Sennheiser X Massdrop HD 6XX

I got these because I had the DT 880 and wanted soemthing that was darker while still being neutral and not too expensive. These were recommended to me as fitting that bill and also being similar to the HD650, so it would also give me a chance to hear what others people frequently reference. That is one of the main reason I bought them as well, they were something tons of others have tried and I could compare my opinion to theirs to get a good internal reference. I used them with the CEntrance DACport HD.

Build Quality, Looks, Packaging
They feel "cheap", as in lightweight and plasticy. But, I actually don't mind this at all, so don't think of it as an insult. I just wanted to mention that because I feel someone will equate that with not “feeling premium”.

I think the headphones look ok. They are navy blue and black, however I think it would be better if they were all black instead. That would give them an aesthetic somewhere between a professional and midnight vibe. The design of the openneess also looks great and it kind of reflects light back though. I love looking into the outside when I pick them up every once in a while.

Instead of coming with a normal carrying case or pouch, it comes with this this big box which I hate. It's not travel friendly ONE BIT, it has a cutout to place the headphones in which isn't even fully snug or designed well, and the box is prone to getting easily dirty and its hard to clean or the material comes off. I'm going to sell my pair and the box already looks a bit like hell, and I've barely done anything to it. Why? Just why?

Fit
This is a tight headphone, but more than that, I'm not a fan of the earpiece shape. It’s like it's not circular enough. I'm not sure what, but it is a finicky shape and fit on my head with regards to positioning it forward or back or low or high. With these, I like to wear them slightly up and just enough forward to make it sound "right", as I find wearing it low sits on directly on my jaw bones and though it sounds a tad bit wider and treble-y, it's not in a good way, it doesn't sound like it was intended or designed to sound like that. The main problem is I feel like the back of the left headphone touches my ear too much or just fits in a way I need to fuss with. Not a pick it up and go headphone.



Sound quality
Overall, I would say that these headphones sound tall/tight, speaker-like, and warm.

Bass
It has bass, but not how I expected. The sub isn't very much. When I think of dark or warm sounds, I would say dark is more deep and murky (black), and warm is less than black, it's a brown color, it's a tilt. This is like a medium brown, not too dark in shade. They have a little bit of a tilt to them but are not extremely bass heavy. Is it good enough for me? Considering I listen to a lot of EDM (not just the “genre” EDM, aka mainstream club hits, but electronic dance music in general), I would say it’s not enough for any kind of slam but it’s not bad. I was looking for something along the lines of neutral anyways. I would like more sub though.

Mids
These headphones are all mids. I feel like the entire section is highlighted. It's present from the very first use. Something about this sounds speaker-like too, like it's similar to speakers, not a "headphone sound". This is a pro and a con IMO. It's good because it's more familiar and what I am used to in my mind, but also bad because it feels a bit off from other headphones I have experience with. Compared to my previous headphone though, DT880 250ohms, it sounds a mix of way more lively, aggressive, and “correct”.

Treble
A bit rolled off, not really sure what else I have to say. It's just smooth, non-piercing, etc. I think I can hear part of the famous "Senhessier veil". Try songs like Hannah Diamond – Fade Away. That song has a quite bright female vocal and while it won’t take it away, it’s a bit less airy.

Imaging
Imaging is ok, not sure what else to say as it wasn’t something I tested or even stuck out to me when I was using them. Some of those "8D Nation" youtube videos sound ridiculously realistic and good on these.

Soundstage
The main reason I'm selling these headphones. It's like an upright rectangle. The sound has "height" and tallness, but no width. I want to be able to distinguish different tracks in a song with ease and that is not possible with the HD6XX. Even songs like "Solo" by Clean Bandit (featuring Demi Lovato), the bass line gets shoved into the vocals on the second chorus, like merged. Stuff just becomes less intelligible. I think they are below average in this area and it's a big deal for me. I even did a little bit of research after to see if I was the only one with this issue, but I'm not. Even with cheaper headphones, I don’t find it this bad. I find they have that "forced" sound I hate so much as a result, like I am just shoving a speaker in my ear or have the volume too loud and I can't easily focus on or hear things as a result. I need to have a certain amount of space and LACK of perceived volume to be able to use them. It really is like sitting with my nose touching my computer screen and complaining that I can't make out what is around me or being mentally suffocated.

