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!

Out of the box it sounds really good. I'm new to the Audiophile world but this has the best mids I've heard from headphones, great treble. It's lacking a little bit in bass and sub-bass but it's still not bad at all in that department. Using Oratory1990's EQ is what really made these headphones shine for me, it left 98% of the highs and mids but fixed a lot of the sub-bass dropoff. It's very comfortable, especially with the open-back design. Not too big or heavy for your head. You can wear it for hours at a time without it hurting, unlike my old Audiotechnica headphones.

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.

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.

Expect a highly engaging and generously spaced-out soundscape. In addition to the wide stereo field, there’s a real sense of depth here. Instruments can really sit behind the head on these headphones, whereas on so many dynamic headphones, rear-positioned instruments seem to be contained to the stereo boundaries. But here, you’ve got a truly multidimensional feel. Although you won’t hear soaring heights in instrument placement, the HD 660S2 does seem to elevate instruments, especially in the upper-mids, adding to the floating quality of the sound signature overall. And I would say, as far as reference headphones go, this is one of the most enjoyable soundstages I’ve experienced. I would even venture to say that the soundstage beats some of the more expensive planar magnetic models on the market.

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.

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!

Sennheiser. Wow, where to start. I tried several different models, and decided on these. These are the pricey ones - are they worth it? That depends on you and your equipment. To get the best results from these headphones, you MUST have a quality, high-powered headphone amp. This was not made clear enough in the pre-sales information. If you don't have a good amp, or one incredible sound card in your machine, you are not getting the full potential out of these - so there is an extra expense to consider on top of the already high price of these cans. Connecting these directly to a hi quality receiver works fine too. Now, the next issue - these are OPEN BACKED headphones. I knew that when I purchased them, but these were my first pair of open-backed cans. I chose this model because the reviews and descriptoin stated that these phones had the best low-end. The words "sub-bass" were even used in the product description multiple times. I am disappointed in the low-end performance. Additionally, due to the fact that these are "open-backed" headphones, anyone else in the room with me when I am listening to them can apparently hear what I am listening to quite well - so something else to think about. Now a word about quality. Sennheiser has a reputation for putting out some top-notch hardware. I cannot argue this point. The build quality was great, they came with two sets of cables - one balanced, one not. When I did get an external headphone amp with a quality DAC, combined with some quality content from the likes of Qobuz, Tidal, or Deezer, and these headphone prove their worth in spades. The high-end, the details, the vocals - oh my goodness do these things sound good. PROS: Solid Build Quality Multiple quality cables included With the right hardware driving them, they sound incredible CONS: Expensive Require additional headphone amp or ONE HECK of a sound card Sound is quite loud and clear outside the headphones Missing Low-End Punch Expensive I actually love them when I am able to listen to them when there is nobody else in the room because of how loud they are on the outside. Would I recommend? If you have the money to spend on them, and Low-End means less to you than incredible detail, sparkle, and vocals, then yes, I would recommend them. If you are really in to low-end punch, and/or don't have the $2k or so to invest in both the headphones and the proper amp to power them, I would recommend going a different way.