These are the latest iteration of Sennheiser’s long-running HD 660 series of open reference headphones, the new HD 660S2. They’re a bit of a “holy grail” set of headphones, especially given their price, which I should probably ditch right now – £499 in the UK, $600 in the US. That’s an unbelievable price for most mortals, but then again, their reputation precedes them.
Sennheiser has been producing the HD 600 series in some form since the mid-1990s, and the design has remained largely unchanged for the past 25 years or so. Of course, there’s good reason for that – many professionals and enthusiasts love these jars. The new HD 660S2 offers the same signature open design and solid plastic construction that justify its high-end price tag.
With that in mind, the soft, velvety padding around the earcups makes them comfortable to wear, and there’s plenty of padding on the headband, too. However, the clamping force provided by the HD 660S2s is a little tight for me, especially as the headband seems rather stiff. Their lightweight 260g frame means they’re not too uncomfortable, and the clamping force decreases slightly over time.
Like other open-back headphones, these emit as much noise as they absorb, but this compromise provides a wider soundstage because there are fewer physical restrictions on how far the sound can travel.This conveniently improves perceived audio quality, although it means these headphones are for home use only – they make exist Too much noise during commuting, making go out There is too much noise in the office.
As a reference headphone, the HD660S2 offers the flattest sound profile possible, allowing you to hear your music as it is. Some headphones offer more bass response, while others, like the Grado SR325xs I reviewed a few months ago, are shinier and put more emphasis on high frequencies. This realistic presentation makes the HD 660S2 a studio favorite, but they may not be as vibrant or exciting as their more aggressively tuned alternatives.
With this in mind, the HD 660S2 offers a more robust low end compared to the previous model, which was perfectly captured in The Who’s Eminence Front. Also, Peter Gabriel’s i/o’s “The Dark Side” is a testament to the power of the bass, with some particularly punchy bass drum in the song’s chorus, and a reassuring intro from Daryl Hall and John Oates’ Maneater. Rush’s “YYZ” is one of my favorite songs when testing bass, and it’s especially enjoyable to listen to with Sennheiser’s latest headphones. The bass here isn’t distorted or muddy, and it packs plenty of reassuring oomph.
The expressive precision of the HD 660S2 is also evident through a thorough study of its midrange. Its handling of vocals is excellent, as evidenced by James Taylor’s “Caroline I See You”. The smoothness of his vocals and fingerstyle guitar is unmatched by any other headphone I’ve used, though the Grado SR325x come very close. Gloria Estefan’s “On Your Feet” is evidence of this, too, with its sharp, crisp synths, as well as Estefan’s excellent vocals and the trumpet blare on the song’s chorus.
There’s also some excellent clarity across the frequency range, with a lifelike presence in a variety of genres, from reggae to hard rock, sounding particularly crisp. Bob Marley’s Could You Be Loved is an example of this, with the sharpness of the high-end cymbals and the HD 660S2 handling Marley’s vocals and low-end heft well without being aggressive. Donald Fagen’s IGY sounded particularly raw, as did Steely Dan’s Peg, proving that pairing a quality recording with the HD 660S2s brings out its best.
Perhaps unsurprisingly, for an open-back headphone, the soundstage of the HD 660S2s is indeed excellent. Earth, Wind & Fire’s mid-September tambourines are right where they should be, remaining crisp and clear, while almost feeling like they’re far away from you, as if in the next room. Also, the opening minute or so of Dire Strait’s Money For Nothing gives the competing synth and drum elements plenty of room to breathe and develop, and then the power of Mark Knopfler’s guitar drive suggests that the HD 660S2 also has plenty of power.
The combination of all the above features also makes the HD 660S2s an amazing gaming headset. The extra headroom and amazing soundstage these open backs afford allowed them to deliver one of the most immersive Forza Horizon 5 experiences I’ve had in a long run, while the beefier low end made playing a few rounds of CS:GO an absolute joy, even if I was never really good at the game itself.
My only problem with the HD 660S2s is how well it performs. Of course, as headphones designed for home listening with a DAC and amplifier, it’s probably not surprising that you can’t just plug them into your PC or phone and expect them to work. These headphones have an impedance of 300 ohms, which is an order of magnitude higher than the 38 ohm Grados headphones I mentioned earlier. That means you’ll need a DAC or amp to run them at all, and those can be expensive – for reference, the Chord Mojo 2 I’m using here costs about as much as the HD 660S2, and then we’re pushing prices into the four figures.
Yes, they’re expensive, and in the current climate, it doesn’t seem appropriate to recommend a £500/$600 set of headphones for everyone to try. However, the high price means that the HD 660S2 is really only suitable for the most professional users, as they can get the most out of them. They truly are one of the best headphones you can buy if you want realistic, warm and extremely precise sound, making them a real treat for gaming and music. You just have to be aware of the tight fit and excessive clamping force, which takes some getting used to.
