[DeweyCH]

I've really been enjoying the HD660S2 for the past 2 weeks, waited until now to get a short review together.


I have been comparing the HD660S2 to the HD600, HD660S (OG), and Focal Clear MG.



First thing I have to say, the bass is a great improvement over the original 660S, and I can safely say this is the best and cleanest bass I have heard in an HD6XX series headphone. To me, the bass just sounds straight up better than any of the other 6XX headphones. It sounds noticeably tighter and more defined than all of them, and I guess that's not surprising considering the improved sub bass was Sennheiser's marketing for this. I am also hearing better dynamics and just an overall more controlled sound over especially the 600 and 650. The 660S is very similar in this regard, but the lack of sub bass extension on the original 660S is noticeable in direct comparison. I definitely prefer the new S2. The S2 reminds me a little of the Focal headphones in terms of dynamics, although it's definitely a step or two down from that level, great but not top tier. I'd say it gets close though, the 660S2 is still a very snappy and fast sounding headphone, despite it having a warmer tonality. I've just been spoiled by the Focal Clear MG, which is more dynamic and punchy than any other headphone I've heard (including the Utopia 2022). The S2 has a better sense of punch and attack and speed than its siblings in the 600 lineup. The bass is cleaner on the Clear MG, unsurprisingly. I don't have the Elex anymore, but I think that would be a more interesting comparison because of the similar price ($599 vs $700). I can say for sure though, the midrange is more "liquid" and smooth on the S2 than any Focal I've heard, and the midrange also comes through clearer with more presence than the Focals.





Speaking of the midrange, that is one thing every Sennheiser 6XX headphone has always done better than most of the competition. The midrange is just gorgeous on the S2, the timbre is very natural and organic. Instruments and vocals especially are Sennheiser's strong point, and the 660S2 is no exception. While the S2 is somewhat warmer than both the 600 and original 660S, the detail sounds better to me. Aside from good detail, surprisingly I'm hearing more refinement and naturalness in the treble vs my Focal Clear MG and Hifiman HE-500 (not necessarily more detailed though). The treble also sounds like an upgrade over the other 600 series headphones, as good as they are. Another advantage the S2 has over the open back Focal headphones, the midrange and treble just sounds more cohesive and linear. The Clear MG has more sharpness and "glassy" timbre to the treble, which isn't all that natural much of the time, at least compared to the Sennheiser headphones. I'm aware I'm comparing a $600 headphone to an over $1,000 headphone, but it really goes to show you how well the 600 series have held up against the modern and more expensive stuff coming out. I would say the same about the older 650 and 600 which are around $300 now, but the S2 takes the resolution and technical performance up a notch. The performance of the S2 is very good, but don't expect it to beat the Clear MG in the areas of dynamic punch, soundstage width/depth, and bass resolution. However, I think the imaging might be taller on the 660S2, while the image is deeper on the Clear MG.




I prefer the midrange tuning of the S2, as well as the original 660S, over the 650 and 600. The 600 and 650 are excellent, but they always sounded a bit too forward for me. And although I did get used to it over the years, I generally prefer this more neutral tuning of the upper mids/lower treble. The only complaint I have about the tuning on the S2 and the original 660S (specifically this upper mids/lower treble) is there is slightly less presence at 3-4 kHz than I would like, some instruments lose presence and sound a bit dark sometimes. This however can be fixed easily with EQ, and even then I only add 2 dB in that frequency area. The S2 makes up for this slight recession by being richer and cleaner in the midrange than the older 600 models. The S2 also adds some space to the recording as opposed to the HD600 and HD650 presenting the music very close right directly in front of you, sometimes to a fault (granted this does work well with some recordings). Much of my impressions versus the HD600 line up exactly with what @SLC1966 said in their comparison on here. The 600 is very close and in your face while the 660S2 is better at surrounding and immersing you with more richness to the music. With the HD600 vocals being too forward for my tastes, and the Clear MG being a little too pushed far back for me, the HD660S2 is just perfect right in the middle of the two and now my favorite midrange/vocals presentation. Vocals and midrange centric instruments come through more naturally on the S2 compared to the upfront nature of the 600, and somehow the S2 sounds clearer and cleaner despite being warmer. But in particular, I think the S2 really shines with male and alto female voices. I recently modded a 6XX with the Custom Cans copper mass load and ZMF Suede pads, and as good as that sounds, I still think the 660S2 by itself with no mods sounds better. Also, the S2 really takes EQ very well, especially in the sub bass, much better than the 600 or 650 could ever do. You can hear it extend all the way down to 25 Hz using a sine sweep, even without an EQ boost. I would like to say something controversial many reviewers won't agree with, that the S2 is the HD600 + HD650 sub bass upgrade we have been waiting for, it outclasses the older models in that area.





