HD 660S2 - Audiophile Open-Back Over-Ear Headphones with Deep Bass Extension and Refined Acoustic Performance, Headphones for PC, Music, Gaming, Podcasts, Premium Black

There are plenty of opinions on this headphone all over the internet. None are bad, but some are pretty negative. Mainly because from what I am seeing, the reviewers are reviewing the price, not the product. They are saying, you get almost as good performance from model/Brand A or B for less money, focus on the ALMOST. While yes it is true, at $600 is expensive, but make no mistake about it is does out perform other headsets in many areas. This headphone is on sale for $100 more than the HD650, which is $100 more than the HD600, so this falls right in line with Sennheiser pricing structure now, and rightfully so. I don't think it is double or triple the other two 600 series headphones, but it is IMHO is a much better headphone, and worth $100 more. Literally, if you are looking at the 600 or 650's and aren't sure which sound signature is for you, get this one if you have the budget, or wait a little while and save for it... It is worth it. It has the best characteristics of both, which you can see some reviewers stating this. I believe it was Josh Valour who said it, but I do disagree with something he said, it was something along the lines that is in between both models, and a jack of all traits, but master of none. Well, it is a more well rounded performing headphone than both of those and I believe it Masters an overall warm, smooth, well defined, spacious sound with impeccable imaging. For me and my taste it is the PERFECTING SOUNDING HEADPHONE, and exactly what I was looking for. No headphone is the everything to everyone. So be honest with yourself on what you like, based on your ears, and not popular opinions, even if it is from experts, which they are, I am not disputing that at all. I am pretty new to the whole audiophile thing. One thing. But, I have learned that you really need to spend some time with the equipment to let it sink in and let your hearing mature to the product at hand. I realized this, when I purchased the Harmnicdyne athena, reviewers raved about them. It sounded like the overall characteristic I like so I decided to give it a try. I received them, put them on and listened, I was horrified. What I hadn't realized was that my hearing was skewed by listening to the hd560s so much (I really enjoy that headphone). Doing A/b comparisons only made it worse for me. So, I decided to force myself to listen to them. So, I did, I listened exclusively for 2 days, and when I would take breaks and come back and listen to the Athena I was truly amazed at how much I LOVED THEM!!! It is really hard to compare headphones; they all have their own characteristics, just as we all have our own opinions and tastes. So, I believe headphone reviewers have a very difficult job. As some of us expect them to tell us what is "BETTER" headphone A or Headphone B, it just isn't that simple. Headphone A might be better for you, but headphone B is better for me. That is the beauty of this hobby. There is no right, or wrong, better or worse. Just learn to appreciate what your ears tell you and take all other opinions with a huge "GRAIN" of salt. Josh Valour, DMS, The Headphone Show, The Source Audio Video Group, and some others, does a great job of describing the products and giving a sense of how the product is. I watch way too many reviews. LOL. I Hope this helps someone else on the audiophile journey. Here is my current stuff incase anyone care to see. I literally started with headphones and amps a little less than a month ago. The gaming headsets, I have had for about 6months to a year, that is what started it all. I have the HD560s, HD 660s2, Hifiman he400se, Harmonicdyne athena, I am using the IFI Zen air line of products, the Air dac and Air can, both awesome to start with, and you probably won't need to upgrade for some time, key word is need, want is different. lol. For gaming I use the PC38x Sennheiser/epos, the epos H6Pro, Steel series Nova Pro wired with DAC. Sennheiser Game zero, and Audeze PenroseX, Gaming Dacs are the sound Blaster GC7, and G6 love them both but prefer the GC7 in case anyone is looking at the two. Good luck, and good listening!

