The Sennheiser HD 660 S are high-end open-back headphones. These are the kind you might use to listen to music at home, or to watch a movie late at night when you don’t want to disturb anyone else.
An open design is useless for the outdoors, but contributes to the Sennheiser HD 660 S’s wide, involving sound.
These headphones are a follow-up to the Sennheiser HD 650, considered a classic pair for well over a decade now. Sennheiser retains the warm, accessible tone for the HD 660 S, making this pair easy to recommend to virtually anyone who can afford the high price.
If you’re new to high-end headphones, the most important part of the Sennheiser HD 660 S to note is their basic style. These are open-back, and you can see the driver mountings through the grille on the back of each ear cup.
Practical knock-on effects are obvious. The Sennheiser HD 660 S don’t block out sound; they’ll freely leak anything you play through them. If you’re wearing them while working, you’ll find that the clack of the keyboard is as loud as the music playing.
The majority of true high-end headphones use this style, though, since it promotes a more ‘open’ sound. It also avoids overheating your ears. If I’m sitting down to watch a movie at home, I’ll always pick an open pair given the choice.
For a headphone of this type, the Sennheiser HD 660 S grip your head with reasonable force. It feels like they’re hugging your head, though, rather than clamping it thanks to the thick padding on the velour cups and neoprene-like pads on the headband. A surer fit also means theses headphones don’t fall of your head if you turn too quickly, which is useful if you’re buying for a home studio.
The Sennheiser HD 660 S look a lot like the HD 650, but Sennheiser has changed the design a little. Metallic grey plastic has been switched with black. They look a little more ordinary.
Build quality seems similar to the HD 650. Plastic doesn’t offer a luxurious feel, but the quality of the plastic used is excellent. These headphones are built to last. Cups and cables can be removed and replaced too.
Sennheiser includes a bunch of adapters to ensure most won’t need to buy after-market cables. The standard cable is 3 metres long, ending in a 6.35mm jack. There’s a 3.5mm adapter cable in the box, along with a “Pentaconn” adapter. This offers a balanced output in a small 4.4mm jack.
As long as you’re buying for the home rather than portable use, there’s very little to dislike about the Sennheiser HD 660 S design.
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Sennheiser HD 660 S — Sound quality
These days, portable headphones tend to be at the top of most buyers’ to-buy lists. However, the Sennheiser HD 660 S prove full-size open headphones such as this are generally a better choice if you simply want a pair to use at home.
They have an excellent soundstage. It’s wide, expansive and superb stereo imaging and spatial imaging lets your ears explore arrangements much better than almost any closed pair at this price.
A big sound is also what you want for movies, to get closer to the experience of being surrounded by speakers rather than one where the audio is “in your head”.
Tonally the Sennheiser HD 660 S feel much like what they are, a reworking of the HD 650. That pair was/is known as one of Sennheiser’s “dark” sounding headphones, meaning music tends to sound full and rich, but not particularly bright or sharp.
These headphones have that same lower-mid range richness, but also have a little more high-frequency treble energy to balance it out. Listening closely, this added zing can come across a little “modular”, making the signature a little less of a coherent whole than, say, that of the classic AKG Q701. However, as long as you’re here for enjoyment rather than pro-style sound monitoring, you can interpret the Sennheiser HD 660 S as a bit of a “greatest hits” of the Sennheiser HD series.
You get the pleasant thickness of the HD 650 with a hint of the detail retrieval of the more expensive HD 800. I also think that many will prefer them to the AKG Q701, which sound thinner and colder. The Sennheiser HD 660 S are better ear-charmers, even if they’re not technically superior to that pair.
Comparing them directly to the AKG Q701 and the classic HiFiMAN HE-5 planar magnetic headphones, the HD 660 S display less soundstage width than the AKGs and less smooth mids than the planar HiFiMAN pair. However, the Sennheisers have more obvious energy and a less diffuse soundstage. Purists after the most balanced, neutral sound for their cash should perhaps look elsewhere.
Unlike the Momentum series, which has punchy sub-bass as its calling card, the HD 660 S have tightly-controlled bass. The frequencies are there, but so is the reserve expected of a higher-end headphone. To make up for this, the headphones delivers a little more power from fairly up-front mids.
Why buy the Sennheiser HD 660 S?
The Sennheiser HD 660 S find themselves in an odd spot. While the HD 700 launched at £600 more than five years ago, they’re now available for only slightly more money than this pair. As little as £10 at the time of writing.
Their design and fit is a little more special than that of the fairly conventional-looking HD 660 S too. However, while I no longer have the HD 700 to hand for a direct A/B test, comparisons with other contemporaries suggest that pair is “different” rather than flat-out better.
The Sennheiser HD 660 S are comfortable, have a great soundstage and a non-fatiguing combination of clarity and rich tone.
However, if you’re after a more neutral sound, you should also consider the Shure SRH1840, HiFiMAN HE560 or an AKG studio headphone such as the K712 Pro.