differential. The 6XX is, at worst, $199, and often on sale for more like $179. The 660S2 is around $350 renewed, more like $430 new. Even if the slightly enhanced bass I’m hearing is real and not just placebo, it’s not worth almost twice as much (renewed) or more than twice as much (new), and I’m picking the 6XX every time. Even for the $250 I paid for these used, I genuinely think I’m choosing the new 6XX every time unless I’m doing something where I care about the slightly more attractive appearance.10 If they were the same price, would I take the 660s2? Maybe? They’re pretty equivalent to my ears, and you could reasonably go either way.
Just for verification, let’s look at some graphs, this time from listener:
This seems about right? There’s a marginally better bass response, particularly in the sub bass, but neither are particularly strong in that region. I’m a little intrigued by the mids, where the 660S2 are slightly stronger on the low end before swapping for the upper end, but the differences aren’t huge (and for whatever reason, I don’t hear the spike listener measures in the 6XX’s treble around 16 kHz). Overall they’re pretty similarly tuned headphones, and this more or less aligns with my lived experience. Nothing convinces me that it’s worth paying twice as much for the 660S2 over the 6XX.
As for the 600, I’ve been pretty clear that while I prefer the 6XX’s over all tune, the 600 has a specific place in my collection because of it’s even more emphasized mids and slightly more detailed treble. I don’t think the 660S2 displaces the 600’s role for me in listening to jazz and more vocally-focused tracks, though I would prefer its tuning for most of the music I listen to (just like the 6XX). So, in a vacuum, if I had to pick one of these headphones, it would be the HD 660S2. However, in the real world, when we add in price considerations ($489 for the 660S2 and $290 for the 600 in November 2025), the 600 is the clear winner. Graphs:
Yeah; the strengths of the 600 (particularly over the 6XX/650) is in the mids and treble, and this makes a lot of sense.
Because I do prefer the 6XX’s tune over the 58X’s, and the 660S2 is pretty equivalent to the 6XX, I think11 I’d end up preferring the sound of the 660S2 over the 58X, but when we take price into account (the 58X consistently retails around $200), I’d be pretty hard pressed to pick the 660S2 at more than twice the price. I jokingly call the 58X a more 6XX-y 6XX, and you could argue that the 660S2 is a more 58X-y 58X with a bumped bass and reduced treble.
In sum, here’s my current order for the 6X0s in November 2025:
- Price-agnostic: HD 6XX/650 = HD 660S2 > HD 60012 > HD 58X > HD 660S
- Price-sensitive: HD 6XX > HD 600 > HD 58X > HD 660S2 > HD 650 > HD 660S.
Sennheiser HD 490 Pro
For me, the most interesting Sennheiser match up coming in was the Sennheiser HD 490 Pro, another new member of my headphone collection that I’ve been listening to a lot and plan on reviewing in the near future, and which retails around $350 for the regular Pro version, and $400 for the Pro Plus version.13 I haven’t done all of my testing, but my general impression at this point is that while I slightly prefer the tuning of the 660S2 (and most of the rest of the 6X0s), the 490 has a lot of advantages overall. One thing that I’ll get into when I get around to my review of the 490 Pro is that it comes with two sets of pads: 1) the velour “producer” pads (with a more v-shaped presentation) and 2) the fabric “mixer” pads (with a more neutral presentation). I’m still figuring out what I think about these headphones, but I’ve mostly been listening with the velour pads so that’s the primary comparison here.
The bass on the 490 is certainly stronger than that of the 660S2, and I find myself depressingly close to saying that it’s also clearer.14 It’s not that the bass is bad on the 660S2; quite to the contrary, I really enjoy its presentation but there is decidedly more punch on the 490 on tracks like “I Against I”, and when Edgar Meyer hits the lowest note on “1B”, the resonance is substantially richer and warmer. The microdynamics are also just better on the low end; the low bell tones on “Angel (Blur Remix)” hit slightly harder though they still lack the wavering tone before settling that I want out of the best headphones. The 660S2 is not without its upside, though, as I think the bass is crisper (notes end when they should where they might linger a little with the 490), contributing to the 660S2’s better sense of silence. And the bass on the 490 Pro can be a little bit overwhelming on tracks like “Limit to Your Love”, though even when it makes my brain throb it’s still pretty well controlled and defined.
I prefer the vocals on the 490 Pro, particularly male vocals, where they feel much more present and forward than on the 660S2. Justin Hicks is singing right in front of us on “What Did I Do?” on the 490, whereas he feels slightly recessed on the 660S2. It’s less pronounced with female vocals to my ears, with Christine Hoberg sounding nearly identical across the two on “Clair De Lune,” and there are tracks (particularly sparser ones) where I may prefer the vocal performance of the 660S2. Same across the rest of the mids; I think the 660S2 have slightly better timbre (particularly for the guitars on “Garcia Counterpoint”) but it’s not entirely consistent from track to track.
