Sennheiser HD660S2 Measurements: The Clone Wars

Discussion in 'Headphones' started by purr1n, Mar 1, 2024.

  1. purr1n

    purr1n Desire for betterer is endless.

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    Subjective impressions and other measurements here in this thread: https://www.superbestaudiofriends.o...on-to-be-controversial-hd-660s2-thread.13205/

    Sennheiser HD660S2 (New Pads)
    Frequency Response
    (compensated to DF 1/db downward slope)
    upload_2024-3-1_9-14-6.png

    Let's compare to HD650 and JAR600 below. Measurements are mostly consistent with my concise subjective impressions here: https://www.superbestaudiofriends.o...sial-hd-660s2-thread.13205/page-4#post-425945. A summary:

    • HD600S2 is more full bodied (or has less bass hump depending how we want to look at it)
    • HD600S2 is recessed in upper mids
    • The funky thing that I mentioned (subjective): HD600S2 has more edge or is more prickly than either JAR600/HD650. The measurements show HD660S2 to have less treble overall from 7-10kHz, but why is this? Could be be the 5.5kHz peak? Let's look at CSD and Burst Attack Envelope later...
    • Measurements alone would suggest that the JAR600 would be more difficult in the highs than the HD660S because the JAR600 has a bump around 8kHz, but I actually found the JAR600 to be more even sounding, less prickly, less edgy, than the HD600S2.
    Sennheiser HD660S2 -vs- HD650 (WHT)
    Frequency Response
    (compensated to DF 1/db downward slope)
    upload_2024-3-1_9-14-35.png

    Sennheiser HD660S2 -vs- JAR600 (WHT)
    Frequency Response
    (compensated to DF 1/db downward slope)
    upload_2024-3-1_9-16-33.png
     
  2. Serious

    Serious Inquisitive Frequency Response Plot

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    I fully expect the 5kHz peak to be a resonance / ridge in the CSDs with resulting overshoot and ringing in the burst response.

    Does it sound smoother than the old HD660S? Comparing against a JAR600 is maybe a bit unfair. Is it smoother than a stock HD600 from memory?

    Still looks like it has those HD700 driver type issues. Hopefully less bass distortion this time around.
     
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  3. purr1n

    purr1n Desire for betterer is endless.

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    From a tonal signature and transient response perspective, the HD660S2 sound worse! I actually like the tonal response of the HD660S (just a bit of 2kHz weirdness, but minor complaint really).

    upload_2024-3-2_10-28-56.png

    ^ The 4800Hz attack envelope is probably explains what I did not like about it: edge and prickliness. It's not a pleasing pattern based on available data. Will explain a bit more down below.

    Here is the HD660S (OG)
    upload_2024-3-2_10-31-51.png

    LCD#2
    upload_2024-3-2_10-32-13.png
     
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  4. purr1n

    purr1n Desire for betterer is endless.

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    Naturally burst attack envelope will not explain everything (it's important look at FR, CSD, distortion, and many others to get a more complete picture). However, I thought I should offer these comparisons.

    I think the overall smoothness - the more gradual rise and descent) of the burst amplitude in the HD600S and HD600S2 (to a lesser extent) do make them less annoying (in the highs / transients) than the HD700's transient attack behavior, which is more sudden.

    hd660s2trans.jpg
     
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  5. purr1n

    purr1n Desire for betterer is endless.

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    They need Axel Grell back. They need to get their shit together. Sennheiser could have come up with a proper e-stat solution that offered better flexibility. They could have done so and priced it at $7k and sold thousands of them. Instead they decided to go full stupid and make a 911 GT3RS (which BTW no one gets at MSRP, unless they've purchased $1M worth or Porsches at a local dealer). Talking about the HE-1 system made of marble. Heck, they could have just re-released the HE90 which was a better e-stat headphone than the HE-1.
     
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  6. purr1n

    purr1n Desire for betterer is endless.