Update on August 9, 2024: The iFi DAC combined with the iFi Zen Can produced clear sound and proper dynamics, but human voice sounded feeble and harmonics were missing (that is, a concert piano sounded like an electronic one). I figured it was the amplifier, not the headphones, so I gave a try to an XDUOO TA-10R, which is a hybrid headphone amp, using a balanced tube and Class A amplification (USB, optical, RCA, and coax inputs, a pseudo-balanced output that still sounds better than the 6.3mm unbalanced one). Once I swapped out the factory tube for a Gold Lion, the sound stage opened up, human voice became full, and the harshness around the high C vanished. Even poor recordings (uncompressed) sound good, providing a lot more presence than I experienced from the iFi combo. The fullest sound that goes deepest uses a Tungsram tube. I must admit that a $40 Koss would probably meet most people's need. Also, as my old friend said about 50 years ago, no headphone can compete with a good room setup (which can be hilariously expensive, but not necessarily. Compiling it from used items, you can get one for around $10k, which is still a lot less than the top-of-the-line headphones that still can't compete with it. Original review from May 24, 2024: Every time I put them on, I feel mesmerized. Have never had this experience with any other headphones; it's like the music comes to life around my head, as if I was present at the performance. Granted, that applies mostly to classical music, and the sound can easily bring tears into my eyes. Still, these babies produce excellent sound for everything I've put on them. I'm not a gamer, so I can't comment on the gaming performance, but there is at least one 5-star review on that subject. Anyway, beyond the subjective, sources and recordings are also essential to consider as well as the connections, so let me submerge into those details. Good headphones are no good for compressed sound, but plenty of headphones are made for such a clientele. The s2 with its refined sound is targeting an audience that cares for the original sound. Please, notice that when people "burn in" new equipment, during much of that (except for diaphragms in speakers), what happens is that the components adjust to each other, especially on the analogue side. The outcome ultimately determines if their combination is feasible or not. My current setup has been serving me well in the last five years or so, so I haven't made any changes. I used an iFi Zen DAC v1 (from the USB port on computer) and an iFi Zen Can v1 (on the RCA input from a relatively high-end LG Blu Ray player from the optical port through a digital-to-analogue converter). Connected the DAC with the amp through their balanced ports with a short decent balanced cable. Both amps were hooked up to the sources with SVS interconnect cables. Didn't use the "Trubass" feature on either one, because for my taste, it upsets the sound balance (the DAC also amps the bass at a higher frequency than the amp). My sources were the usual high-resolution recordings (both pop and classical) and Blu Ray movies I use for testing new components. The most prominent strengths of the s2 is extended bass and an adherence to the original sound signature. While the OEM cables are fine, out of the two supplied, I favor balanced one. I have found a purchase for a previous Sennheiser that didn't work out at the time giving me better resolution. Amazon is still selling it: KK Cable II-SO. (Added on 6/28/24: for movies, the original balanced cable works better; the KK produces less bass in return for better instrument positioning, and dialogues suffer from human voice being elevated around 500Hz, which makes conversations harsh and unpleasant to listen to. The original cable goes deeper, although perhaps a bit muddied in the lowest end, but conversations are clear). The only problem with the extended bass is that the housing loses a little control over it beyond a certain (obviously VERY high) volume, so I can sort of feel the ear cups moving, which breaks the illusion of being present. This is probably the main reason why the pressure around the ears is relatively high (and loosening it might not be the best idea). The s2 might not be the best for someone with a large head (it might feel uncomfortably tight) or unusually large ears that the ear cups cannot cover, and it took me a few days to get used to it, because I am on the high end of average head and ear sizes. The included bag is a plastic dust collector; I am using an anti-static bag instead. Hard cases are available for transportation, but the original box works for that, if only on occasion. As opposed to the planars I've heard (Moondrop Para and Hifiman HE400se, but others report the same problems with lot costlier planars), the s2 retains the familiar sound on the recordings I usually use for testing new equipment, and it extends the listening experience in gentle, but important ways. The bass reverberates in the concert hall, and is not victim to extensive channel separation. Even harmonics play the same or better than on anything else I've heard in this price range or below, although this is a feature that can warrant higher investments. No problem with high-pitched human voice being harsh and sibilants don't suppress other frequencies; the performance is actually toned down a bit in order to retain the sound that recordings must have been meant to sound like. In my understanding "warm sound" is often used for describing the feature, perhaps because no highs and mids dominate at the expense of the bass or each other. Despite the somewhat reserved (but not veiled) presentation, the dynamics don't suffer. I believe, the secret is ingenious engineering that uses physics: the proper driver and built-in sound paths in the earphones. Many other headphones have built-in electronics in the sound path, allegedly, to protect the user's hearing, but to me, it seems more like protecting the drivers from overload. Consequently, the s2 doesn't clip at low bass (emit a clicking sound, while cutting out the sound), while most the sound is there in that region, too. The headroom is like sitting in the concert hall, albeit a bit further in the back that the eight row, but the sound image remains steady at various volume levels. To me, the harmony and the unity of the sound, along with the original sound signature, is worth the price. Added on 04/03/25: The best cable I've found for these is https://www.amazon.com/gp/product/B0BZMS68RV, although it lasted only for six months. The best amplifier in this price range is a hybrid tube (the tube is only for buffering a Class A headphone amp) is the XDUOO TA-10R. Added on 12/22/25 The best affordable tube headphone amp for these turned out to be a Fosi GR70, available on Amazon, where I also bought it for under $180.

