Review: Sennheiser HD660 S – Blended

Sennheiser HD660 S

Build Quality & Comfort

 

Like its brothers, the new Sennheiser HD660 S is also made in Ireland. Looking at the limited differences in design, that’s only a normal decision as well. Quality wise, Sennheiser did make one very important improvement however. As you probably know the “old” HD600 and H650 headbands suffer from paint chipping away when they’re heavily used (see pic). With the new color scheme and paint job, this no longer is or will be the case. In fact it’s not new as Sennheiser already addressed this in their Massdrop HD6XX headphone.

Sennheiser HD660 S

Sennheiser HD660 S

According to Sennheiser the robust yet lightweight construction makes listening supremely comfortable. The elliptical ear cups are shaped to follow the anatomy of the ear, while thick padding on the headband and the replaceable ear cushions provides a relaxing and luxurious experience that places the enjoyment of music at center stage. We already know this from the HD600 and HD650 of course and with only 290g, the HD660 S simply is one of the best fitting and most comfortable headphones on the market. You can wear it for hours and it won’t bug you for a minute, I love it. If you have a really big head however, you might find the clamping force of the HD660 S to be a bit much. But just like with the other Senns that can easily be addressed by stretching out the headband by putting a couple of books between them. It’s nothing to worry about.

Everything about the HD 660 S makes listening a pure pleasure – not least its strong yet lightweight open construction. The elliptical ear cups are shaped to follow the anatomy of the ear, while thick padding on the headband and the replaceable ear cushions guarantee hours and hours of listening in supreme comfort.

Cables

The former HD6XX models always came with a single long copper based cable, finished with a 6.3mm plug. The 300Ohm headphones need an amp to sound best so this was only a normal choice. Back in the days the audiophiles weren’t as occupied with balanced connections as they are now, so there was no real need for balanced headphone cables cables either.

Sennheiser HD660 S

Sennheiser HD660 S

On top of that Sennheiser only recently officially confirmed to adopt the Sony 4.4mm Pentaconn balanced connector and this connector now also is incorporated in their new HDV 820 DAC/amplifier unit. That in combination with the fact that the new HD660 S with its 150Ohm impedance is a lot easier to drive, made Sennheiser supply a 4.4mm finished cable as well. We’ll get into detail about this later but the Sony NW-WM1Z and HD660 S combo in balanced mode really is something special sound-wise.

Because of the HD660 S being easier to drive (Senn is even promoting the HD660 S in combination with DAPs), Sennheiser also includes the typical 3.5mm Grado adaptor in the box. So in the end you have 3 full-fledged cables to use with your new HD660 S. Well done Sennheiser!

Sound

Actually, it turns out I never officially reviewed the HD600 and HD6650 myself, Dave did that for us. That might come as a surprise as I’m always saying good things about them and because I use them in almost every single review. To me the HD650 still is “The King” and of the 6-series I now own the HD600, HD650, HD6XX and HD660 S.

“The headphones deliver an exceptionally accurate and transparent sound that also has an expressiveness that immerses you in every emotion and nuance of music.”

Before going in to the HD660 S even more, let’s quickly recap what the HD600 and HD650 sound like. The HD600 is the fastest of the three, and it is a headphone that is loved by many rock fans for its pace. The HD600 has great clarity and has a more neutral tuning, but always with a musical approach. I actually started my Sennheiser journey with the HD600 and I loved it. That was until I also bought the HD650 and it quickly won me over with is slower, warmer and smoother tuning. Some say the HD650 sound veiled and dark and while I see what they mean, I would put it that way. And fact is that your source is very important in this story, as it will alter the end result.

Sennheiser HD660 S

Sennheiser HD660 S

Made for the demanding listener, the HD 660 S surpasses the exceptional performance of its predecessor, the legendary HD 650. With a crisp bass, excellent mid-frequency response, and a gentle, pleasantly natural treble, the HD 660 S has an expressiveness that immerses you in every emotion and nuance of music. Still, it always stays exceptionally accurate and transparent

So basically there are three groups of people: those who like both headphones, those who prefer the HD600 and those wo like the HD650 most. Going on how the HD660 S sounds, it to me is clear that Sennheiser designed this headphone to (try to) please both groups of people. The HD660 S has the speed, transparency and clarity of the HD600, combined with the bass, naturalness and musicality of the HD650. It’s like the perfect headphone if you can’t decide which of the “old ones” you like most. Those not liking the “veiled’ nature of the HD650 will love the more clear HD660 S and those who find the HD600 too sterile, will love the more natural HD660 S. How can it not be a great headphone?