OVERALL
I'm glad I tried these but they were a fail for sure. There was a small honeymoon period as I liked them for the things that the Beyerdynamic DT880 lacked, but as I got used to them, it went to crap. The soundstage is way too small and fit needs work. I would like something less mid-centric, sub-bass increase, and with a lot more separation. Before this I had the DT880 and these headphones really could not be anymore opposite. The Beyerdynamic has soundstage and comfort (!!), however it sounds synthetic and unnatural at times. The HD6XX has more realism and balance, however the fit and soundstage are nowhere near good enough IME.

I will try the Audio Technica R70X next or the AKG Pro 712.

I bought these used. Then washed the pads. I did listen to them a but before washing the pads, and after drying the pads it sounded the same to me. Used pads may mean that I had much less treble than new pads would.

Used just a q5k with a 3.5mm jack unbalanced to power these. Adequate volume was achieved, and when I tested it on my motherboard it was loud. I am told I may have found the 6xx tolerable with a bright source.

The 6xx is relaxed and inoffensive. At no point using these did I find my music sharp or sounding unsettlingly wrong. There is a pleasant amount of note weight on this set, especially the mid bass. I have no qualms about the mids, and actually, found the mid treble very adequate and correct timbrally.

To me, the bass sounded like wet cardboard, flabby, dense and wet. I enjoyed this sound personally though I wouldn't call it the most correct to me. There is not enough sub bass.

There was nothing to say about the mids; I had no qualms with the mids but also no praise. My nitpick is that female vocals sound pushed back at times.

The treble is clean and clear, and not particularly exciting.

The separation on mids and bass is average. I found it not enough, and it contributes to a poor sense of detail. I could hear all parts of my music though; think of it like a fuzzy picture. Sound bleeds together even though its all there. The treble escapes this poor separation however.

The presentation of sound feels vague. Somewhere around my head. Difficult to pinpoint things in playback.

I generally listen to more female vocal oriented music, and a lot of electronic music.

After listening to one slow ambient song, that usually felt ominous and intense as the plodding bass increased in energy feel pleasant and mild, that sealed the fate of the HD6xx as being labeled unengaging by me.


I feel cheaper IEMs are competitive with this headphone in terms of detailing and tuning; at the bare minimum, excel at sub bass.

I do praise it for being fairly correct, having decent resolution and being a relaxing listen for the price. It is not a bad headphone. The HD6xx is good for the price.

Rating: 8.6
Sound 8.7

Life is not a rainbow-colored unicorn, so you can't really blame the HD6XX for trying to stay authentic.

Click to expand...

Sound: 8.7

Handling: 8.5

Total: 8.6
Price: 185 €



Intro
DROP (formerly Massdrop) is in the end nothing more than an online shop. But with the subtle difference that they also put their resources into product development with well-known big players. In most cases, the aim is to revise or reissue an existing product, make it more cost efficient and thus make it accessible to a wider audience. Examples are the AKG 7XX, HIFIMAN HE4XX, or the SENNHEISER HD6XX, which is based on the HD650 in terms of sound and appearance. This is still listed at SENNHEISER for 459 €, but is available at Thomann for just under 340 €. Well, the HD6XX is available via DROP for about 185 € and that without big differences in processing and sound (if you can believe the manufacturer, since I can't make a direct comparison at the moment). DROP also produces on demand and therefore in different batches, hopefully with the same quality control. So the product is not available on the shelf, but only exclusively through DROP and therefore not permanently.
Soundwise you should be able to get something out of the SENNHEISER house signature, which is usually a bit more reserved and neutral, warmly tuned, at least when we talk about the H5XY and H6XY models.



