The soon-to-be-controversial HD 660S2 thread

This is really sad, the 6X0 is legendary for good reason, we all know that, but it's 30 years old. They could presumably make a 6X0 with 800ish technicalities, bc we already know it's possible: the JAR6X0B bridges that gap, more or less, by opening up the 42mm dynamic drivers to their full potential. It's the 700 we were hoping for, but never got.

They could also make a better 800, not an 800S2, but an 850 that's not just a retuning like the 8XX or trying to make a closed back like the mess that was the 820.

And then for the 900, they could go beyond the 800 entirely some sort of revival of the baby Orpheus, an eStat tech-based hp (HE900?) that fits in the modern summit-fi category of pricing, next to Susvara at ~6K MSRP. It would actually sell, rather than the statement piece that is the HE-1. Or just bring back the HE90, even.

There's so many possibilities—it's insane—but like you said, they seem, unfortunately for us, to be on some other shit.

I will buy a 660S2, hm, let's see... never. Not in a world where @ext1's remarkable mind and expert hand exists. Nu uh, no thanks.

 

Looks like it. still just the 4 little living-hinge snap-fit prongs holding the capsule to the baffle.

 

Would anyone who has a 660v2 be so kind as to run a frequency sweep on it to see if that big 4.5k dip is real? FR wise from the graph that was the biggest "flaw" I could see. Looks narrow enough that it wont be a big deal during listening, but given the price gotta nitpick it.

Th other obvious complaint is just how cheap the packaging is. You no longer get the nice presentation case or a hard case of any kind, its just a pouch. I guess it is nice from a sustainability standpoint but feels more like a cost cutting measure than saving the environment.

It has nearly sold out in Japan interestingly enough. Surprising considering how much they are charging here (cheapest is about 644 usd).

 

Let me take that on for you. Will put it through the wringer and compare against 650K and whatever measurements of JAR headphones I have.

EARS + flat-plate measurements incoming...

 

First impression: holy moly clampy Batman!
Second impression: I actually don't "dislike" it

Usually I don't show measurements first but... this one kinda warrants it, I guess... since everyone already knows how 660S sounds like and this is basically that. Just... different.



Left and Right with the usual scale...



Note: yes, I tried shifting measurements to make sure that difference in the treble isn't just weird positioning. In reality, I kinda don't hear it but it does show up in EARS.

Against 650 KISSed


580...



P.S.: so yeah, it is what it is. Subjective? Let me live with it maybe for... 48 hours.

Oh, and before I forget: JAR600 (sorry, had to apply 1/48 smoothing to that FR of the JAR due to noise)



If I recall correctly, I remember thinking JAR600 was the best of the bunch or something like that.

 

100% with you here, it;s pretty close to the border for me. Longest session has been hour and a half for me, felt close to pain but not quite there.

Cans are loosening up, not picking up changes yet. Still stand by my feeling that the 650 veil feels lifted here.

 

Still not ready for subjective impressions but... I dug a little deeper.





It's probably pretty obvious which pad is which. The effect is quite interesting when pad-swapping between 660S2 and 580.

Edit: measured:



And yes, subjectively, this did make the headphone brighter to me. Ordering new pads to try since a well-worn pair is probably not very representative.

Left and Right with the usual 100dB scale now with new pads... and I swapped the foam out for something much more permeable:



Very tempted to post something here but I'll again restrain myself for a few days. The pad swap really does change things up quite a bit.

 

Switched to Mjolnir 2 in the afternoon, which is my reference. I think by now the cans are sufficiently burned in. Happy to share there is no fatigue. Definitely V shaped as already mentioned (which is fun), but unlike the Focal Clear, they seem to do well with the expected "fun" of the V and still remain competent in the vocal range (for reference, the Clear sound congested in the middle to me, and too bright).

I remain impressed with the bass (Try the Let It Be 2021 Mix on for size, you'll notice better performance than the 650). It's really good. I don't think these cans are transformative, but they do stand out with their own opinion in the 600 series. Feels to me we now have three flavors to choose from: Neutral (600), Warm (650), and Fun (660S2).

For those with Vulcan ears: do you share my impression about the veil being gone? (I think the energy at the edges and the speed is what creates the effect for me).