Retired multimedia professor—audio production was my research field. 27 years experience. I’ve owned dozens of headphones. These are right up there with my favorites, some of which are pictured. Purchased in March 2024. Impedance is 300 ohms, so they require clean power. I typically use them with a Chord Mojo 2 DAC/amp or with my Universal Audio powered studio hp out. Smooth, sweet, accurate, not scooped and not bloated below 150Hz. No QC issues on my end. Replaced the cable and ear pads after 1 year of heavy use. Spare parts are easy to find. Good detail but they are not Beyer’s or Focal’s; just a silky smooth ride with decent power and source material. They love a great turntable and tube hp amp like a Schiit Valhalla playing well cared for vintage vinyl. Probably not robust enough build to be stuffed in a backpack or kicked around a hotel room. My go to for recreational listening. Use them in my studio as well.

After much internal debating, I decided to pick these up. The sound quality is very good, though the headphones lack a little oomph in the mid range, given the price point. They do actually have a good bit of bass as advertised. The real place where these headphones shine is the imaging capabilities. In CS:GO I can easily pinpoint where enemies are at based on their footsteps. For competitive FPS and tracks where imaging is very important, these headphones bully a lot of other headphones. The drum fills on Animals As Leaders - Parrhesia and a lot of Fela Kuti tracks are insane on these headphones. That leads me to the price point. These are amazingly good headphones in the imaging category. As for pure music use, I personally tend to go for a more of a relaxed listen for a lot of my library. Don't get me wrong, there's a lot of stuff that I have that I can see why these are so great, but for the average listener I would not recommend these purely as music headphones. If you're strictly listening to music with these, I think a pair of 650s would suit you well, especially if you're not listening to more energetic music. These still play well with all of my library, but the price point is at lot, at the time of me writing this. Now, if you're wanting a more forward listen, these are great. Everything sounds so much tighter, response wise with these headphones. You can really hear the intention of the artists with some tracks with these, especially in higher bitrate recordings. These headphones are great for competitive gamers where spatiality is a must, and great for stuff like Jazz Fusion, Metal, Rock, IDM, Electro and some Rap / R&B. I've not listened to much vocals with these yet, I'm not too big on vocals in music, so that's still to be seen.

The headphones are amazing. Super balanced. No complaints at all. Perfect low end and high end. It makes me really love listening to music. They sound even better with a nice dac/amp combo, but even with a portable dac/amp like a ifi go link max, I get great audio out of them using my macbook. I smile every time I listen to music with these. Amazing. And they are great for the price!