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    HD660S2 L
    CSD
    upload_2024-3-2_10-54-32.png

    HD660S2 R
    CSD
    upload_2024-3-2_10-51-50.png
     
  7. Lyander

    Lyander Official SBAF Equitable Empathizer

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    It's actually impressive how it's got MORE edge than the RS2 with TTVJ pads. The HD660S2 has a WAY higher peak at 4800Hz and persists for longer before beginning to settle, like damn:

    [​IMG]

    The 6kHz doesn't ring nearly as much as expected, but yeah that still looks rough. I don't think you've shared CSDs of the HD600 or HD650 (either stock or modded) where it goes down to 20Hz like with the more recent CSDs, or maybe I just missed them? Would be curious to see if the low end gets "filled in" too, which would imply perceived bass could be greater than FR implies.
     
  8. Grattle

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    I do not have the time spent with an HD650 modded or not. I’ve spent even less with the HD600. I’ve spent somewhat more now with the 660S2, and I really enjoy it. I feel like that going from my poor memory, that it does everything the stock Senns do, but better. Maybe the mods make the difference. With the caveat that I got mine from Sweetwater for $399, I’m going to say that out of the box, they are the best of the 600 series. Just my opinion. I listen to mine on an OG BF2 with a SW51+.

    Edit: Any newbs reading, @purr1n knows far, far more than I about these headphones so bear that in mind.
     
    Last edited: Mar 3, 2024
  9. purr1n

    purr1n Desire for betterer is endless.

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    It's where the peak lies. A sharp peak at the first line I don't find annoying. Any sort of bump that lasts on the second line is where I find the highs glarely, prickly, or edgey to varying extent.
     
  10. purr1n

    purr1n Desire for betterer is endless.

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    Very nice distortion characteristics though with the driver - to dynamic driver standards. Second harmonic > third harmonic which is nice, increasing at higher SPL in the lows.

    HD660S2 Distortion Surface - Second Harmonic
    upload_2024-3-8_10-56-5.png

    HD660S2 Distortion Surface - Third Harmonic
    upload_2024-3-8_10-56-50.png
     
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  11. Lyander

    Lyander Official SBAF Equitable Empathizer

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    This actually is kinda surprisingly good, not sure what else I was expecting given Sennheiser's recent track record for measurements-riding. Nothing in the crapfactor area worthy of note?
     
  12. purr1n

    purr1n Desire for betterer is endless.

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    D4 below, rest of crap factor, that is higher harmonics are clean and not worth showing. Typical Sennheiser, they good at this.

    upload_2024-3-8_11-22-53.png
     
  13. chesebert

    chesebert Friend

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    “The funky thing that I mentioned (subjective): HD600S2 has more edge or is more prickly than either”

    This was my experience as well. Unit variation helps to a certain extent. I had 2 660S2 and 1 was nicer/lesser annoying than the other, which sounded like auto tune on steroids with female vocals.
     
  14. Lyander

    Lyander Official SBAF Equitable Empathizer

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    Curious that there's that much variance among Senn headphones, but makes sense I think since even the HD800 line was subject to the same. Same pads used between units, and same chains?
     
  15. chesebert

    chesebert Friend

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    Both new units and same chain. Unit variation is not anything new with cans.
     
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  16. kman1211

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    Thanks for these measurements, I was wondering why the headphone sounded like it had such an edge to it’s treble despite being quite dark sounding to my ears. I think it sounds a bit artificial in the vocals, it was fun to listen to at first but starting to have mixed feelings about the S2, they didn't go the right direction from the S1. My HD 600 and HD 650 are much better than it in terms of vocal reproduction. My Beyer T1.3 has better and more organic vocal reproduction as well despite its unconventional tuning.
     
    Last edited: Mar 21, 2024
  17. Lyander

    Lyander Official SBAF Equitable Empathizer

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    The HD660S2 is very much overpriced. That said, it's really not all that bad technicalities-and-voicing-wise even though there are some definite shortcomings espectially in the treble presentation.

    In my country it used to retail for the equivalent of $820, and even now the current Philippine MSRP of Php 41,390 translates to about $710 at current exchange rates. I know that tariffs are a massive pain in the butt but this is ridiculous; at this price point, folks are best going to be served by hunting for used HD600s or HD6XXes (or HD650s even, though given the existence of the 6XX that one's got a bit of a questionable value proposition now I think).