Handling
Keyword cost efficiency. The HD6XX, consists of a good 80 % of plastic. Only the reinforcement on the headband, which also allows the headphones to be adjusted to the shape of the head, and the back grills of the ear cups are made of metal. However, the HD6XX does not make a cheap impression, because the workmanship is of high quality and no production errors or rough tolerances can be detected.
The earpads have a velour cover (which crunches a little bit with glasses), which encloses the complete ear and fits very securely due to the (a little too tight) contact pressure of the housing.
On the headband there is a foam padding, which prevents pressure pain as far as possible and allows wearing the headphones for a long time.
The wearing comfort is therefore good, but somewhat limited by the high contact pressure and the somewhat spartan padding on the headband. I prefer a flexible headband.

The accessories are reduced to a minimum, i.e. a 3.5mm cable (1.8m) and an adapter to a 6.3mm jack. The cable consists of two quite thick strands (left/right), which are led parallel. The connection to the headphones is done via a 2-pin connector (both sides). With the detachable cable you have the possibility to use the HD6XX balanced, whether with an adapter (25 €) to MMCX, or 2-Pin 0.78mm (a balanced cable to 4.4mm, or 2.5mm is required), or with a quite expensive balanced cable directly from Sennheiser.
We don't get much, but we get the most necessary, which is quite sufficient in terms of price. Here, the headphones themselves are clearly in the foreground, and even without accessories, the price would justify itself for me.

One cannot speak of isolation due to the open construction, which makes the HD6XX only suitable for public use to a limited extent, whether on the street or in the office.



Sound
Bass
The bass is quite linear, with a slight drop in the subrange. Therefore, it is more emphasized in the mid-bass without being exaggerated, but still close to the neutral ideal. I would like to see a bit more punch and firmness, but when it comes to fun in the low end, the HD6XX likes to give the sceptre away and prefers to limit itself to a natural response and realism. For me it would be close to the ideal if it would give off 2-3 dB in the upper bass and add this to the sub bass. If you prefer a well-dosed, natural bass, which is a bit softer but not muddy, the HD6XX is the right choice.

Mids
For my taste, the mids are the heart of the HD6XX. However, I understand also such opinions, which describe them as somewhat veiled and conservative. Well, they certainly don't have a WOW-factor, but they are damn natural in their presentation. The point of criticism is the clarity, so I go with the first argument. But only to a limited extent, because I don't have the feeling that something is being withheld from me or that the mids are falling behind compared to the bass or trebles. On the contrary. The HDXX is a slightly mid-focused headphone, which however harmonizes very well with the bass and treble and is oriented towards a neutral frequency response. The mid/upper bass gives them a bit more warmth, to speak of absolute neutrality, but this makes the mids more musical and gives them a natural sounding timbre. Vocals should be mentioned here as a highlight, but the tonality of instruments is not to be blamed either.

Trebles
In the high frequencies the HD6XX is a bit more reserved than it should be. It sounds absolutely realistic and provides a lot of information, but in the top end it might be a few dB more without making the sound too bright or artificial in my opinion. This could also give the HD6XX more transparency. Here I would like a more direct response, but as in the bass and mids this is criticism on a high level, because basically the HD6XX does everything right when it comes to natural sound reproduction. Only a little bit the effervescence is missing, but life is not a rainbow-colored unicorn and therefore you can't really blame the HD6XX when it tries to stay authentic. Sibilants or peaks I can't make out, which makes for an absolutely safe and fatigue-free sound experience. Tonal correctness is clearly more important for the HD6XX than the big show.

Stage
Thanks to the open construction, the stage has a lot of space in the width, but it is somewhat limited in the vertical. This means that the sound information is displayed in a somewhat compressed form when compared with the AKG K/Q701, for example. However, this gives the HD6XX a pleasant intimacy and it has a robust foundation.