The treble performance of the two is also pretty similar, with maybe a slightly increased tendency towards harshness from the 660S2, though neither is particularly spicy in the treble, and there are tracks like “Will O’ the Wisp” where I may actually prefer a little extra sharpness from Miles Davis’ muted trumpet.
Beyond the tune, though, it’s a much more lopsided match up. The 490 undoubtedly has a much better sound stage, both in terms of width and depth, and has more stark instrument and layer separation. They’re also much, much more comfortable. I mentioned above that while I’d never really considered the 6X0s to be that clampy, a few weeks listening regularly to the 490 (and particularly rapidly A/B’ing them) has really brought me around on their clamp force being a little excessive. It’s easy to forget that I’m wearing the 490s; with the 660S2, I’m almost always aware they’re on my head, especially if I’m wearing my reading glasses.
I came into this comparison thinking that I was going to end up saying that while the 490 are great for many things (gaming, background listening, bassier music) I still prefer the tune of the 660S2 (and by extension the 6XX) and now that I’m here … I think that’s not true? I hate to say this, and I’m a little concerned about what I might say when I get to the 490 review and have to do the comparison to my beloved 6XX, but … I think I prefer the 490. And it’s … not that close. There are certainly kinds of music where I’ll prefer a slightly less bassy tune, but for those I can just throw the cloth (“mixing”) pads on the 490 Pro. My initial read was also that the 660S2 had the edge with resolution, but I’m much less certain of that after a lot of A/B’ing. It may be that there’s a little more there there with the 660S2, but the soundstage is so compressed and more crowded compared to the 490 that the net effect may be less perceived detail.
With the subjective stuff out of the way, let’s look at the graphs:
This is definitely in line with what I’m hearing; the 490 has distinctly better bass response and a little more treble energy on the lower end of the treble region. I’m a little surprised by the increased energy in the mids the 660S2 has; because of the way that particularly vocals carry through on the 490 I expected it to go the other way. It makes me wonder if my perception of more forward vocals is the result of a wider soundstage and better layer separation; it’s not that there’s more energy behind the vocals, but rather than they’re less compressed together with the rest of the mix.
Interestingly, when you put the cloth (“mixing”) pads on you get a much more equivalent bass response. I look forward to doing a deeper dive on this contrast for my 490 review.
The other thing to note in this matchup is that the 490 Pro is also substantially cheaper than the 660S2 at this point, by more than $100. Given that I prefer listening to them for tuning, comfort, and flexibility reasons, the fact that they’re cheaper just further solidifies it: I’m taking the 490 Pro for pretty much every situation.
[It’s also probably worth mentioning that the 490 Pro is a single-entry headphone, with an option to plug in either on the right or left ear cup. I’m generally not a fan of single-entries, especially Sennheiser’s single-entry lines, but this is a balanced single-entry and it’s … VERY well implemented.]
Focal Elex
I joke about the Elex as being a Super-6XX or “What if the 6XX but bass?”, and it’s only partially a joke. To me, the Elex does most of the things that the 6XX does but better, with the slight exception of vocals (where the 6X0 remain the vocal king).15
The bass is better on the Elex than the 660S2, but this shouldn’t be a surprise; the bass is better than on any of the 6X0s. I do slightly prefer the mids, especially vocals, on the 660S2. The one major knock on the Elex (like a number of Focals) is that the vocal presentation can be just a little metallic sounding, and this is true on a track like “Clair De Lune” where Christine Hoberg sounds a little like she’s singing through a metal tube. The treble on the Elex is also spicier than the 600S2; on “Hayling” around 2:45 some of the sparklies are borderline harsh but are substantially rolled off on the 660S2. The result of this combination is that there are some tracks where the Elex will not be particularly pleasant to listen to without EQ, especially at higher volumes, but on other tracks the 660S2 will feel thin or sparse compared to the rich warmth of the Elex.
I also, personally, find the older-style Focals very comfortable but there are people who develop hotspots on top of their heads. The soundstage is also slightly wider on the Elex, and I at least perceive more detail and resolution in their performance over the 660S2. I’m taking the Elex over the 660S2 every time, except maybe if I were listening to acapella music.
The graphs more or less mirror this experience; the Elex is decidedly more v-shaped than the 660S2, and I personally think that the Elex benefit from a judicious bit of EQ to sand off a little of the spice (and running from a tube amp, sometimes).
Meze 105 AER
To no one’s great surprise, I prefer the Meze 105 AER over the 660S2. It’s a challenging matchup for the 660S2 just because the 105 AER is so closely tuned to my personal preference for a warm, vocally-focused tune. Add to that the degree to which most Mezes are (to me) best-in-class comfort-wise (disappearing rapidly on my head), and it doesn’t feel like a particularly fair comparison.