Leaning towards keeping at the moment...

 

I’ve had these for a little bit now and have been directly comparing to the HD 600, and yeah they’re definitely not a definitive upgrade. I tend to eq them both to a very similar target so my impressions are mostly focused on the more supjective/technical aspect.

Relative to the 600’s, the 660S2 portray a better sense of macrodynamics and the transients are faster and more clearly defined, but the 660S2 aren’t as profficient in the detail within the trailing ends of tones and the decay of stringed instruments isn’t as natural sounding IMO. Treble is ‘sweeter(?)’ sounding on the 600. I find the biggest difference to be in the bass whereby the 660S2 is better controlled and tighter. Headstage is similar enough that it shouldn’t be considered in a purchase between these headphones, perhaps the 660S2 is a hair less 3-blobby but the difference is very slight, however I find the image seperation to be a bit better on the 660S2.

I do think the 660S2 is noticeably less grainy and coarse sounding than the 660S version 1 which is a nice improvement but if the 600 and 660S2 were at the same price I’d still pick the 600 six out of seven days of the week.

 

Okay... well, it's been 2 days. I put the headphone through everything... including trying to do simple front filter mods and pad mods. Here are my impressions.

Let's first look at packaging:



Who the f... thought it would be cool to pack the headphone like this??





So in short, I've bought $199 headphones that have more premium packaging than this. And no, it's not even just the HD6XX from Drop but like... even something like a random Beyerdynamic headphone around that price point or even cheaper on sale typically comes with a massive carrying case. Not just a pouch. Hell, I bought a Koss PortaPro for $50 that I'm pretty sure... was packed basically like this. At least... they included a 4.4mm cable as well that... honestly, I don't use. Does anybody even??

Comfort out of the box for this is still... disastrous. Not much more to say here. Going back to a well-worn and well-bent pair of HD580 is like... an insane difference. Hell, even going back to a well-adjusted HE-6SE is a whole other level of revelation and comfort. And HE-6SE should be almost twice the weight!

As for sound, on first listen, I can hear where this is pulling ahead of my 580 and 650. Bass is indeed cleaner and does extend further. Treble is smoother and kind of slightly more airy than 650. Midrange is indeed showing a bit more spatial cues that 580 and 650 sometimes would gloss over. Is it all rosy then? Nope.

The bad thing is... the FR IMHO is just not a good fit with this driver. It highly reminds me of that time I owned the stock LCD-2. Which may... not be that bad but then it's a dynamic headphone. It's lacking that planar slam and the weight and impact and clarity of "dat bass". So it doesn't quite excel there, and it doesn't quite excel up top either. I can hear that it's trying to be brighter than 650 but it can't quite reach that. Missing the region between 2-4KHz is not doing this headphone any favors. In most cases, both my 580 and 650 win the "tone" battle by a landslide. It's not even a close contest. Female vocals soar well past the building with 580 and 650, but 660S2 just can't quite even get to the 1st floor of that same building. It's kind of crazy but on some tracks, 660S2 sounds cleaner than 650, but then immediately on the next track it can sound more muted (almost more muddy) than 650 due to lacking upper midrange. Putting 580 on, the sound makes it feel like I just came out to the sun after 1000 years underground.

And beyond the FR, the driver just isn't that capable. If I hadn't tried to shove a HD800 into similarly-sized housing, I would have attributed the sound to the housing. But no... it's most likely just the driver. There's something sluggish about this driver. It reaches low and it's pretty clean-sounding with bass but it's just not "fast" enough? Going from this to even something like HD580 is a "revelation". HD580 just sounds so much faster and more airy despite FR telling me 660S2 should be the brighter headphone or at least equivalent in brightness. Let's say that it basically doesn't sound like how it measures and is actually even darker.

Granted, I can see what this one excels at: if anyone owns a vast collection of marginally-recorded songs, this is probably the headphone for that. It's like someone dialed the EQ down to make absolutely sure that even intentional sibilance is completely gone. The treble is so "chill" that going back to my speakers almost hurts my ears once my mind acclimated to the sound. I can almost tell whoever approved the sound of this headphone is probably super young and is super sensitive to the region above 3KHz, and the only reason why that peak at 8KHz was approved was maybe because it was unavoidable (660S also seems to have the same peak).