Imaging
When it comes to imaging, the HD6XX doesn't necessarily play over budget, but it plays within it. Due to the somewhat lacking clarity and sharp separation, the HD6XX doesn't have any localization problems, but the space between the individual pieces of information is not the biggest and can collide here and there. Nevertheless, a very coherent 3D image is created, which I find realistic, even though I would like to have a little more space to the top.



Outro
The HD6XX is often considered the best value for money at the moment when it comes to a laidback, neutral sound with a warm touch. This is true, but this characteristic is also a reason why the headphone won't knock people out in rows, because the HD6XX doesn't offer an exciting sound experience. Instead, a very natural one, with slight deficits in stage and imaging, which means grumbling on a high level. The relaxed and somewhat "veiled" sound presentation (typical for SENNHEISER) is certainly not to everyone's taste, but for me the HD6XX sounds just right and sufficiently musical, which it has ahead of many AKG models. In addition, there are no limitations in the audibility, which is a bit at the expense of the expansion at both ends.
Also by its appealing detail rendition, the wearing comfort and the authentic sound, especially in the voice reproduction, it is indeed a value that is hard to top, since the HD6XX is above all a weapon in tonal terms.
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More reviews: CHI-FIEAR
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An oldie but goodie. I reviewed this on my brand new YouTube channel to hopefully establish common points between my listening and a new audience's listening. Enjoy:





Enjoy the music, everyone!

Disclaimer.​

I'd like to thank DROP for sending me the Sennheiser HD6XX for a review. I am not affiliated with the company or any of its sellers and write this review with an unbiased opinion regardless of how the review turns out.

About HD6XX.​

HD6XX was born out of a collaboration between DROP (previously Massdrop) and Sennheiser as a revision to Sennheiser’s highly acclaimed flagship of six years - HD650 (2003 to 2009). With the development of HD6XX, they made some minor aesthetic changes like a deep midnight blue paint job, black nameplates with silver text and Massdrop logo silk-screened inside the headband but tried to keep the original sound of the HD650 intact. Based on feedback from the community, this iteration was also updated with a detachable 6-foot cable (compared to the original’s 10-foot cable) and a 3.5mm plug, which is more versatile for everyday laptop, phone, and DAP use than the standard ¼-inch plug. A ¼-inch adapter is included for those who want it. Like all headphones in Sennheiser’s HD 600 line, HD6XX too can be disassembled by hand to its component parts, all of which can be easily replaced. Many of its parts are interchangeable with others in the series and owners of the HD 6XX can benefit from the rich aftermarket and brain trust of modifications and gear matching.

Links - DROP x Sennheiser HD6XX ($220) | DROP Earpads for HD6XX

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Technical Specifications.​

• Color: Midnight blue
• Transducer principle: Open-back, dynamic driver
• Frequency response: 10 Hz – 41 kHz
• THD: < 0.05%
• Nominal impedance: 300 Ω
• Cable length: 6 ft (1.8 m)
• Connector: ⅛ in (3.5 mm)
• Weight without cable: 9.2 oz (260 g)
• Made in Romania

Included in the box.​

• Sennheiser HD6XX
• 3.5mm cable (6Ft)
• 3.5mm to ¼” adapter
• Manuals and warranty card

Build Quality and Design.​

HD6XX’s body is mostly made of plastic with the headband adjuster being the only metal part in there but is put together very well owing to Sennheiser's manufacturing prowess. I’ve always liked the design of the HD600 range in general and the HD6XX is no different. The midnight blue colour looks almost like black and I’m definitely not complaining. The open back grill and the exposed driver look of the HD6XX is a timeless design, eye catching even today and puts HD6XX up there as one of the best-looking headphones in its price range. The headband adjuster is a bit tighter than I like but in turn works well to keep the headphones firm where you set them without the adjuster dropping down loose on its own. Besides that, I really have no complaints.