    Looking over at Amazon USA, I think the $400 you can get these for right now sort of makes sense even considering that's a price match for a modern production HD650, not to mention it's significantly more than the $320 the a new HD600 costs and completely ignoring that you guys can still get an HD6XX off Drop for $199.



    The analogy I immediately came up with when I first got ears on the HD660S2 is that, relative to my later-production marbled HD600, it sounds like how a pretty damned good digital camera looks-- compared to that the marbled HD600 is in this analogy a shockingly good film camera. Both are good headphones overall and each has specific advantages over the other. Maybe I'll lean more towards one or the other with a higher-tier rig, but right now out of mainly a Modi Multibit 2 and a Magni Piety (with occasional chiming in from a Magni Unity or MCTH) I feel both are of equal standing, albeit in different aspects.

    The HD600 has richer note weight and just a better sense of back-to-front layering that sort of comes part and parcel with a more intimate headstage, not to mention things just sound more "correct" on it timbre-wise. This still holds true even after forcing myself to stick with the HD660S2 for multiple weeks before jumping back to the HD600s-- I only need a very brief reacclimation period for my ears to recognise how much more "right" things sound on the older Senns (mainly necessary due to how different the upper mids presentation on the two are).

    Where the HD660S2 does excel and surpass the older Sennheiser is in headstage size, imaging, and just an overall sense of litheness to things-- it's a faster-sounding headphone in the same way something like a Focal Clear sounds "faster" than the HD600, maybe something to do with how it's just a drier sort of presentation. It's nowhere near being as reactive-sounding as a Focal nor does it come across as ethereal and immaterial as lots of HiFiMAN headphones do (n.b. I still haven't heard a *properly* amped HiFiMAN I think), but it's a step towards that from the HD600s.

    The dBel-modded Yamaha YH-100s I have present a more "there" headstage with things having a greater sense of outwards presence-- as much as those aren't quite perfect headphones for me, it's always uncanny how much I feel like I'm being tricked into hearing stuff as going on from outside those headphones.

    Weirdly enough I do think that for whatever reason the HD600 beats the HD660S2 in low bass pitch differentiation-- on e.g. Daft Punk's Doin' It Right I struggled a bit more to differentiate exactly how deep each bass drop was, though I was able to tell how each note fell relative to the one preceding it. I wouldn't quite call it one-note bass, but it is pretty surprising how much better the HD600 is in this respect even out of an entry-level rig. It is faster-feeling bass than you'd get on the older Sennheiser though-- the quick-fire thuds on Mitski's Happy linger for longer on the HD600s which may or may not be to your preferences. The HD660S2 isn't quite as reticent in slam as the Klipsch HP-3 was, but it doesn't really throw its hips into each punch.

    The more outward-projecting headstage on the HD660S2 is very much evident both for better and for worse. I totally missed that whatever weird TCHK-ing percussion in the intro of Hayley Williams's Sugar on the Rim was supposed to be making a circle in front of me on the HD600s-- it took moving to the HD660S2 to twig onto that, and that's a track I've been listening to for a few years now.

    Funnily enough, off Pure Love on the same album you can easily get a sense for how close to the mic Hayley Williams is during the verses before the stage opens up dramatically during the chorus on the HD600s-- you still get that sense of proximity on the HD660S2, but the contrast is far less pronounced.

    Edge in microdynamics as in really nuanced plucked strings on Rivellon off the Divinity: Original Sin 2 OST or the Mind Flayer Theme off Baldur's Gate 3 go to the HD600, but I'm splitting hairs there I think. They're just slightly less felt on the HD660S2, but when listening for it things aren't really smothered or compressed upwards per se, as they were on the old Klipsch headphones. I feel like even the YH-100s eke out a win over the HD660S2s here, but that could just be because the Yamaha's more delicate (for lack of a better word) overall presentation relative to the Senns emphasises trailing decays and such.

