Sennheiser HD 660S headphones review

Sennheiser launched the HD 660S2 open-back headphones this year – but are their 2017 predecessor still worthy of your money?

Sennheiser HD 660 S
(Image: © Sennheiser)

Louder Verdict

Though they’ve since been usurped by their successor, these 2017 headphones are still an excellent choice


  • +

    Lightweight and comfy

  • +

    Sound quality is excellent


  • -

    Bass could be better

  • -

    Not wireless

  • -

    They don’t fold

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To really get the most from your music, then a good pair of headphones is pretty much essential. After all, the last thing you want when playing your all-time favourite album is to suffer tinny audio, earache or a flagging battery halfway through your listen. In the audio business for more than 75 years, German company Sennheiser has a reputation for making classy headphones, from its Momentum 3 Wireless over-ears to its Momentum True Wireless 2 earphones. So, anything bearing that name is likely to give you a fairly satisfying listening experience. 

Here, I'm taking a closer look at one of the brand’s more premium offerings, the Sennheiser HD 660S. Launched in 2017 as the latest addition to the esteemed HD 600 series, these wired, open-back headphones were described by the manufacturer as offering “the perfect blend of power and control”. However, with a new version – the HD 660S2 – launched earlier this year, should you still consider buying these headphones in 2023? Let’s find out.

Sennheiser HD 660S review: Design

Whether a pair of headphones looks good or not boils down to personal taste, but I'm rather fond of these Sennheiser headphones. Like the HD 600 and HD 650 before them, they boast a smooth, hard-plastic finish (in black only) and an eye-catching, stainless-steel grille on the back of each ear cup. The latter provide ventilation for the headphones' updated drivers, enabling what Sennheiser describes as “consistent control of air displacement to reduce turbulence”.

As for what they’re like to wear, the HD 660S are very comfortable thanks to their light weight of 260g and generous amount of soft cushioning around the headband and earcups. They also offer just the right level of clamping – they’re not ridiculously tight, but they’re grippy enough to prevent them slipping off the moment you start bopping. While the ear cups swivel to some degree, allowing you to get them at just the right angle for your head shape, the headphones aren’t foldable, meaning they’ll take up extra room in your luggage if you're using them on the daily commute or holiday journey.

Finally, these wired headphones are packaged with two three-metre cables – one with a 6.3mm stereo connector and the other with a balanced 4.4mm connector – ensuring that you can play your music on a range of devices.  

Sennheiser HD 660S review: Features

Sennheiser HD 660S

(Image credit: Sennheiser)

For these headphones, Sennheiser revised the driver set-ups seen in previous HD 600 iterations, equipping the headphones with specially ventilated 42mm transducers that offer a lower overall impedance of 150 ohms. One of the reasons for this was to make the HD 660S more compatible with portable devices such as smartphones and digital audio players. 

However, for the HD 660S2, the company has reverted back to 38mm drivers – and also added an ultra-light aluminium voice coil – which has bumped the impedance back up to 300 ohms. In my opinion, this results in even better clarity and more resonant bass than what the Sennheiser HD 660S offer, but it does mean you’ll require a headphone amp to get the best out of them.

A couple of additional stats for you: the HD 660S offer a frequency response of between 9Hz and 41.5kHz, while their sound pressure level clocks in at 104dB.

Sennheiser HD 660S review: Sound

If you’ve splashed out on an expensive pair of headphones, you would expect them to sound fantastic – and the Sennheiser HD 660S are certainly impressive. With a spacious soundstage, facilitated by reduced harmonic distortion, each instrument or voice is allowed to express itself. Timing is on-point, too, with the headphones keeping up with even the most complex of tempo changes like a world-class conductor. 

As for the different frequencies, the mid-ranges are pretty spectacular, with acoustic strumming and synth chords sounding as fresh and lively as a spring daisy. The highs, while ever so slightly warmer than I'd like, also sound clear and captivating. My one gripe is with the bottom end, which never quite delivers the impact I'm looking for, especially when listening to a bit of vintage rock or metal. This is something that’s been addressed with the latest version of these headphones – though you’ll have to pay a fair bit more for those since these original headphones are currently being sold by the manufacturer at a sizeable discount. 

Sennheiser HD 660S review: The alternatives

If you’ve got the money, then it’s worth considering the latest edition of these headphones, the Sennheiser HD 660S2, as they sound even better than the originals with improved clarity and more resonant bass. Just bear in mind they have a much higher impedance, meaning you’ll need a headphone amp to get the maximum listening pleasure from them.

If you prefer wireless headphones, you’ll struggle to find better than the Sony WH-1000XM5. Offering fabulous sound quality, best-in-class noise cancelling and a 30-hour battery life, these Japanese-made headphones are a splendid all-around package.

Paul Dimery

Paul has spent the past eight years testing and writing about gadgets and technology for the likes of Louder, T3 and TechRadar. He might not have the wealth or the looks of Tony Stark, but when it comes to knowing about the latest cool kit, Paul would surely give Iron-Man a run for his money. As for his musical leanings, Paul likes everything from Weyes Blood to Nirvana. If it's got a good melody, he's on board with it.