Cable – Right up, I’m not a fan of HD6XX’s cable. It’s rubbery, cheap looking and too long! Besides that, it does its job and works. Drop and Sennheiser should definitely put in a better-quality cable, even better if they can offer a nice balanced cable as stock.

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Fit and Comfort.​

The fit for me is pretty good as the headphones are light, the ear pads cover my whole ear and are padded enough for my ear to not touch the driver assembly. The clamp force is slightly on the firmer side right out of the box but there is a popular trick to slightly bend the headband adjuster towards the outside to reduce a bit of the clamp force. The clamp force is fine for me if I’m using the headphones for short durations but I do start feeling it after a while. I might try the headband flexing trick once I get over my fear of breaking them while doing so. Lol!

Sound Analysis.​

Drivability - HD6XX has an impedance rating of 300Ω and needs a bit of juice to be driven to decent levels. I could drive it to a decent level with my Oneplus 7 Pro phone and MacBook Pro laptop by maxing out the volume but it sounded much better with my DAPs and audio interfaces. You should easily be able to drive it through the SE output of your DAP but I highly recommend getting a balanced cable for the HD6XX and using more quality power available from the balanced outputs. Also, it is popularly known to scale even better with good quality desktop gear and good portable dac/amps. I tested the HD6XX mainly with the SE and balanced outputs of Hiby R6 2020 & iBasso DX160 as well as the headphone output of Universal Audio Apollo and Focusrite Clarett 8PreX audio interfaces (while testing and using it for my music production work).



Summary – HD6XX has a very natural, well-balanced, warm sound signature with very good tonality and timbre of instruments. It has a mostly neutral bass presentation except for a minor sub-bass roll-off around 40Hz and a tiny 2-2.5dBs boost in the 80-200Hz range. It has extremely well-done midrange which is its main USP; it being linear, neutral and almost perfectly tonally accurate. Lower treble is natural, easy to listen to without any harshness or sibilance. Upper treble extension is fairly good with a prominent peak at around 15kHz. Overall, HD6XX is one of the easiest headphones to get along with because of how natural, comfortable and well-done the sound signature is.

Let’s dig in deeper…

Bass – HD6XX has a mostly linear and neutral bass presentation. Being an open-back, it comes as no surprise that it has a minor sub-bass roll-off of 1-2 dB slope starting around 35-40Hz but because of it being relatively minor, it plays sub-bass till 20Hz decently, just not with a lot of rumble. It has a tiny bass boost of 2-2.5dBs in the 80-200Hz region which adds a bit of punch and excitement. This boost sometimes adds a tiny bit of bloom in some songs which already have a bass boost in this region but I’d still classify the overall bass presentation as fairly neutral and well done in general. Overall, HD6XX’s bass is tight and has good speed, clarity and note weight. Even though HD6XX is tuned more towards neutral, it presents bass in most songs in a very musical way which generally brings a smile on my face.

Mids – Midrange is what HD6XX does really well, in fact exceptionally well considering its asking price. Lower midrange is very clean, neutral and linear while the upper-midrange has a very natural reference-ish forward presentation with good ear gain and peak presence at 3kHz. It has very accurate tonality and timbre of instruments which makes HD6XX sound very natural and realistic. It is fairly resolving and well-layered, especially for its price.

Treble – HD6XX’s treble is well balanced and more neutral with fresh ear pads but starts becoming smoother and more laid back as the pads start to wear and deplete. So, if you want to keep HD6XX sounding its true self, you'll have to switch out the earpads as soon as you start noticing the treble getting smoother or the earpads showing signs of wear. Lower treble in general is rich and smooth without any harshness or sibilance. It has good upper treble extension till 20kHz with one prominent audible peak presenting itself at around 15kHz but it isn’t the most sizzly, revealing or airy upper treble. As a result, HD6XX makes for a rather nice, musical, warm and comfortable listen but resolves nicely with good detail retrieval. It’s the good kind of neutral warm and not dark by any means (at least in my opinion) and that makes it a good fatigue free headphone for longer listens and long hours of production work.