More Sound + HD600 & HD650

The Sennheiser HD660 S of course is a fully open headphone and you get a really nice wide and deep sound stage with a very natural sense of air and spaciousness. The overall pace of the HD660 S is more like that of the HD600 but it is not exactly the same to my ears either. It definitely is quicker than the HD650, there’s no doubt about that. The mids are very much like those in the HD650 on the other hand, and you get a natural, somewhat smoother delivery with a very high musicality factor and exceptionally good voices. The HD650’s bass isn’t as tight as the HD600’s or HD660’s bass and the HF660 S’ bass is tighter and faster than that of the HD650. If you Google for the FR curves you’ll be surprised to see these 3 headphones, up to the treble part, actually are very close together. This however doesn’t translate identically when you’re listening to them. The bass, mids and treble in all 3 headphones are different. And it might even be the treble section in which they’re most different, the HD660 S is very particular in that area.

Sennheiser HD660 S

Sennheiser HD660 S

The blackness of the background still is typical of Sennheiser but what I really want to talk some more about it how using the balanced cable changes the sound signature. Actually it’s not only by changing to balanced that the sound changes, the source used also impacts the HD660 S’ performance quite a lot, but more on that in a bit. When taking the Sony NW-WM1Z as source it is quite easy to switch between the single ended and balanced output. With the SE output you get a more neutral and fast presentation, with (again) a neutral amount of bass and treble which is more to the forward and slightly brighter side. Switch to the 4.4 balanced cable and you’ll get bass with bigger impact, more musical and slightly thicker mids and softer, yet still energetic treble. Especially the bass presence using the balanced output is impressive, but it really affects the mids, voices and treble as well. It makes the HD660 S sound more like the HD650 where the single ended cable makes it tilt more to the HD600 side.

Even more on SOUND on Page THREE of this review, after the click!

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Lieven is living in Europe and he's the leader of the gang. He's running Headfonia as a side project next to his full time day job in Digital Marketing & Consultancy. He's a big fan of tube amps and custom inear monitors and has published hundreds of product reviews over the years.

23 Comments

  • Reply April 3, 2018

    Musikverein

    A sane and in a word balanced review. Kudos, Lieven.
    The best thing of the 660s to my mind is, besides of the psychoacoustic blended-ness, are its convenience factors so to say.
    First, it has all necessary cabling coming with it and you will just need an additional adapter f.i. 2,5 to 4,4mm balanced and then that is it. You arrived a high ends heavens gate.
    Second, it can be driven with stuff starting with a Dragonfly Red, iFi nano, Mojo etc. to certain satisfaction of even audiophile gourmets. This indeed is new in HD6.. land when until now you needed serious solid state or tube based gear, to be honest 🙂

    • Reply April 3, 2018

      dale thorn

      Great observations, you can’t lose with the 660s.

    • Reply April 4, 2018

      Lieven

      Thank you. That is definitely the case and I applaud the multi-cable thing 🙂

    • Reply May 30, 2018

      Veri

      Indeed. 6-series sound without breaking the bank (too much).

  • Reply April 4, 2018

    Michel I

    Nice review again, Lieven, thank you.

    However, I don’t share your conclusion. The differences are small with the older HD600 and HD650, and there is a significant difference in street price: at this moment in Europe 429 Euro for the 660s but only 262 Euro for the 600, 315 Euro for the 650, and 435 Euro for the 700 (amazon.de).
    The balanced cable is exotic; most of us will need an adaptor or another cable to use it with our balanced headamps.
    The 600 is the best choice at this moment !

    • Reply April 5, 2018

      oliwek

      … then I still wonder : is the 600 the best choice when paired with portable sources, such as Mojo (single ended) and above all balanced with something like Hiby R6 (with a 2.5mm TRRS to 4.4 adapter) ?
      (if some people can comment on the results they get with HD600 or 650 with Mojo, you are welcome, as the reply from Musikverein lets me believe it’s maybe not ideal).

