Sennheiser HD660s

Sennheiser HD660s


HD660s is the newest addition to the Sennheiser HD600 line, while also being the most expensive of them all. Because of the legacy of the HD600 this is a headphone a lot of people were looking forward to hearing. 

In the box

  • HD660s Headphones
  • Display box
  • 6.35mm  OFC cable
  • 4.4mm OFC cable
  • Paperwork

Build quality and accessories

Build quality of the headphones themselves is very good, everything feels solid from the hinges to the plastic cups and the outside grills. Nothing is creaking, materials feel fairly premium even though it’s mainly plastic. The cables however are yet again in case of Sennheirser janky, too long  for desk use and feeling cheap. 

Fit and comfort

I’ll just repeat my words from the review of the HD58X. “Fit is quite good, there’s a lot of adjustment on the headband to make sure the headphones fit correctly. However comfort in my case isn’t great, the clamp pressure is too high and it feels like the headphones want to squeeze my brain out, because of that I could only use them for an hour or so at the time”. In case of the HD660s the clam was slightly lower but still way too strong for my taste.


The tonality of the HD660s is surprisingly close to that of the HD58X, it’s warm and lush, it leans a touch more neutral than the latter but it still conserves similar tonal characteristics to the whole HD600 line. It is, however the least veiled out of all the HD600 line.


Fast, clear and accurate with good depth and texture. Depending of the source used the speed was different and the feel of it was different. On the RME ADI-2 DAC, the bass was fast and accurate but felt quite light at times, whereas on SuSy Dynalo Mk2 it was sweeter and had more body to it. The distortion is fairly minimal even though “Hanns Zimmer – Mountains” crescendo still present small issues.


Classical HD600 line midrange, with good detail retrieval and very good timbre. The detail isn’t forced, it’s there if you want but it’s not pushed into your brain. It renders the whole presentation quite natural overall. Upper midrange has a bit of grain but it isn’t very prominent.


Good detail and clarity, but lacks a bit of sparkle. Even though it extends well it lacks a bit of air. The grain is there but again it isn’t very noticeable unless you look for it. 

Imaging and Soundstage

Soundstage… This is probably my biggest disappointment, it feels lacking, narrow and with just an average depth and height. It isn’t as closed off as the rest of the HD600 series but it still isn’t anywhere near what I would expect of an open back headphone. However because of good layering the imaging holds a very good level even on busiest mixes.

Chicken Thoughts

The HD660S leaves me quite conflicted, on the one hand, they are without question, my favourite of the 600 line, in terms of build and sound, on the other, they are only “my favourite” by a half step making its price point hard to justify, putting the headphones in batting range with better offerings from competing brands. Tonally, they resemble their 600 line brethren, coming across as less veiled, less warm, and leaner or tighter in the bass regions. This reduction in veiled contributes to them appearing to be a little more resolving. The largest improvement the HD660S offer over the 600, 650, and indeed the 58X is the wider soundstage, no longer are we condemned to violently squishing our hands against our face, graduating instead to the lofty heights of competent, its staging no longer stifling, yet, not particularly “wide”. Thus it appears the HD660S are a welcome addition to the 600 line. However, even in a void where competing headphones manufacturers do not exist, the HD660S still come off as far too expensive at the msrp of £429, considering the HD6XX, drop’s rendition of the HD650, can be had for $220 in the US and $280 in the EU. Outside of this inexplicable void the price point puts the HD660S well within the range of the dt1990 or the HE560, both far better offerings from Beyerdynamic and Hifiman respectively.


HD660s is a good headphone, in certain aspects even very good. The problem to me is the price, it gets too close to things which outperform it as Chicken mentioned, both DT1990 and HE560 are fundamentally better headphones. I can, however see the appeal of it to people who do love the HD600s line and can’t quite decide whether they prefer the HD600 or HD650 as it tries to combine “the best” of both words while being the least veiled of its siblings. To me they aren’t worth their asking price, they stage is too narrow, the grain is there and the speed isn’t quite there. 

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