    On the less delicate end of things, RATM's Renegades of Funk kicks ludicrous amounts of butt. The greater low-bass extension is very much felt here, but so is the more aggressive "modern" sense that I alluded to earlier on. Lots of folks have mentioned that despite FR measurements saying elsewise the upper octaves on the HD660S2 sounded oddly grating and harsh, and this is something that I can second. The greater efficiency of the 660S2s doesn't help its case much either when I'm on the Piety as I often find myself struggling to settle on a comfortable volume past the channel imbalance on the Piety's potentiometer, whereas that isn't a problem at all on the HD600s.

    The sibilance and fricatives in a lot of songs e.g. Panic! At the Disco's Emperor's New Clothes are fairly cutting on the HD660S2s, and it didn't actually take me too long to realise that I've been subconsciously gravitating towards less aggressive music while on the newer Sennheisers. Nightwish's Endlessness, which is a hell of a grand-sounding track that just grabs you by the whole torso and drags you along, but it's crafted in such a way that any roughness or unrefinement to the upper octaves stands out and grates on your nerves-- the HD600 is much preferable to the younger sibling with that song. This remains the case for a lot of livelier, less politely crafted J-Pop/Rock like Ado's Buriki no Dance or Rebellion, though I have to concede that the greater bass presence on the HD660S2 masks some of that lack of refinement with music like this, making it palatable enough for me even though you can just tell it's rough up top (Buriki is still pushing my tolerances though).

    With regard to amp pairings, all with the Modi Multibit 2 as a DAC cuz that's the only discrete DAC I have on hand, I mainly really liked the HD660S2s with the Magni Unity since it accented the more modern sound of the newer Sennheisers in a complementary way, and the smoother treble was a GREAT boon especially on very sizzly pieces like Korn - Twisted Transistor which was really close to being eardeath on the Piety.

    I got to borrow a friend's ZDT Jr. again with some aftermarket tubes but I actually disliked the 660S2s out of that one and spent most of my time listening to that amp with the HD600s. I'll get around to sharing this eventually but I did measure the ZDT Jr. as resulting in higher distortion throughout the whole frequency range at the transducer level-- I get the feeling that the higher D3 I was getting in the mids contributed to how, despite the stereotypical TOOB BLOOM the ZDT Jr. is known for, exacerbated the harsh sense I get on the HD660S2s.

    The Massdrop Cavalli Tube Hybrid remains a very cosy and pretty sounding amplifier to me, but I didn't feel it was a good match with the newer Sennheiser. The bass on e.g. Evanescence's Sick and End of the Dream off their third album was less distinct, felt more than heard, and I struggled to set a level where the vocals weren't buried but also not glaringly painful. The spatial elements of the presentation were great, but I just found myself much preferring the HD600s out of this amp too.

    I got more than enough volume out of the FiiO BTR7, be it out of the SE or Balanced outputs, and I have to say that the more relaxed transient presentation of the dongle did sort of help the HD660S2 be less painful to listen to, even though the lack of treble refinement remained very evident.

    I'm also well aware that the Modi MB2 is far from being the most refined DAC in terms of treble response so there's a pretty good chance a lot of my complaints aren't going to translate to lots of other folks' experiences, but it is what it is.

    Having said that though, I did try the HD660S2 with the very worn out pads on my HD600s and really liked what I was hearing. Even now with the pads the 600S2s came with compressing slightly from frequent use, I feel like the harshness is *somewhat* ameliorated. Kinda hopeful that this might result in an actually not-terrible treble presentation... eventually?

    Here's FR of the HD660S2 on the MiniDSP EARS versus the HD600. To minimise variables, I used the same pads between them. I don't fully trust the MiniDSP squiggles but they do a decent enough job showcasing relative differences I think:
    [​IMG]

    And here's left and right of the HD660S2 as of a few hours ago. I feel like lots of the variation here is down to asymmetric pad wear because when I took measurements without pads things were more tightly matched, but overall things sound closely matched enough that I can tell when things are skewed one way or the other.
    [​IMG]

    And lastly, here's how the HD660S2s measure with newish pads (BLUE trace), slightly broken-in pads (RED trace), and with the very nearly disintegrated ancient pads I've been using with my HD600s (YELLOW trace). I see things sort of smoothing out up top which makes me think that these could grow to be much more palatable-sounding over time.
    [​IMG]