Got these cans for 400 dollars for black Friday. SOUND: These headphones sound better to me than the rest of the 600 series simply due to their better sub-bass performance. They have a pretty wide soundstage, have excellent instrument separation and sound good with all music I have thrown at them. The mids perform excellently, just as the rest of the HD600 series, and the treble is sparkly and nimble but not fatiguing. These are a good, balanced, warm sounding pair of headphones that are well worth the price that I bought them for, however I could not recommend these for $600 as this price forces competition with a higher class of headphones. COMFORT: These headphones are the most comfortable pair I own, with nice soft earpads and a perfect amount of pressure that gets a good acoustic seal over my ears. My head is on the larger side, so as to the issue of clamping force, I really did not feel that they clamped too tightly. These are the kind of headphones that I could wear comfortably all day and forget I even have them on. DRIVING EQUIPMENT: To those that have mentioned an unimpressive performance from these headphones, when used without a headphone amplifier or properly specified piece of equipment, these headphones tend to sound a bit soulless, empty, or a bit muddy. However, the great thing about the HD600 series is that they tend to scale very well with good sound equipment. The difference in sound that an entry level Schiit DAC+Amp stack made was well worth it and really made these phones come to life. This does mean, however, that you should also consider the cost of an amplifier and DAC unit as a cost included with these headphones, so at minimum another $200 added onto the already expensive price. There are many other good options for headphones that are easier to drive and do not require a dedicated amp for this price range, so if this isn't for you, I would look elsewhere. Overall a great sound albeit a bit overpriced at MSRP.

If you are reading this, chances are you’re stuck in the exact same predicament that many of us find ourselves in at some point, including myself recently. Which HD6** series headphone would suit me best? Despite reading hundreds of forum posts, analyzing dozens of squiggling graphs, and scouring in-depth reviews for that potential “ah-ha!” moment that would convince me one way or another, I still found myself going in endless circles deciding on what to get. I started with the HD6XX due to its ridiculously good price when on sale ($179). With how impressed I was with it on my xDuoo TA-66, I just knew I had to try the others. Naturally, nothing in audio ever seems good enough, and once again I succumbed to the curiosity that something “better” was right around the corner. And now we’re here. The only real difference between the three as far as “what's included” are the cables. HD6XX has a 4.5ft terminated into 1/8th (with adapter), HD600 has a 9ft into a 1/8th (with adapter), and the HD660s2 has two 6ft into a 1/4th and 4.4. HD600’s cable is the thinnest and most flexible, but both the cable and connectors are quite a bit smaller and don’t seem as durable. Other than the extra cable the HD660s2 includes, it also comes wrapped in a microfiber bag instead of a plastic bag like the others (must be where all that extra cost comes in). Jokes aside, physically all headphones are nearly the same with slight variations in frames, color, and swivel. HD660s2 and HD600 have flatter earcup frames whereas the HD6XX is more rounded. The HD6XX also has slightly less swivel range but is less creaky, whereas the HD600 and HD660s2 had a bit more swivel but there was more of an audible rattle when handling or setting down the headphones. Very minor and in no way a flaw, just something I noticed. A word on amplification and gear. I'm using the Topping DX5 as the DAC (sometimes with the headphone out) and the xDuoo TA-66 OTL tube amp. In conjunction with the stock tubes, I’m also testing RCA 6AS7G and 6080 for the rear, and Gold Lion 12AX7 (with adapter) and Voskhod 6N2P-EV for the front. Some combinations I’ve definitely liked more than others, but the stock tubes are FINE! Having owned the HD600 and HD650 many times in the past and heard them on a variety of equipment, after hearing them on the TA-66 I can confidently say these Sennheiser’s really DO need tubes to sound their best. And for $250, I simply cannot recommend the TA-66 enough. I do believe an OTL tube amp is essential for any of these headphones as the sound changes/gains are quite obvious. Match made in heaven. So the adventure began with the HD6XX and the TA-66. I was so overjoyed with this combo and quite honestly, I’ve never heard the HD6XX/HD650 sound this good! My favorite combo was the RCA 6080 and the Gold Lion 12AX7, both waking up the HD6XX and injecting it with more energy. However I was NOT a fan of the RCA 6AS7G as it made them sound really mushy and strained. With how much I was enjoying the HD6XX this time around, I knew I had to get the HD600 once more, having preferred it to the HD650 in the past. To my surprise, I didn’t necessarily… like it more? While the slightly more neutral sound signature was nice for some things, the HD6XX had a more pleasing and likeable tone. The HD600 could sometimes sound a tad thin in comparison. Honestly, both were so close and kept trading blows to the point where I couldn’t choose between them. Thus, the