All in all final thoughts, I'm really glad I picked these up. These are everything I wanted the original 660S to be. It still has the signature Sennheiser HD6XX series sound, but with even more welcome changes vs the regular 660S. It's basically the perfect Sennheiser headphone for my tastes. The sound presentation is warm and very natural, yet without the loss of intensity and engagement. The HD600 still has it's place in my collection, but for an all rounder that works well with all genres, I'd pick the S2. I'd go so far to say I like them better than the HD800S (from what I remember), not in terms of soundstage and imaging but as a whole package. Then again, I prefer a more neutral/warm tuning than the HD800 series. With a little EQ in the bass and upper midrange, the 660S2 is quickly becoming my new reference headphone.





Also, I'd like to share that this track below from the game Ori and the Blind Forest on the HD660S2 actually made me tear up. The female vocals come through so beautifully on the 660S2. Sennheiser is still king of vocals. And Mahler sounds pretty awesome too.

Ori is such a fabulous soundtrack. Video game soundtracks are a severely underrated/niche musical option - I have Ori on vinyl (along with quite a few more... my favorite is the ridiculous soundtrack for Katamari Damacy). Cheers to good taste!

 

[jonathan c]

I've really been enjoying the HD660S2 for the past 2 weeks, waited until now to get a short review together.


I have been comparing the HD660S2 to the HD600, HD660S (OG), and Focal Clear MG.



First thing I have to say, the bass is a great improvement over the original 660S, and I can safely say this is the best and cleanest bass I have heard in an HD6XX series headphone. To me, the bass just sounds straight up better than any of the other 6XX headphones. It sounds noticeably tighter and more defined than all of them, and I guess that's not surprising considering the improved sub bass was Sennheiser's marketing for this. I am also hearing better dynamics and just an overall more controlled sound over especially the 600 and 650. The 660S is very similar in this regard, but the lack of sub bass extension on the original 660S is noticeable in direct comparison. I definitely prefer the new S2. The S2 reminds me a little of the Focal headphones in terms of dynamics, although it's definitely a step or two down from that level, great but not top tier. I'd say it gets close though, the 660S2 is still a very snappy and fast sounding headphone, despite it having a warmer tonality. I've just been spoiled by the Focal Clear MG, which is more dynamic and punchy than any other headphone I've heard (including the Utopia 2022). The S2 has a better sense of punch and attack and speed than its siblings in the 600 lineup. The bass is cleaner on the Clear MG, unsurprisingly. I don't have the Elex anymore, but I think that would be a more interesting comparison because of the similar price ($599 vs $700). I can say for sure though, the midrange is more "liquid" and smooth on the S2 than any Focal I've heard, and the midrange also comes through clearer with more presence than the Focals.





Speaking of the midrange, that is one thing every Sennheiser 6XX headphone has always done better than most of the competition. The midrange is just gorgeous on the S2, the timbre is very natural and organic. Instruments and vocals especially are Sennheiser's strong point, and the 660S2 is no exception. While the S2 is somewhat warmer than both the 600 and original 660S, the detail sounds better to me. Aside from good detail, surprisingly I'm hearing more refinement and naturalness in the treble vs my Focal Clear MG and Hifiman HE-500 (not necessarily more detailed though). The treble also sounds like an upgrade over the other 600 series headphones, as good as they are. Another advantage the S2 has over the open back Focal headphones, the midrange and treble just sounds more cohesive and linear. The Clear MG has more sharpness and "glassy" timbre to the treble, which isn't all that natural much of the time, at least compared to the Sennheiser headphones. I'm aware I'm comparing a $600 headphone to an over $1,000 headphone, but it really goes to show you how well the 600 series have held up against the modern and more expensive stuff coming out. I would say the same about the older 650 and 600 which are around $300 now, but the S2 takes the resolution and technical performance up a notch. The performance of the S2 is very good, but don't expect it to beat the Clear MG in the areas of dynamic punch, soundstage width/depth, and bass resolution. However, I think the imaging might be taller on the 660S2, while the image is deeper on the Clear MG.




I prefer the midrange tuning of the S2, as well as the original 660S, over the 650 and 600. The 600 and 650 are excellent, but they always sounded a bit too forward for me. And although I did get used to it over the years, I generally prefer this more neutral tuning of the upper mids/lower treble. The only complaint I have about the tuning on the S2 and the original 660S (specifically this upper mids/lower treble) is there is slightly less presence at 3-4 kHz than I would like, some instruments lose presence and sound a bit dark sometimes. This however can be fixed easily with EQ, and even then I only add 2 dB in that frequency area. The S2 makes up for this slight recession by being richer and cleaner in the midrange than the older 600 models. The S2 also adds some space to the recording as opposed to the HD600 and HD650 presenting the music very close right directly in front of you, sometimes to a fault (granted this does work well with some recordings). Much of my impressions versus the HD600 line up exactly with what @SLC1966 said in their comparison on here. The 600 is very close and in your face while the 660S2 is better at surrounding and immersing you with more richness to the music. With the HD600 vocals being too forward for my tastes, and the Clear MG being a little too pushed far back for me, the HD660S2 is just perfect right in the middle of the two and now my favorite midrange/vocals presentation. Vocals and midrange centric instruments come through more naturally on the S2 compared to the upfront nature of the 600, and somehow the S2 sounds clearer and cleaner despite being warmer. But in particular, I think the S2 really shines with male and alto female voices. I recently modded a 6XX with the Custom Cans copper mass load and ZMF Suede pads, and as good as that sounds, I still think the 660S2 by itself with no mods sounds better. Also, the S2 really takes EQ very well, especially in the sub bass, much better than the 600 or 650 could ever do. You can hear it extend all the way down to 25 Hz using a sine sweep, even without an EQ boost. I would like to say something controversial many reviewers won't agree with, that the S2 is the HD600 + HD650 sub bass upgrade we have been waiting for, it outclasses the older models in that area.