    Distortion here is just about what you'd expect: nothing of note above my noise floor except for a bit of a D2 rise in the bass. Eyeballing distortion vs the HD600, doubtful as I am about how useful this'd be given my location is far from quiet enough even in the dead of night, they look exactly the same.
    [​IMG]

    The CSDs of the HD660S2 are clean enough below the middle midrange but I can see hints of the lower treble ringing Marv caught above. The MiniDSP EARS rig won't be the best for CSDs because of the weird Pringles can ear canal, but..,
    [​IMG]

    Amusingly enough when you swap in the really old HD600 pads I have, you can more readily see the ringing Marv was getting on his flat plate coupler. I guess more directly interfacing with the measurement mic has its benefits. Who'da thunk? Genuinely curious how a significantly more expensive HATS would compare here.
    [​IMG]

    I do know that IR is essentially just another way to view FR (took me long enough to remember lots of other folks saying as much) but I do wonder at whether this could explain at least in part why I hear the HD660S2 as sounding "faster" (even though you can see the HD600 actually has less time between peaks-- could that be related to the sense of greater note weight?)
    [​IMG]

    I did a quick visual inspection of the newer (~2019) HD600 capsule assemblies against an older (~2014) pair some time ago and a lot of my comments about how much less finished the newer HD600 looked apply here too: the fit and finish of the HD660S2 seems like it was held to a lower standard than the older Sennheisers (pictures to follow when I'm less lazy). Heck, even though they're advertised as having the same weight as the older Sennheisers I just feel like the marbled HD600s feel more premium, like they've got a bit more heft to them and are made from nicer plastics (fountain pen nerds will know what I'm talking about).

    I busted out the coffee scale and was surprised to find that, yeah, the older HD600 actually weighed about 12g more than the HD660S2 (271.8g vs 258.8g). Granted a fair part of that COULD be dead skin cells and Lord knows what else, but I feel like the sublimation of lots of the pad material ought have compensated for that; it just FEELS more premium than the newer HD660S2, though I can't say that less weight on the neck isn't appreciated.
    [​IMG] [​IMG]

    Okay, that's all I have energy-wise. I meant to only write brief comments but ended up doing my usual rambling review anyway. Fun.
     
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    Last edited: Jan 9, 2025
  18. Grattle

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    This is a fantastic analogy. I have the 660S2 and have been looking to borrow a 600 to compare it to. Maybe your fantastic writeup will save me that experience...
     
  19. Lyander

    Lyander Official SBAF Equitable Empathizer

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    I do kinda feel that they'd be complementary to one another depending on what sort of upstream you have. You can tell that they're part of the same family just going off how they sound, sorta, but the HD600 is a person in middle years who is comfortable with their shortcomings and because of that is self-assured in how they conduct themselves whereas the HD660S2 is someone of similar age who hasn't quite made peace with themselves yet so tries hard to impress, fumbling some things in the process.

    Both really are good headphones in their own ways and I can see folks liking either of them. The only reason I'm annoyed by the HD660S2 is that it's asking for way too much money in the current landscape, esp. outside of the USA I think-- immediate disqualification just based on MSRP.
     
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  20. Ash1412

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    I've had the HD660S2 and HD600 on trial for a while now. I got HD660S2 for $499 CAD and HD600 for $379 CAD, so in North America HD660S2 is kind on super deep discount during this time of year, probably to clear out stock cause ain't no way it selling at MSRP. Your impressions match 90% of how I hear it and you got measurements to back it up so don't worry about rambling. Now that I see that, I will write down my rant on it too.

    Physically speaking, the HD660S2's only differences from the HD600 are the extra QC sheet, the included 4.4mm balanced cables and different looking drivers. But philosophically they are quite different headphones.