      • Reply April 5, 2018

        Michel I

        I think you need a good, powerfull amp for all the members of the 300 Ohm family, including the Massdrop x Sennheiser HD 6XX that you can buy this month on massdrop.com at 200 $ ( + 15 $ delivery outside the US), but also for the 150 Ohm 660s. The power of a Mojo is simply not enough.

  • Reply April 5, 2018

    Hans

    Hi Lieven, great review!

    The review grabbed my attention when you mentioned: “With the Sony DAP, even in single ended mode, you get a warmer, slower sound which also is very musical. You get bigger bass, thicker mids and soft yet detailed treble”

    Although this is the NW-WM1Z, the bigger bass, thicker mids and soft detailed treble was exactly what I thought when I heard the NW-A45 compared to LG V20.

    Maybe one day Headfonia can review the NW-A45 and see if the implementation of the same digital amp stays faithful to the Sony sound signature for much cheaper 🙂

  • Reply April 5, 2018

    MhtLion

    Thanks for another great review!! I have V281 and Senn HD6XX, which I love the paring but just sometimes I wish for more treble energy. I was torn between HD600 vs HD660S while I’m waiting for HD820 to be released. I have a sense that out of the balanced of V281, HD600 maybe the best out of three for my taste.

  • Reply April 6, 2018

    Marc

    Recently treated myself to HD 660S to replace my aging HD 580 and paired it with the Massdrop Cavalli CTH + SDAC combo. Sounds great!

  • Reply April 18, 2018

    Dom Sweat

    Although I have yet to try a pair of open-back Sennheiser ‘phones I’ve heard nothing but good things about them.

    The Sennheiser HD 660s seem like a pretty good option for consuming the more spacious sound that these are well known for.

    Would these be a good entry level pair of open back headphones or would you suggest trying a less expensive pair at first?

    • Reply April 18, 2018

      dale thorn

      I wouldn’t go less expensive than entry level. The 660s is a great headphone, and how much you’ll like it will depend on many variables – your music, your source, your amp, etc.

  • Reply May 19, 2018

    Lukas

    its good headphones for games? which is better with better sound stage? Hd 660 s or Hd 700 ?

  • Reply June 22, 2018

    DC

    Lieven, for those looking for the smooth and slow sound with pronounced bass, but worth going for the 650 or would it be better to go for the new 660s and try a smooth signature amplifier to make the headphones more romantic?
    You say that with the right setting the 660s gets softer and with more pronounced bass, looking like the 650, so this 660s soft signature is nicer than the smooth natural of the 650?
    better go for the 650 that is smooth by nature or try to leave the 660s romantic using an amplifier that leaves its signature?

    • Reply June 24, 2018

      Lieven

      In that case I would still go for the HD650, as it does that best

      • Reply June 26, 2018

        DC

        Thank you Lieven! If the 650 is the only one with this smooth signature of the HD6xx line up to the 800s, sennheiser should not discontinue the 650. I almost sold my 650 recently to buy the 660s hoping for a smooth signature but easier to amplify. But the King is still king, I will continue with the 650, because it was the right choice of signature that I made, with the help of serious reviews like yours.
        The sennheiser 650 has been improving over the last 14 years, including the easiest to drive drivers and more compatible with multiple amplifiers, they also said the newer paint is more resilient.

  • Reply September 20, 2018

    Matt

    Hi Leiven, thanks for this review. I’m considering getting some over ear headphones for when I travel overseas to replace my Shure SE425s. I listened mostly to classical music. Would the HD660 be a reasonable match with a Fit X5 2nd Gen DAP?
    Thanks for your help

  • Reply September 28, 2018

    Juan

    Awesome review… Love Headfonia reviews. Any chance we will get a HD820 Review anytime soon?

  • Reply September 28, 2018

    Lieven

    Not sure when but yessssss

  • Reply October 9, 2018

    Oost

    Thank you! Very informative. Any comparison to the LCD-2(C/F)? Both with Mojo as amp.
    Which is best for classical music?Piano, vocals, symphonies?

  • Reply November 29, 2018

    Moosa

    Thanks a bunch for this detailed review
    Do you think the KANN can be paired with this headphone?
    Thanks

    • Reply November 30, 2018

      Lieven

      Oh yes, though a bigger amp is always better

      • Reply December 1, 2018

        Moosa

        Thank you so much
        So this means I will definitely get it:)
        Thanks again

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