Sennheiser has long had a great reputation in the world of audiophile headphones - not necessarily for producing £5,000 headsets that will melt your ears, but rather for its incredible reliability.
The 600 series has had a few variants, and through them all has represented some of the best value in audio, bringing you incredibly crisp and detailed audio for a reasonable price. That price sees a jump for the new HD 660S2, so we've been checking out whether they're worth the upgrade.
Sennheiser HD 660S2
These are a pair of absolutely sumptuous audiophile headphones that are comfortable and sound superb, serving as the perfect gateway into hi-fi audio.However, they're a lot more expensive than other options Sennheiser offers and don't upgrade things hugely on the sound side. While they stand alone excellently, there might be better value to be found elsewhere.
- Sound is impeccable
- Really comfortable
- Comes with good cabling
- Fantastic detail
- High price
- Older 660S is cheaper and very nearly as good
- Velour ear-pads
- Available in black only
- Weighs 260g
Sennheiser hasn't exactly started off from scratch with the HD 660S2, and that's no surprise. It has a long lineage in the audiophile world, and its headphones have been evolving only slowly on this side of things.
In fact, if you look at the slightly older HD 660S and compare it to this new model, the only really obvious difference is the use of brass accents in a couple of places to make things stand out more.
There are, in fact, plenty of subtle design tweaks inside the earcups, but they're harder to see with the naked eye, and are designed around pretty complicated tweaks to the headphones' audio output.
Still, we think this is a pretty classy and neutral-looking pair of headphones, which matches its sound signature nicely. Of course, this is a completely open-back setup, so sound leakage is a constant and unavoidable side effect of a wide and expansive soundstage.
That means these are emphatically for home listening and solo sessions only - not to mention they're obviously heavily cabled to tether you to a high-quality audio source.
While a full DAC will obviously give you the highest level of fidelity and push the HD 660S2 to its limits, the reality is that as long as you're using a higher quality streaming service, you'll still get laudable results - even through a phone - but more on that later.
The cabling provided is long and straightforward, although the connectors to the earcups themselves are once again Sennheiser's own design, which slightly limits your ability to replace and repair them if they break.
The headphone's earcups are finished in a nice soft velour that remains comfortable even after a couple of hours, which is always welcome. The clamping isn't too forceful at all, in our experience, so this is a really comfortable pair of headphones to wear, and fairly lightweight at 260g.
That said, the price Sennheiser has attached, at a hair under $600 or £500, borders on the luxury, and this isn't really a luxury product, right down to the simple bag that accompanies it instead of a real storage case.
- 38mm dynamic transducers
- 8 - 41,500Hz frequency response
- 300 Ω impedence
Some audiophiles chase the holy grail of neutrality, the idea that you can hear music exactly as it was recorded, without any software or hardware distorting or changing sound signatures according to outside influences.
That's a laudable concept and it's one that Sennheiser often gets closer to than many alternatives, but it's actually not quite the core of the HD 660S2, which is actually arguably a little less neutral than its predecessor.
Sennheiser has subtly beefed up the low-end output here to give you a little more oomph if you're listening to music that warrants it.
This makes for richer delivery if you delve into bands that make the most of bass, whether it's crashing rock from Songs for the Deaf or the glitchy power of Justice's Waters of Nazareth.
Luckily, there's no compromise on detail in the bargain, so you're still going to get excellent performance from the HD 660S2 if you're sticking to classic music or lighter genres.
We used Tidal for most of our testing, and while audiophile converts won't need winning over, it's worth being clear that you will, even without a huge amount of experience, be able to easily tell the difference if you swap between high and low-bitrate audio options of tracks you love.
That game can keep you occupied for a while when you first unbox the headphones, frankly, but more seasoned listeners will simply sink into new and old material alike in confidence that they're hearing it very, very close to how it should sound.
Balance is a hard thing to come by in audio, but Sennheiser has managed it here, albeit in a way that doesn't make us feel like the leap from its other 600-series headphones is a generational one.
To spell that out further, if you already have a 600-series set that's still in solid condition, we don't think there's anything pressing about the HD 660S2 to make you upgrade, given its really chunky price tag.
In fact, with discounted prices available on a number of older models, picking exactly which option offers the best performance-per-pound will be a game that keeps enthusiasts occupied for quite some time, we'd wager.
If you're looking for a new set of home-listening open-back headphones and you don't really have a benchmark by which to measure them, there's no denying that the HD 660S2 represents a pretty excellent sonic option.
Sennheiser has upgraded its previous sound signatures in small, but fairly telling ways to deliver a superb package that can handle almost anything you throw its way.
However, the price tag it's attached to the HD 660S2 is a little hard to take right now, without some more luxurious touches to go with it. That's not helped by the fact some careful digging will provide bargains in the form of older Sennheiser 600-series headphones at potentially half the price. Which model you prefer might be a matter of how much work and research you're prepared to put into getting incredible home audio.