    That metal mesh damping behind the driver makes a huge difference to the sound, and according to Axel Grell himself was adopted by Sennheiser to improve tolerances (48 minutes in):

    I would bet that even though the HD6xx line already has incredible driver pair matching, this mesh damping scheme probably makes tolerances so low you can just replace one capsule if it goes kaput and still have better matching than most other manufacturers' out of the box. And that is what they're flexing with that QC sheet that HD600 box doesn't have.
    => Pro

    And here's their HD660S2 marketing video showing a close up of the stainless steel mesh pieces. They're cool to see in person but I don't have a macro camera to capture it:
    [​IMG]
    This rigid but permeable damping scheme combined with that new lower resonance driver and 4.4mm balanced cable means the HD660S2 is asking to be powered by balanced solid state gear, no question about it. And when it is tightly driven, you can very easily hear the huge difference in bass stability compared to HD600 and HD650 which will just let bass notes smother the ones following it. The distortion numbers might look similar to HD600 but that's more because the HD600 bass is genuinely limp by comparison, while HD650 bass is boomy as shit. The 660S2 will kick hard and then stop on a dime and to me is just generally a lot punchier than the predecessors, more than reviewers who measurebate over pure FR bass extension give it credit for. The HD660S2 damping scheme is pretty much adding ABS braking to the HD6xx driver. This better pressurization of the driver chamber also makes it sound more like the entire driver baffle is vibrating together, so it makes the driver sound much bigger than HD600 in terms of scale. Overall, it's a very modern ass kicking kinda sound and I have to give kudos to Sennheiser for making the most full-range sounding HD6xx phones.
    => Pro

    But there seems to be something with this mesh baffle near the driver that just creates resonances and interference in the treble range. I think @ext1 has mentioned this in passing and it's a big part of the JAR800 mods it seems dealing with this driver-adjacent damping Sennheiser did that's hard to mod around. This really harms imaging/layering and is where I pedantically disagree with @ChaChaRealSmooth and @Lyander. It doesn't sound more open to me if I define open as free flowing treble. I can pick up that it has much better controlled macrodynamics in general versus HD600 and HD650 but that upper range somehow sounds smothered and a bit grating at the same time. And this goes back to the solid state push by Sennheiser: HD660S2 doesn't sound good with SW51, straight up. SW51's bad bass and 54Ohm does nothing to bring out the 660S2's macrodynamics and 660S2's smothered treble does nothing to bring out the SW51's resolve. I used the 4.4mm cable with my ZX300 DAP and it genuinely sounds much better with 660S2 than my BF2OG>SW51 rig. HD600 is the one that has very truthful open treble if a bit bright but it's quite evenly bright throughout instead of being hashy and it absolutely scales more and has much better imaging and resolve, especially with my preferred ZMF lambskin perf pads. 660S2 sounds large and impressive but it does have a bit of a flat diffuse center image thing that @ChaChaRealSmooth pointed out and I can pick up on, while HD600 sounds small exactly like its bottlecap driver size but with ZMF pads and the proper chain can pull out some WTF imaging and depth. Seriously, if you live in the US, HD600 and ZMF pads comes out about the same as HD660S2 and scales better if you're doing source/amp first.
    => Con

    What really pisses me off is why the price of HD660S2 should be that much higher than the other two given that their driver assembly process is more automated by Sennheiser's own words:

    Where's the better build quality that justifies this? Why does the headband still clamp like a vice and squeak? Even at $499 CAD which is $350 USD it feels a bit offensive to get something built like that. The HD6xx was considered well built about 15 years ago back when the rest of the market was doing disposable make and Sennheiser sold official replacement pads and drivers. High quality plastics and replacement pads are completely expected now for premium headphones, and HD660S2 still has the squeaky plastic headband and uber-expensive replacement pads. And I don't even see capsules listed at https://spares.sennheiser-hearing.com/catalog/product/700240-hd-660s2, so does that mean if a driver goes I'm done for or I have to pray for Sennheiser to start selling the capsule?
    => Con

    Personally, I'll repeat what I said before in a profile post: Sennheiser still has the engineering chops but their tastemakers of old are gone and their engineering goals aren't in alignment with what SBAF likes, and that's a bit sad. It feels to me like they gave up on nuanced timbre for tolerance and blockbuster bass. If you're a Jot 2 kinda person or THX789 where the only thing that matters is dynamics and control then yeah it most likely sounds best among the 6xx lineup but if you want authentic timbre just do HD600 and ZMF pads. Depending on system synergy, the HD660S2 is either the Aliens or the Gladiator 2 of headphone sequels.
     
    Last edited: Jan 10, 2025

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