The bass on the 105 AER is better in terms of quantity and pretty on par in terms of quality, but the microdynamics and punch on the AER are substantially better. I do prefer the mids on the 660S2, but it’s not by a lot and the 105 AER doesn’t suffer the same kinds of timbral distortions that the Elex does. There are certainly some tracks like “Claire De Lune” where the 105 AER can come across as being a little bright (particularly at higher volumes and out of certain amplifiers like the Chord Mojo 2), but that brightness also lends itself to the better detail retrieval and soundstage you get from the 105 compared to the 660S2. They’re also like $150 cheaper at current retail, which only further supports my preference for the 105 AER. Just for fun, the graphs:
Yup, that’s what I’m hearing. The mids are definitely the strength of the 660S2 compared to the 105 AER, but for me the mids on the AER are good enough that the gains in terms of detail, soundstage, and bass make it the clear choice for me of these two.
Hifiman HE6se v2
I struggled a little about whether this feels like a fair comparison; at original MSRP, the HE6se v2 (“v2”) was more than three times as expensive as the 660S2, and at current prices, the v2 is about a third less expensive. I’m not going to spend a lot of time here other than to say that they’re very different headphones with very different niches in my collection. I prefer the 660S2 for casual listening, and the v2 for critical listening. I did a pretty detailed comparison between the v2 and the rest of the 6X0s, and the same things apply to the 660S2.
Overall
Overall, the Sennheiser 660S2 is a really good product, worthy of its place in the 6X0 line. It’s probably not my choice out of that family currently, but unlike the 660S, that’s more a reflection of just how good things like the 6XX are both overall and in terms of value. If Sennheiser brings the pricing down to the $200 range, it becomes a real competition for the 6XX and especially the 58X, and there are certainly situations and genres where I’d reach for this over the HD 600.
The most interesting development for the 660S2 is definitely the HD 490 Pro, with its more aggressive pricing, flexible options with the swappable pads, and substantially increased comfort. In the same way that the 6XX substantially undercut the market for some of Sennheiser’s other products in the US (*cough* HD 650 *cough*), I think the 490 Pro runs the risk of doing the same, and it’s not geographically limited to the United States the way the 6XX is. It sounds like the 490 Pro’s pricing is getting even more aggressive in markets like India, and I’m really curious to see if Sennheiser at some point decides to cut production of the 660S2 in its favor, or if the 660 sees an S3 revision.
I like the 660S2. I’m going to hold on to it, at least for the short term, and give it some more time. It’s a distinct step up from the 660S, and I understand the market it’s targeting, but I’m struggling a bit to see where it should fit in a lineup with the 6XX.
Phil’s Matrix of Use
#reviews #headphones #sennheiser #6XX #anc #spatialaudio #meh #2025 #99noir #meze #sunglasses #overear #cans #hifiman #arya #stealth #editionxs #budget #hahahaha
- I signed up for an Amazon sponsorship a while ago and it’s unclear if I was accepted; this may or may not be an affiliate link. Don’t know how to check. ↩︎
- Not an affiliate link; I just really love this headphone. ↩︎
- I score bass, mids, and treble on a two part scale: 1-5 for quantity (5 being the highest), and A-E for quality (A being best in class, E being laughably bad). ↩︎
- For soundstage it’s also a two part scale, with the number representing the width and the letter the separation within it. ↩︎
- For comfort/fit, my scale is A-E with A being disappear entirely into the background and E being I want to tear my ears off to stop feeling these headphones on my head. I’ve never had an E. ↩︎
- But also my Mimir/Jotunheim 2 stack, and the Apos Gremlin amp just for fun. ↩︎
- Though I’ll do a little single-ended versus balanced testing, just out of curiosity based on my experience with the 6XX. ↩︎
- One thing that I haven’t answered to my own satisfation is why, subjectively, the 6XX sound quieter to me at a given volume from a given amplifier. Both are nominally 300 Ohm headphones, and both have a reported Sound Pressure Level (SPL) of 105 dB/1Vrms, so they should, in theory, be the same volume out of the same power level on the same amplifier but consistently the 6XX is quieter regardless of cables. ↩︎
- For whatever reason, the 6XX is slightly quieter at a given volume coming out of identical ports on my Chord Mojo 2. ↩︎
- Spoiler alert: I’m probably never doing anything where I’m going to care more about the appearance. ↩︎
- Sadly, I have returned the 58X Jubilee I reviewed to their owner, so I cannot do a direct comparison. ↩︎
- With the caveat that there are kinds of music I prefer the 600 for. ↩︎
- The Pro Plus comes with a third set of pads and a case, and maybe an extra cable? I can’t see paying that much more for it, honestly. ↩︎
- Depressing only in that I think the 660S2 compares pretty favorably to the 6XX, and one of my takeaways so far from the 490 is that they might, finally, dethrone the 6XX in my heart. And I have mixed feelings about that. ↩︎
- Every time I do one of these, I’m struck by how very much I like the Elex and am reminded my review of it is LONG overdue. ↩︎
Phil's Superpower of Enthusiasm 
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