These are the latest version of Sennheiser’s long-running HD 660 series of open-back reference headphones, the new HD 660S2. They’re a bit of a “holy grail set of headphones” and I should probably pass on them now, especially given their price – £499 in the UK and $600 in the US. That’s an incredible price for most mere mortals, but then again, their reputation precedes them.
Sennheiser has been producing the HD 600 series in some form since the mid-1990s, and its design has remained largely unchanged over the past 25 years or so. Of course, there’s a good reason for this – many professionals and enthusiasts alike love these cans. The new HD 660S2 offers the same signature open design and solid plastic construction that more than justifies its high-end price tag.
With that in mind, the soft, velvety padding around the earcups makes them comfortable to wear, and there’s also plenty of padding on the headband. However, the clamping force provided by the HD 660S2s was a bit tight for my taste, and the headband in particular seemed rather stiff. Their lightweight 260g frame means they aren’t too uncomfortable, and the clamping force decreases slightly over time.
Like other open-back headphones, these headphones emit as much noise as they take in, but this compromise provides a wider soundstage because there are fewer physical restrictions on how far sound can travel.This can conveniently improve the perceived audio quality, although it means these headphones are intended for home use only – they allow exist There is too much noise during commuting, which makes go out Office use is too noisy.
As a reference headphone, the HD660S2 delivers the flattest sound profile possible, allowing you to hear your music as it is meant to be heard. Some headphones offer more bass response, while others, like the Grado SR325xs I reviewed a few months ago, are shinier and emphasize the high frequencies more. This realistic presentation makes the HD 660S2 a studio favorite, but they may not be as dynamic or exciting as more aggressively tuned alternatives.
With this in mind, the HD 660S2 delivers a more robust low end than previous models, which is perfectly reflected in The Who’s Eminence Front. Additionally, Peter Gabriel’s i/o’s “Dark Side” demonstrates the power of bass, with some particularly strong bass drums in the song’s chorus, while the intro to Daryl Hall and John Oates’s Maneater is reassuring. Rush’s “YYZ” is one of my favorite songs when it comes to testing bass, and it’s especially enjoyable to listen to with Sennheiser’s latest headphones. The bass here isn’t distorted or muddy, and has plenty of reassuring oomph.
The HD 660S2’s performance precision is also demonstrated by an in-depth study of its midrange. It handles vocals extremely well, 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 ever used, although the Grado SR325x come very close. Gloria Estefan’s “On Your Feet” also proves this, with its sharp and crisp synth sounds, Estefan’s excellent vocals, and the horns in the song’s chorus The sound also proves this.
There’s some excellent clarity across the frequency range, too, with realistic presentation across a variety of genres, from reggae to hard rock, which all sound exceptionally 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 weight well without being overbearing. Donald Fagen’s IGY sounded particularly pristine, as did Steely Dan’s Peg, proving that pairing a premium recording with the HD 660S2s can bring out its best.
Perhaps unsurprisingly for an open-back headphone, the HD 660S2s have a really good soundstage. The bongos on Earth, Wind & Fire’s September are right where they should be, staying crisp and clear while almost feeling like they’re far away from you, like they’re in the next room. Additionally, 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 the HD 660S2 has plenty of power, as well.
The combination of all the above features also makes the HD 660S2s an amazing gaming headset. The extra space and stunning soundstage provided by these open backs allow them to deliver one of the most immersive experiences I’ve had during long hours playing Forza Horizon 5, and the more powerful The low end allowed me to play a few rounds of CS:GO which was an absolute joy, even if I was never the best at the game itself.
My only issue with the HD 660S2s is how well it runs. Of course, as headphones designed for home listening with a DAC and amplifier, it’s probably not surprising that you can’t plug them directly into your PC or phone and expect them to work. The impedance of these headphones is 300 ohms, which is an order of magnitude higher than the 38 ohm Grados headphones I mentioned earlier. This means you’ll need a DAC or amplifier to fully run them, and these can be expensive – for reference, the Chord Mojo 2 I’m using here costs as much as the HD 660S2, and then we’re pushing that into four figures. In terms of price.
Yes, they’re expensive, and in the current climate it doesn’t seem right to recommend a £500/$600 set of headphones for everyone to try. However, the high price means the HD 660S2 is really only suitable for the most expert users who can get the most out of them. They are truly 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 watch out for a tight fit and excessive clamping force, which takes some getting used to.