All in all final thoughts, I'm really glad I picked these up. These are everything I wanted the original 660S to be. It still has the signature Sennheiser HD6XX series sound, but with even more welcome changes vs the regular 660S. It's basically the perfect Sennheiser headphone for my tastes. The sound presentation is warm and very natural, yet without the loss of intensity and engagement. The HD600 still has it's place in my collection, but for an all rounder that works well with all genres, I'd pick the S2. I'd go so far to say I like them better than the HD800S (from what I remember), not in terms of soundstage and imaging but as a whole package. Then again, I prefer a more neutral/warm tuning than the HD800 series. With a little EQ in the bass and upper midrange, the 660S2 is quickly becoming my new reference headphone.

Very well done . I think of 660S2 as a sonic descendant more of the 600 than of the 660. (Note: I use Custom Cans UK mod / ‘mesh’ mod on 600). 660S2 has become one of my “go to / swear by” headphones . The 660S2 does have the ‘mesh’ mod (foam replacement) also:

 

[pietcux]

So this is just the no foam mod?

 

[jonathan c]

So this is just the no foam mod?

There is a fine ‘mesh’ in lieu of the foam. Here is a closer view:

 

[jonathan c]

As the days get warmer, 660S2 dares to go output transformer-less and to catch some Rays:

[ Raytheon 6080WC, pair Raytheon CK-5670 in Woo Audio WA3 ]

 

[artvandelay9]

Very well done . I think of 660S2 as a sonic descendant more of the 600 than of the 660. (Note: I use Custom Cans UK mod / ‘mesh’ mod on 600). 660S2 has become one of my “go to / swear by” headphones . The 660S2 does have the ‘mesh’ mod (foam replacement) also:

I think this is a good quick summary. Unfortunately I sold my 600 a little over a year ago so I can't compare directly, but that's a thought I've had in my two months with the S2 alongside the 650. These two feel pretty different in a lot of ways, but my brain's memory of the 600 (which I owned for years) is recalling a less contrasty S2.

As the days get warmer, 660S2 dares to go output transformer-less and to catch some Rays: [ Raytheon 6080WC, pair Raytheon CK-5670 in Woo Audio WA3 ]

Wish I didn't see this. I loathe spending money on cables, but that matching weave is great.

 

[jonathan c]

I think this is a good quick summary. Unfortunately I sold my 600 a little over a year ago so I can't compare directly, but that's a thought I've had in my two months with the S2 alongside the 650. These two feel pretty different in a lot of ways, but my brain's memory of the 600 (which I owned for years) is recalling a less contrasty S2.



Wish I didn't see this. I loathe spending money on cables, but that matching weave is great.

Norne Audio Vygarde: black with copper seam.

 

[dogilainen]

I am deeply conflicted about this photo.

Care to elaborate? Is it the Squishmallow, the almost too short cable or what

And sorry if I ruined your day

 

[pietcux]

For me the HD660S2 completes the HD6XX line-up because it improves in all regards and I can enjoy to every kind of music, without fatigue, for endless hours. The only thing which I still need is a closed variant for some given scenarios.

 

[Rob80b]

For me the HD660S2 completes the HD6XX line-up because it improves in all regards and I can enjoy to every kind of music, without fatigue, for endless hours.

Ditto.

The only thing which I still need is a closed variant for some given scenarios.

Oddly, or maybe not, strange bed fellows, I'm finding the HD820 very similar in tone to the S2......

 

[pietcux]

Here is another ECM album which I can highly recommend. I listened to exactly these titles live in my hometown 2 years ago. Nik Bärtsch's Mobile "Continuum"
We had an "ECM" festival.

 

[funkymartyn]

For me the HD660S2 completes the HD6XX line-up because it improves in all regards and I can enjoy to every kind of music, without fatigue, for endless hours. The only thing which I still need is a closed variant for some given scenarios.

How about just picking up the Senn hd569 closed back. Mine new were £75. Worth keeping a eye out . Two leads, a 3.5mm tip, and a 6.35 mm tip. .

 

[pietcux]

How about just picking up the Senn hd569 closed back. Mine new were £75. Worth keeping a eye out . Two leads, a 3.5mm tip, and a 6.35 mm tip. .

Yes that is what clear minded people would do. But this is HeadFi......
Here is what I could use instead:

Same driver as the HD569 GSP600 closed back gaming headset. Good, but not HD660S2 worthy performance.

 

[jonathan c]

…. ? the headphone cousin of ? ….

 

[Luckyleo]

Could be, but the best humor always contains elements of truth...............