Sennheiser HD 660S2 review

Will Sennheiser’s latest audiophile headphones become a cult classic? Tested at £499 / $599 / AU$849

Over-ear headphones: Sennheiser HD 660S2
(Image: © What Hi-Fi?)

What Hi-Fi? Verdict

The Sennheisers have a charming smoothness to their sound, but their soft bass and lack of dynamic thrust hold them back.


  • +

    Breathtaking midrange

  • +

    Relaxed, undemanding listen

  • +

    Smooth presentation


  • -

    Soft bass

  • -

    Can be bettered for dynamics and detail

Why you can trust What Hi-Fi? Our expert team reviews products in dedicated test rooms, to help you make the best choice for your budget. Find out more about how we test.

There aren’t many headphones with as much heritage and history as the Sennheiser HD 600. The fact that you can still waltz onto the Sennheiser website and buy a pair, despite the model being well over twenty years old, just goes to show they’re still a respected icon and part of the headphone market furniture.

Over the years, a number of new versions have launched, including the HD 650 and HD 660, not to mention the very latest version we are testing here; the Sennheiser HD 660S2.


Over-ear headphones: Sennheiser HD 660S2

(Image credit: Sennheiser)

The Sennheiser HD 660S2 cost £499 ($599 / AU$849) so this puts them in the premium wired headphones category. Their most natural rival would be the Beyerdynamic Amiron (£545), although at this level prices are quite spread out and you can buy excellent options if you spend a little more, and even a little less. It really depends on your budget.

Design & build

Over-ear headphones: Sennheiser HD 660S2

(Image credit: What Hi-Fi?)

Anyone familiar with this series of audiophile headphones will know the formula here. The Sennheiser HD 660S2 are an open-backed over-ear design, with this model sporting a 38mm driver complete with an ultra-light aluminium voice coil.

Peer through the perforated grille which covers the outer part of the headphones and you can see part of the inner workings behind the driver. The HD 660S2 use a vented magnet system to minimise distortion – Sennheiser has paid a lot of attention to the system used on these particular headphones to optimise the way air flows around the drive unit.

On the earpieces themselves you’ll find plush, generously-sized velour earpads which go easy on your ears – it’s like slipping your feet into a pair of posh (and very comfortable) slippers. During testing, the Sennheisers don’t struggle to envelop our ears and create a solid seal. Along the headband, the padding isn’t quite as generous, but it’s soft and springy, so you don’t feel any unwanted pressure on the top of your head.

Sennheiser HD 660S2 tech specs

Over-ear headphones: Sennheiser HD 660S2

(Image credit: Sennheiser)

Type Open-back, wired

Driver 38mm

Sensitivity 104dB

Impedance 300 ohms

Weight 260g

Cable length 1.8m (x2)

Cable type 6.3mm (with 3.5mm adaptor), 4.4mm balanced 

At just 260g, the HD 660S2 aren’t exactly heavy (Beyerdynamic’s Amiron headphones are 340g) and they don’t weigh us down during testing. Out of the box, it’s worth noting the clamping weight is a little on the firm side, but there isn’t too much pressure and over time we’d expect this to relax a little.

To get the earpieces positioned evenly you need to manipulate the left and right sliders – they’re a little stiff, but once you’ve got them in the right place you’re unlikely to find yourself playing around with the positioning.

In the box you get a 1.8m-long headphone cable with a 6.3mm connector, a 1.8m-long cable with a 4.4mm jack and a 6.3mm-to-3.5mm adapter.

As you’ve probably guessed from the design, the HD 660S2 aren’t for out-and-about listening – the furthest you’re likely to walk with these is from your amplifier to the chair in your listening room. Impedance is 300 ohms which indicates they’ll perform to their best when hooked up to something with a bit more grunt than a typical smartphone or laptop. We carry out most of our testing using a Chord Mojo 2 DAC – starting with amplification around this level will help to bring the best out of the HD 660S2.


Over-ear headphones: Sennheiser HD 660S2

(Image credit: What Hi-Fi?)

Anyone wanting an upfront sound from their headphones might want to shop elsewhere. The Sennheisers present music in a wonderfully relaxed manner and take every track in their stride. They are a ridiculously easy listen. Partner them with any genre of music and you can just sit back and let it flow through your ears.

The way the HD 606S2 handle the midrange and voices is a real highlight. Vocals sound super-smooth and ooze refinement. Play A-Ha’s MTV Unplugged version of Take On Me at 24-bit/94kHz and the Sennheisers paint a beautifully intimate picture. Morten Harket’s smooth tone is both captivating yet gentle with it. The accompanying instruments such as the guitar and piano are extra ingredients that add to this soothing rendition.

We up the pace with Bruce Springsteen’s Dancing In The Dark and the Sennheisers continue with their smooth, refined delivery. There isn’t a hard or harsh edge in sight and the headphones show rhythm, flow and swagger. There is a good sense of space around the different elements which allows you to dip in and out, focusing on one or just listening to the sum of all the various parts. They really are an easy, uncomplicated listen.

Play a more bass-heavy track, though, with more demanding dynamics, and the Sennheiser HD 660S2 start to struggle a tad. Billie Eilish’s Bad Guy demands tight, controlled, and dynamic bass. And, although the HD 66S2 can produce more than enough bass weight, it sounds soft by the standards set by rivals such as the Beyerdynamic Amiron. There’s a lack of tautness and punch which also stifles the low-reaching dynamics of the track. The best wired headphones at this level allow those bass kicks to make more of an impression.

And it’s the same story with Massive Attack’s Angel. The sense of spaciousness and refinement are to be applauded, but it’s the low frequencies that really make this track and although the Sennheisers display enough in terms of quantity, it’s the quality that’s lacking. The HD 660S2 don’t really communicate the build-up of drama in the track. The best pairs are capable of adding more detail and texture.


Over-ear headphones: Sennheiser HD 660S2

(Image credit: What Hi-Fi?)

The Sennheiser HD 660S2 are a really easy, uncomplicated listen. If you’re a fan of acoustic or vocal-heavy tracks, you’re going to love these over-ear headphones. Many will find the midrange worth the entrance fee alone. It’s just a shame they’re lacking when it comes to dynamics and punch in the bass department. If they could sharpen up their act in the lower frequencies you’d likely be looking at five-star performers.


  • Sound 4
  • Build 5
  • Comfort 5


Read our review of the Beyerdynamic Amiron

Also consider the Shure SRH1540

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