Soundstage and Imaging - HD6XX has a decent soundstage but isn’t as wide as what you’d unknowingly expect from its open-back design. It is more realistic in the sense that it lets you know that you’re listening to headphones but isn’t intimate or claustrophobic by any means and is bigger than most closed-back headphones I’ve tested in its price range. HD6XX’s imaging isn’t the sharpest or pinpoint precise but has fairly good separation between instruments.

HD6XX for music production.​

HD6XX has very good resolution for its price segment and portrays instruments in the mix with good realism. I’ve used quite a few headphones in my career as a music professional but have always felt confident having a Sennheiser HD600 series headphone around in the past when working on guitar, bass or drum tones because of how naturally and realistically HD600 series headphones are able to recreate the image, tonality and timbre of the instruments with good resolution. HD6XX is no different in this regard and I found myself using the HD6XX more and more for my production work than others. HD6XX isn’t a headphone that boosts treble like crazy for detail retrieval but in fact does it with technical capability and tuning while maintaining a warm and easy sound signature that helps in keeping long production hours and listening sessions fatigue free.

DROP earpad options for HD6XX (link).​

Sheepskin Leather.
Fit - Lesser clamp force, more comfortable.
Sound - Darker, boomier and fuller lower-mids.

Fenestrated Sheepskin.
Fit - Even more comfortable, more breathable, lighter feeling.
Sound - Not as dark sounding as Sheepskin, lesser fullness in lower midrange, slightly more treble than Sheepskin but still darker and boomier than stock ear pads.

Hybrid Velour.
Fit - Very comfortable, much better than stock ear pads.
Sound - Lesser bass slam, midrange is a bit boxier than Fenestrated Sheepskin, smallest soundstage.

Overall, HD6XX sounds best with the stock Velour ear pads. Unless you want to try the other earpads for better comfort, I’d recommend sticking with the stock ear pads for the best tonality and sound signature.

Comparisons.​

I’ve compared the HD6XX to headphones I think are fit for a comparison based on style of tuning and price segment competition, regardless of driver type or style of headphone.

Sennheiser HD560S ($200) – HD560S is another open-back dynamic driver headphone from Sennheiser around HD6XX’s price point, selling for around $200. Build wise, HD560S is all plastic too (except for the metal grill) and is very well put together but I personally dig HD6XX’s design and build a bit more. HD560S has slightly less clamp force compared to HD6XX but I find them almost equally comfortable for my head. HD560S has an impedance rating of 120Ω and is a smidgen easier to drive than HD6XX but not by much. HD560S has better sub-bass extension and is more neutral but HD6XX has better bass punch and upfront definition. HD6XX is a smidgen more neutral and fuller in the 250-500Hz region compared to HD560S which is slightly leaner there but the rest of their midrange character is rather similar besides that. They both have similar linear, neutral lower-midrange and forward upper-midrange with almost similar ear gain but HD50S is a bit more prominent in the 4-5kHz region. HD560S has more lower treble in the 5-9kHz and more upper treble in the 13-20kHz region, making it significantly brighter than HD6XX but isn't abnormally bright or harsh as such. I'd basically classify HD560S' treble as neutral-bright and HD6XX's as neutral-warm. HD560S has a bigger soundstage with more width and depth but HD6XX has slightly better separation, realism and note weight. Also, HD6XX's overall sound signature scales better with more power and better gear than HD560S. Yes, Sennheiser's own HD560S gives HD6XX some good competition but I think HD6XX holds its ground and comes up on top in quite a lot of things. In general, preferences and basic choice of flavour will play a major role in choosing one over the other.