tie breaker is price. HD6XX takes it. Next up, the HD660s2. Having never heard these (or the originals), I wasn’t sure what to expect. I went into it fully hoping that they would be a clear winner with their “extended bass” and other tweaks. I had to do a bit of mental gymnastics to get past the price in comparison to the others ($399 on sale), but I told myself that if they were the tiebreaker and I generally preferred them to the other two that I’d keep them despite representing the worst value of the three. Immediately upon first listen, I did NOT like them! What was this? Bloated bass, darker sound than the HD6XX, a slightly wonky tone, and no noticeable technical improvement in any other area? I was beside myself. This is Sennheiser’s latest and greatest HD6** headphone? First thing that came to mind was the HD700 with Dekoni pads. Was not a fan of those either for the same reason, but at least those were more comfortable and had a larger soundstage. Bass is what you notice first and foremost, and it distracts you from the magic mids. All things considered, the bass isn’t great either. Don’t be fooled into thinking this is a HD600 or HD6XX with “deep bass”. If you want headphones with deep bass, you’d be better off choosing planars or closed-backs. Another way of putting this is to think of the neutral reference HD600 as a “0” on a scale representing its level of bass, treble and sound signature with each sequential number decreasing treble, increasing bass, and sounding warmer. The HD6XX would slot in as a “1”, a little less treble, a little more bass, a little warmer. HD660s2 would then be a “3” as I think the difference from the HD6XX to HD660s2 is larger than the HD600 to HD6XX. The DT880 would probably be a “-1” on this scale, being colder and brighter sounding. Honestly, after following up listening to the HD660s2 with the HD6XX, the HD6XX sounds like it should be the HD660s3, because it “fixes” the flaws I had with the HD660s2. I just don’t get it. HD6XX and HD600 are clearly sidegrades to each other, whereas the HD660s2 is a downgrade in my opinion. Focusing on just the HD600 and HD6XX, these are some of my favorite headphones of all time. Their glorious midrange is still unmatched and I have yet to find a headphone with better tone or timbre. The only other headphone I can recall liking more overall is the HE1000 Stealth. Despite my preference for light bass (I use Magnepan LRS+ with no subs for example and LOVE them), I actually lean more toward the HD6XX than the HD600 which surprised me. I think the HD6XX synergies with tubes a bit more and the sound seems just a little smoother, more cohesive, and more weighty. I think the HD600 is objectively the better headphone, with the HD6XX being subjectively the better one. My brain says HD600, but my heart says HD6XX. Again, very minor differences between them and both are incredible headphones, but the HD6XX is unequivocally the no-brainer simply because of its price. On solid state amps, I find this series can be too mellow, uninvolving, or restrained, but tubes really capitalize on their strengths and are the key to unlocking their full potential. Let’s recap real quick and see the current standing. So we have the HD6XX around $200, the HD600 around $300, and the HD660s2 around $400. The HD6XX and HD600 are too close to call making the extra $100+ not seem like a good investment, yet here we have the HD660s2 which is unquestionably in 3rd place… yet they are DOUBLE the price of the HD6XX? Absolutely not. At the current pricing structure, quite frankly, the HD660s2 is a joke. Do I think the HD600 and HD6XX are $300 headphones? Absolutely. How about the HD660s2? No way. I think they sound like a $200 headphone at best, but based on the HD6XX’s price, I personally would not pay more than $150 for them. By the same token, I also do not think the HD600 is worth $300+ considering the market disruptor HD6XX can be had for $179 or $199. That being said, I don’t think the HD660s2 is a bad headphone. In fact, I still did enjoy it once I got used to it. No doubt its flavor would appeal to some over the HD6XX or HD600 in direct comparison, but I emphasize “direct comparison”. Because at the end of the day, I can’t stress enough just how similar all three of these headphones sound and to just buy whatever is cheapest or most available to you. Case in point, of the many hours I was comparing these three, I can’t tell you how many times I would lose track and literally forget which of them was on my head, only to be blindsided when I pulled them off thinking it was one of the others. This really proved to me that once I started listening, the finer details and small tuning differences faded into obscurity and I was then just listening to a “Sennheiser” headphone. Wrapping up, the biggest discrepancy with this trio of headphones is undoubtedly price and value. So what do I recommend? If you don’t own any of these headphones, get the HD6XX when it's $179, a TA-66 for $249, have some fun rolling tubes, and enjoy the music! The tube swaps provided a bigger sound quality change than switching between any of these headphones and for a whole lot cheaper! And if you already own one of these headphones and are tempted to purchase one of the others hoping for an upgrade or just a different flavor, don’t bother… you only need one HD6** headphone. Famous last words: “you only need one”.