So is it a bad headphone? I honestly don't think it is that bad. A few tweaks show me at least someone spent time engineering a better solution than 660S. But... it's just not enough.

I think... this might make more sense around $199 or hell $299 after adjusting for inflation. It looks like they're trying to go after 650 here. Makes sense it's an alternative to 650. But at $599??? Even for a Sennheiser fanboi like me, that's... too rich for my blood.

Old Sennheiser is gone. Long live the King!

 

I haven't seen people mention this yet but yeah, the treble is a teeny tiny bit on the hot side for me as well, otherwise I really like the tuning here. There's this sweet, warm, comfy yet detailed sound with a little sparkle up top and some tight and thumpy bass performance.

The last time I heard a 6xx series headphone (HD 650) was years ago, this seems like a nice modern alternative to the HD 650, the pricing however is definitely taken a bit too far, $600 for a flimsy box, baggie, cables and the headphone.

 

Looks like I'll keep my HD650 and Silver Dragon cables a bit longer!

 

Sennheiser 660s2 Review
​

Chain: PC USB Out --> Bifrost 2 (Vanilla) --> Elekit TU-8600s | SW51+ Schiit Fulla (PC --> USB)

Headphones:

Sennheiser 650 | 660S2
Focal Elex
ZMF Verite Open



Build/Packaging: If you’ve touched a 600 or 650 then you’re familiar with the build. As others have mentioned concerning the packaging, it’s…very lackluster. Usually, I would care less what packaging the headphones come in as long as the headphone sounds great. A great example is the LCD-2 Classic; it comes in a brown box but for $800 you’re getting a solid well-built headphone.

Headphone Impedance Caveat: I had to be aware that I couldn’t just say, “Let’s test this on the SW51+ and call it a day”. The difference in the Z-out matters and how it changes the frequency response for that specific headphone. It won’t do the Elex justice connected to the TU-8600s as the impedance is too high. It’ll make it sound sloppy, but it also won’t do the 660s2 justice running it off a low z-out. My comparisons will be with the Elex on the SW51+ (low z-out) and the Schiit Fulla; with the Sennheiser 660s2 running out of the TU-8600s.



Sound:

Attack: Both the Elex and 660s2 have sharper and snappier attack than the 650s. If you found issue with the 650s blunting certain instruments (snares, percussion, hi-hats, etc..) then you’ll enjoy that it’s moving slightly towards something like the HD800s, Auteur, Atrium levels. Still, even with it slightly moving in that direction I still find them forgiving. If that’s a good thing or bad thing I’m not sure. Listening to Steely Dan’s – Jack of Speed, I know for certain that the snares have a livelier feeling on the Auteurs than the 660s2.



Imaging/Headstage: The 660s2 images are slightly bigger and taller while the Elex, believe it or not, displays a wider and deeper sound stage than the 660s2. Really, I never think of the Elex as having a big head stage but when I put them on, I thought, “Finally, some damn room to breathe”. The 660s2 improves on the 650s head stage (more rounded and slightly deeper) but instruments feel like they’re close to each other. Now when it comes to delineation, the 660s2 takes the cake compared to the 650. You don’t have a fuzzy outline to instruments and feel more solid.

Speed: This is something that is a much-enjoyed improvement to my ears in comparison to the 650s. The 660s2 is a much faster headphone than the 650 with better separation. The headphone has a much easier time with Trampled by Turtles – Wait so Long than the 650 but the Elex still does a better job. I’m not sure if it’s because of the frequency response or the Elex’s speed, but at the 1:40 mark of the Trample by Turtles track, all the instruments are playing at the same time. At this point I’m having to concentrate much more to find the banjo playing in the background on the 660s2 compared to the Elex. It could be the dip that’s causing this but regardless it’s easier to follow on the Elex. With that said, I don’t want to take away how much of a joy it is when listening to trance, drum and bass, and fast electronic music.



Microdetail: I found I kept flip-flopping on whether the 660s2 was more resolving than the 650. The higher extension, paired with the much better background, lent to instruments popping out of the background with what seemed to be more detail. When I would switch back to the 650 I still heard those smaller details just without background being as black. I still believe that the 660s2 is more resolving than the 650s but slightly. The 660s2 does come away swinging when it comes to bass texture. The s2 does an impressive job of giving you information you can’t hear on either then Elex or 650. I really must give this one to Sennheiser.