HifiMan Sundara pre-2020 revision (~$350) – Sundara is a planar magnetic open-back headphone with an impedance rating of 37Ω and sensitivity of 97dB. It is fairly easy to drive from most devices but benefits from more power. I’ve included Sundara in the comparison because it too has a fairly neutral tuning and is a headphone enthusiasts generally have on their radar. Sundara has slightly less clamp force than HD6XX but is a bit heavier. Sound wise, Sundara is more a neutral-bright headphone compared to HD6XX's neutral-warm tonality. Sundara rolls-off sub-bass sooner at around 50-60Hz whereas HD6XX rolls-off at 40Hz. Also, HD6XX has a tiny bit more mid-bass presence. As a result, HD6XX has more bass punch and a bit more rumble than Sundara but Sundara has a more neutral mid-bass presentation. Both have linear and neutral lower midrange and forward upper midrange presentation but HD6XX does it more linearly, naturally and organically. Sundara has a dip in the 1-2.5kHz region which makes HD6XX a bit more tonally accurate in the region. Sundara has more presence in the 4-5kHz region and can come off as shouty to some. Sundara has more lower treble and upper treble presence than HD6XX. Simply, Sundara is slightly north of neutral in its treble presentation making it a neutral-bright headphone whereas I consider HD6XX as neutral-warm. HD6XX is more organic, warm and comfortable sounding whereas Sundara has sharper attack and slightly thinner tonality because of its brighter upper-treble tuning. Sundara has the bigger soundstage of the two but I find HD6XX’s overall imaging a bit more natural as a musician/music producer. Sundara has a bit more micro-detail retrieval, a lot owing to its brighter tonality but can be fatiguing for some in longer listens compared to HD6XX.

Ollo S4X (€399) – Both are open-back dynamic driver headphones but S4X has an impedance rating of 32Ω and is much easier to drive. Even though HD6XX’s build is quite good for its price, S4X’s boutique design and build quality seems more premium and attractive. Fit wise, HD6XX is fairly comfortable because of large ear pads that go over the ear properly but the headband can have a stronger clamping force for people with bigger heads. On the other hand, S4X’s auto headband tensioner mechanism and clamping force is more comfortable but the ear pads are smaller and do not engulf the whole ear comfortably. S4X has a much better looking and feeling cable compared to HD6XX. Sound wise, running both through the 4.4mm output of Hiby R6 2020 in low gain, S4X has better sub-bass extension whereas HD6XX rolls of around 40Hz. S4X has a bit more mid-bass and lower midrange body in the 250-600Hz whereas HD6XX is more linear and neutral there. Both do upper-midrange very well but S4X has a bit more note weight and definition owing to a bit more ear gain whereas HD6XX is a bit easier and comfortable sounding. When it comes to lower treble, HD6XX has a minor dip in the 6-10kHz region too but is not as dipped as the S4X and as a result, hi-hats and cymbals are a bit more prominent and better portrayed in the HD6XX than S4X. Both have good upper treble extension but HD6XX becomes more laid back as the ear pads start wearing out but is a bit more prominent in upper treble with fresh ear pads. S4X comes across slightly more even and warmer in upper treble presentation in comparison. Soundstage wise, S4X is slightly wider and deeper as well as has better imaging and layering across its soundstage.

Conclusion.​

Let me put this simply – There is a reason why DROP has sold more than 125,000 units of HD6XX since its release and also why you hear stories of long time enthusiasts falling back to a HD6XX/HD650 after going through several much more expensive headphones. It’s simply because of how well-tuned the HD6XX is. HD650 was regarded as one of the best headphones ever made back when it was Sennheiser’s flagship in the late 2000s and HD6XX still carries that legacy very well even today against the current competition. Yes, it’s not completely devoid of flaws but it does way more things well than it faults. It has one of the best midranges and is one of the most natural sounding of headphones not just in its price segment but even $500 and further. Its treble is resolving but natural and smooth, which makes it a headphone that you can comfortably listen for hours. It doesn’t have a lot of sub-bass rumble but the rest of the bass presentation is quite pleasing in my opinion. It is not the easiest to drive and doesn’t have the widest soundstages of open-backs in its price range but scales even better on good gear and the rest of it is so well executed that it makes it one of the nicest headphones at its price point. All in all, HD6XX presents great value at $220 and is a headphone that is definitely not going to leave my arsenal until it dies on me. I can safely and easily highly recommend it!