Quite a few people will say these headphones aren't great for gaming. Ignore those clowns. Video Games: 10/10 The issue is that 95% of headphone reviewers when asked "what makes a good pair of headphones for gaming" - almost exclusively look for the widest soundstage possible and super clear treble. Which I mean, is great for pinpointing footsteps. But there are people out there who play more than just FPS games. If you're a solely hyper-competitive FPS gamer, maybe something from the Hifiman/Beyerdynamic lineup is better for you. But I would recommend these cans for everything else. If you play any games that are immersive in nature or are known to have good sound quality, such as Cyberpunk 2077, Elite Dangerous, or Elden Ring. You will love these headphones. But, even in games like Rainbow Six Siege, I didn't perceive any noticeable drop in my perception of where people were compared to my old cans which were the HD598 CS. In fact, that aspect is pretty much the same, and hearing gunshots and explosions in Rainbow Six was pretty jaw dropping as well. You can hear the rumble of an impact grenade from the other side of the map sort of bellow in your ears. The low/deep growl of a deagle firing off sounded impressive as well. I did EQ mine on the low-end to output some nice rumble. Cyberpunk 2077 was easily the game that blew me away the most. It legitimately sounded like a different game to me - it's THAT drastic of a difference. I heard things I hadn't heard before - as if this is how the game was MEANT to sound. It literally makes me feel like I'm there when I hear cars rumble past me on the street, and I think it's as close to life like as you can get from a pair of headphones. In another instance, there was a highway above me and surrounding me was a market full of people talking, in game music (like from radios), advertisements, etc - and I feel like I'm standing there, in the market. Imagine the cars from above encompassing your entire soundstage in the background, like further away, but the details of the market still sound closer and don't lose their detail. Music: 9/10 For music, there's plenty of other reviews that cover that, but these don't disappoint. I mainly listen to video game OSTs, rock bands like Cage the Elephant, or metal like Sabaton. Definitely an improvement over my old 598 CS. Movies: 8/10 I haven't tested these out with movies/TV shows too much so I can't give a fair opinion on that, but so far they sound good, nothing yet that has super impressed me. Comfort: 9/10 These feel fantastic, some people claim the clamp force is too tight, but it feels just right on my normal sized head with normal sized ears. They might feel a bit tiring to wear for prolonged periods, but supposedly this will subside with time. Overall: 9/10 I am truly impressed by these headphones. The details, bass, sound quality, and imaging capabilities of these blew me away. Easily worth $400 on sale. If anything, it makes me appreciate the source of audio I am hearing more. For example, I can more easily tell if a game had a higher quality audio team working on it, or if a song was produced in a studio vs some trash recording. Sidenote: I am someone who likes emphasized bass, neutral mids, and neutral treble. I find emphasized treble to be annoying and shrill to listen to. I was also that kid in high school who would have to cover their ears completely during fire drills (and it seemed like I was the only one) - so if that sounds like you then you probably have the same tonality preferences as me. I also tested these with a Fiio K7 and Fiio E10K as my amp/dac sources.