Bass: The 660s2 hands down murders the 650 when it comes to bass. The speed, the tightness, the detail dunks all over it. This is not Atrium levels of texture, but that headphone came to mind when I heard these. The mid-range has more propulsion, the s2 easily extends lower than either headphone, with a more defined rumble. They are not anywhere near planar subbass extension and rumble, but it does a good job of presenting itself. Another note, these have better rumble and low-end extension than the Verite Open.

Couple of notes: The 660s2 sound thin and lifeless on a low impedance amp. They need a higher z-out to give it some meat on the bones, give it that bass propulsion, and allow its dynamism to show off. Hence why I paired them with the TU-8600s and to bring them in line with what I heard on the Elex. The tone of these headphones is more natural compared to the Elex. On the other hand, you are losing some of that mid-range magic from the 650s moving to the 660s2s. It’s there but switching to the 650s after felt like putting on your favorite t-shirt and sweats after a long day at work. @yotacowboy did mention that he found these fatiguing after listening to them. I also found the same thing which could be attributed to the dynamics, bass, and the extended treble. Something about it had me turning the volume down when I could turn up the 650s without issue.



Conclusion: So what do I think? I think this is a great addition to the Sennheiser line. Some of the issues found in the 650s are addressed in the 660s2. It’s a faster, quick, punchier, clearer, and extended headphone. Do I feel that it’s worth the $600 asking price? I’m just not sure it is. If we look at a value to cost, we have headphones like the Elex which go on sale occasionally around $500 or the Mass Drop Aeon Flow open at $449. If you’re willing to sacrifice some slight low-end extension, then you can grab yourself a very similar sounding headphone. If these were priced lower, say at around $400 – 450, I think they would be a great proposition. For those of you who own the JAR600 or 650s, keep trucking with those. This is not the droid you’re looking for.

 

How does the S2 sound out of the SW51+ ?

 

It’s ok. I’d prefer the 650 out of the SW51 than the 660s2. They sound much better out of a higher z-out.

 

Oops... forgot to mention my chain. It's a bunch of things. In order of increasing output impedance:

Geek Out V2+
Schiit Magni Piety
iBasso DX300 with AMP13
Eddie Current Zana Deux

DAC is either built in to some of those sources or I used Bifrost 2.

I have both a warmer (Fivre brown base 6SN7) and a brighter (Philips Jan green letter) tubes with ZD. The Philips Jan tube is the better one here and the ZD combo does give 660S2 a bit more "life" than anything else listed. But overall, I just have access to much "faster sounding" headphones and ultimately find the 660S2 unable to stand up against the likes of 580, 800 or the modded HE-6SE by @rhythmdevils here. It's not a bad headphone but trying to play in the >$500 league doesn't really help its case. All this is doing is probably just elevating the overall value of the HD6** line and similarly, HD580, which is now basically a mythical beast.

 

More 600 comparisons, please!

We all know the 650 is trash and that the 600 is the true king.

 

Received my pair of 660S2 last week but haven’t had any time for detailed comparisons with HD650, so will reserve overall review for some time.

However I will also reiterate that it’s a bit fatiguing to listen to for long sessions. But a pad swap to some well worn pads from my HD650 and that fatigue is completely gone. So it’s possible even some mild pad wear may reduce this feeling for folks that are bothered by it. With the old pads I have now, which are really old, the sound is somewhat darker, so may not be up everyone’s alley, but makes them a very smooth listen compared to the new pads.

Curious if anyone else has done some pad swapping with older 6X0 pads and found differences/improvements?

 

If you scroll up, you'll see I noted the differences. It's a bit more than just pad wear. It looks like the new design of the pad is emphasizing a certain peak rather than just smoothing out the treble range like the old pads. Seems like that's an intentional design decision to try and salvage treble since the overall tonality is so dark. What's more interesting is that the old pads to me sound... both brighter and also less fatiguing.

Getting brand new HD6** pads in today to do one final round of comparison to be "perfectly fair" to 660S2 but I don't think things will change much.