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

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.

Sennheiser HD 660S2 - Audiophile Open-Back Over Ear Headphones with Deep Bass Extension and Refined Acoustic Performance, Over-Ear Headphones for PC, Music, Gaming, Podcasts, Premium Black I’ve actually bought these headphones three separate times now. There seems to be an ongoing price war between Amazon and Best Buy to see who can drop the price the lowest, and I kept chasing the deal. If you can snag these for under $420, they are absolutely worth it. If the price jumps back up toward $600, keep an eye out for the refurbished models that pop up around $350—they are what the product should be priced at. I’m currently running these through a Fosi Audio DS2 (the 2024 version) for both my PC and my portable gear. I use the 4.4mm balanced connection, which provides plenty of power to really let these breathe. If you’re using a standard headphone jack, your results might be a little different, but with a decent little DAC like the Fosi, they shine. The standout feature for me is how intimate and lifelike the vocals sound. Because the DS2 has a very neutral, "clean" profile, it balances out the natural warmth of the 660S2 perfectly. It creates a really relaxing, rich listening experience that doesn’t get tiring after a few hours. I bought these specifically for critical music listening, and they nailed exactly what I was looking for. In terms of the actual sound, the "stage" feels a bit narrow and close to your ears—it’s not a wide, airy stadium sound—but the bass is warm and has a nice punch to it. It feels impactful without being overwhelming. I also own the HD 490 Pro and the Fiio FT1, and they all serve different moods. While the 490 Pro is wider and better for picking out every tiny detail in a mix plus I also use them for gaming using custom audio cables from Hart Audio, and the FT1 is a "disruptor" with deeper bass because it’s a closed-back design and under $170, the 660S2 is the one I reach for when I just want to get lost in the music. It’s a premium piece of gear that feels like a long-term investment for anyone who loves high-quality audio.

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.

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!

This is my first pair of open-back headphones. I purchased them to study in a basic audio mixing course I'm taking. I'm not an audiophile by any means and for my 50+ year old ears, these sound quite good. I needed a pair of reference headphones that don't color the sound, so that as I learn mixing, I can make sensible decisions once I get to the part in the course where mixing in headphones is covered. Overall, I think the sound is great given the concerns that many people have expressed in Sennheiser's frequency response chart on the product page of their website in that there's a trough around 5K. That could certainly be a deterrent, but I think the overall balance is good without the sound being too exhausting over long periods of time. The pads feel great and are very comfortable even with my glasses on with not too much pressure. I have a lot of hair on the top of my head, so I don't really notice any pressure on the crown of my head either. My only gripe is regarding the choice of cables. First, they offered a balanced 4.4mm plug, but an unbalanced 6.35mm plug and a dongle for a 3.5mm plug for mobile devices. At this price point, it would've been nice to include a balanced XLR option. Second, the cables are too short for my liking. I recently purchased a DAC and headphone amp along side this purchase and positioned it on my desk next to my monitor controller. Because I have an 88 key MIDI controller directly in front of me for my music production, I couldn't flop the cable on top of the keyboard, and the cable was too short to run around the edge of the keyboard. So I ran the cable under the platform the keyboard sits on and it was just long enough to reach. But if I sat back in my chair, it would tug on the cable. Fortunately, I also purchased a replacement cable with an XLR plug and it's longer and that leads to...... Third, the cables that come with the headphones are non-microphonic until you get to the part where the wires separate to each cup. The part of the cable that extends to each cup is susceptible to annoying noise when it touches anything from clothing to fingers. A slight move of your head transfers any contact with the cables straight to your ears. Not acceptable in my opinion for this price. But overall, I am pleased with the purchase and plan to use them for years to come.

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.

Not worth grabbing at retail price of $600 but when on sale at around $430, absolutely worth. The sound is not as neutral as the HD600 but for casual listening, I would say it responds better than it's predecessor. Sorry for the wall of text incoming below. The transducer is warm and open with exceptionally neutral mids, resulting in clear vocals and instrumentals. With higher output levels, the mid-highs can become a bit harsh so I suggest cutting them with an EQ. Also the distortion threshold is so ridiculously high that your eardrums would probably pop before it crosses the 1% threshold. It's amazing how clear these headphones sound at higher output volumes. But for how little distortion there is, the soundstage leaves a lot to be desired. Even with the open back design, the soundstage is limited by the 38mm transducer size where it's competition has all moved on to bigger transducer sizes. It is easy to live with at the sale price, but I would not recommend it at full retail. One thing that should be very clear though, this is not a headphone for traveling, or for office use, or for gaming, or for anything else other than sitting at your personal desk, listening to music. That's it. Kinda niche but it is what it is. It doesn't pretend to be anything it's not so it isn't for everyone. The target audience is so incredibly small that this headphone gets lots of poor-average reviews on various headphone rating sites because of how small it's target use-case is. Comfort-wise, it is enough to wear all-day but tends to fit smaller heads more comfortably. The padding is ample and can be easily removed for cleaning or replaced. As for Pre-amp/DAC suggestions, if you have budget leftover, I would go for something like a FiiO K7 or K5, or an iFi Zen V2, or TempoTec M3 (in order of decreasing price). There are other options but I went with a FiiO K7 and do not regret it. TLDR; Again. This headphone is pretty much a really expensive way to listen to music. That's about it.

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.