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Gear used for testing and review.​

• DAPs – Hiby R6 2020 | iBasso DX160
• Audio Interfaces - Universal Audio Apollo | Focusrite Clarett 8PreX
• Laptop – Apple Macbook Pro 15″
• Phone – OnePlus 7 Pro

Reference Songs list.​

• Foo Fighters – The Pretender, Best of you, Everlong & Sonic Highway album
• Coldplay – Paradise, Up in flames & Everglow + Everyday Life Album
• Biffy Clyro - A Celebration of Endings & Ellipsis albums
• Ed Sheeran – Thinking out loud, Bloodstream & Galway Girl
• Dave Matthews Band – Come Tomorrow album
• Dua Lipa – Future Nostalgia album
• Chainsmokers – Somebody, Sickboy, This Feeling & Closer
• John Mayer – Slow dancing in a burning room, Stop this Train, Say & A Face to Call Home
• Gavin James – Always & Hearts on fire
• Switchfoot – Meant to live & Dare you to move
• Porcupine Tree – Sound of Muzak, Blackest Eyes & .3
• Our Lady Peace – Do You Like It & Innocent
• Linkin Park – Papercut, Somewhere I belong & Talking to myself
• Maroon 5 – She will be loved, Payphone & Lost stars
• Lifehouse – All in all & Come back down
• Breaking Benjamin – Diary of Jane
• Karnivool – Simple boy & Goliath
• Dead Letter Circus – Real you
• I Am Giant – Purple heart, City limits & Transmission
• Muse – Panic station
• James Bay – Hold back the river

Price/Performance: 5 star headphone.

IMPORTANT: BURN IN THE HEADPHONE FOR 24 HOURS.

These have a pretty solid soundstage, much bigger than your typical closed headphone. They definitely excel with any kind of acoustic music. I have also found that they're great headphones for tuning a system because it's very easy to hear changes in the system and make sense of them. Very balanced sound.

They aren't the type that make every type of music sound good. They make most types sound good, but I actually dislike them with most techno music. For one, they don't have the greatest bass of all time, and they're a bit mid bass heavy for most techno tracks.

Some headphones in the price range produce better bass, such as Meze 99 Noir's. But, the HD6XX are in general much more revealing and accurate across the rest of the frequency range than other headphones in this price range.

Once you realize that these headphones are way beyond most USB dac/amp combos you'll appreciate how good they can be. Don't be to quick to judge these headphones as they're very transparent and reveal every little miscue in your setup.

I bought HD 6xx in Nov 2016. Before I got this, I already got ATH AD1000x, ATH M50x, and Massdrop X AKG K7xx. So I will compare HD 6xx to these three headphones.

Appearance and package:
The package is way better than Massdreop x AKG K7xx. There is a nice box and soft sponges. On the top of the headphone, there is a beautiful Sennheiser logo. Wire is detachable. I know there is some upgrade wires for this but I didn't buy it.


Comfortableness:
It is quite comfortable when I put it over my head and ear. It covered all over my ears and the soft velvet(?) is pretty comfortable. It is a little bit tight but not as tight as M50x. I won't feel uncomfortable for several hours. Compared to ATH AD1000x and AKG K7xx, it is tighter than those two.

I have run for more than 100 hours since I got this.

Sound:
The sound is clear and beautiful!
The Music style I usually listen are classical music, Japanese Pop and female singers, such as Beyonce and Celine Dion.
The voice of violin are bright. The sound stage for symphony are excellent. The dumb and cello are thick and firm. It also preforms great in low frequency.
The female singers voice was crystal clear and bright! The sound stage are deep and broad.
Male singers, like Josh Gorban, are also good.