Sennheiser HD 660S2

After spending a fair amount of time with the Sennheiser HD660S2, I was left somewhat disappointed, especially when comparing it to other similarly priced headphones like the HIFIMAN Ananda. While the HD660S2 continues Sennheiser's legacy of solid build quality and comfort, it simply doesn’t stand up to the competition in terms of sound performance.

The HD660S2's sound signature feels a bit dated. There’s a distinct lack of airiness, with the high frequencies sounding a little dull and closed off. For those who prefer a more laid-back sound, this might work, but I found the overall presentation to be somewhat lackluster.

In comparison, the HIFIMAN Ananda delivers a far more open and dynamic experience with clearer treble, more punchy bass, and a more expansive soundstage. The Ananda also has better detail retrieval, allowing for a more immersive listening experience. The HD660S2 feels like it’s lagging behind, especially for the price tag it commands.

To be fair, the HD660S2 excels in comfort, with a lightweight design and well-padded earcups, which could be a factor if you plan to wear them for long listening sessions. But when it comes to sound quality, it feels more like a headphone from a previous generation, rather than one that’s pushing boundaries in its price range.

Ultimately, while the HD660S2 might satisfy fans of Sennheiser’s classic house sound, it’s hard to justify the cost when there are options like the Ananda that offer a significantly more engaging and refined listening experience for a similar price.

I wanted something different then my sundara, so I thought I give the HD660S2 a try to see how it sounds to me.

Inside the box ,the HD660 S2 comes with two sets of cables, the Single End cables and then the 4.4mm Balanced cables, a 6.3mm to 3.5mm adapter which is a short cable, and finally a carry pouch.

Sadly there’s no 4.4mm to XLR adapter or an XLR balanced cable in the box, So if you wanting to run them balanced with a Dac/AMP or headphone amp lacks 4.4mm but has XLR, your going to have to either buy a 4.4mm to XLR adapter or a XLR balanced cable. Unfortunately I had to my self.



The first thing I did was see how light the headphones were, and they were super light, to the point I don’t feel them on the top of my head, unlike my sundara, I found the ear-pads to be very comfortable on my head, while wearing glasses. I do wish the ear-pads them self were a little bit more deeper, but it not really a problem. Durable wise they feel well made, But I wouldn’t want to drop them on any hard surfaces or too many times. The cables quality feels good too.





I had a little bit of trouble plugging in the cables into the cups, as it as a little tight, but evenly I got them in. Scared me a little bit as I thought I was going to break something.





Source used with the HD660 S2 was the EF499 with it set to Nos filter setting.





Hows it sound

Right off the bat, I don’t find them bright at all, to me they are smooth. With really good details, None of the instruments bump into each other, they can be heard separately. I feel like the sound stage is kinda large as it sounds like to be outside my head.



Its so easy to hear where every thing is located in a song. Including other singers voices, they also don’t overlap each other and isn’t thin, but have right amount of weight behind them. Singers feel like as if there very close to my, not right up in my face but close I would say.

I found the over all bass to be very good, it doesn’t bleed into the other frequencies, I would say its punchy, its the only way I can put it into words.



Games wise it works really well in games, in dead island 2, I had no issue with telling where zombies were, rather they was behind me, on my sides or in front of me. Gunshots and other weapons had enough behind them, it didn’t sound like my character was firing a cap gun. Sounded really good in the games I been playing.



Conclusion



I find my self enjoying the HD660 S2 a lot, I don’t regret buying these HD660 S2, I find my self enjoying it more then my Sundara.

Sennheiser has a unique problem: it is its own competition in many aspects.

Let me further clarify that statement.

The HD 650 were released over two decades ago. Even now they remain relevant, a staple even when it comes to open-back dynamic driver headphones.

So, how do you follow up a bonafide classic? There is no easy answer to that question. Sennheiser has been hard at work, trying to capture lightning in a bottle one more time.

The weight of expectations bears heavier on the HD 660S2 than any other pair of mid-range headphones. Perhaps unfairly so, but that’s what makes reviewing them worthwhile.

Read on.

Shout out to Sennheiser Germany, for providing the HD 660S2 on loan for review purposes.
This review originally appeared on Headphonesty.

Packaging​

Sennheiser has simplified the packaging of the 6xx series headphones to something rather generic.

While the old packaging of the HD 650 and HD 600 used to come with a heavy storage box and padded innards, the newer revisions arrive in recyclable cardboard cutouts.

In the box​

• Sennheiser HD 660S2 headphones
• 1.8m 6.35mm terminated cable
• 1.6m 4.4mm balanced cable
• 6.35mm to 3.5mm adapter cable

The good news is that the HD 600S2 come bundled with balanced and single-ended cables, making it easy to connect them to various sources without having to buy an aftermarket cable.

Design​

The HD 660S2 have a mostly plastic build with a spring steel headband.

Despite the usual sneer directed at plastic for not having a “premium” enough feel in hand, the HD 6xx series of headphones tend to last for a long time. My HD 650, for example, have been going strong for over seven years.

The HD 660S2 use a “dual-entry” cable system where both earcups use separate cable entries. This system is far more robust than the single-entry ones and does not rely on wires running through the headband.



The yokes have adequate sidewise movement, and the earcups rotate front-to-back by about 15 degrees, so I think most people won’t have issues getting a good seal. The left earcup can be identified by touch thanks to three raised dots near the headband.

Once again, Sennheiser takes care of the little details.

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The earpads are the same ones that come with the other HD 6xx series of headphones, which means that the sound signature will become more mid-centric as the pads wear over time. Fret not, though, as replacement pads are widely available.

Comfort​

The clamp force is slightly higher than I prefer. However, the pressure is so well distributed that no hotspots are formed.

Internals​

The Sennheiser HD 660S2 use 38mm drivers with a new magnet design despite utilizing a previous-generation housing.

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Sennheiser uses the same “vented” magnetic system on the HD 660S2 as the predecessor HD 660S. On the older models (e.g., HD 650 and HD 660), the air displacement at the back of the driver was controlled via foam inserts.

This new design utilizes stainless steel mesh, resulting in much tighter tolerance and superior material longevity.



The driver is also similar to the 660S except for the voice coil, which is now thinner (and thus, the increase in impedance, I assume). The housing is essentially the same as the HD 660S as well.

Sennheiser HD 660S2 Sound​

The HD 660S2 are mostly neutral with slight emphasis near the presence region.

The sub-bass reach and extension are a noticeable improvement over the preceding models.

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Bass​

Sub-bass used to be the Achilles’ heel for the HD 600 and HD 650, and while the HD 660S2 improved noticeably, the latest version of the HD 660S2 delivers the best performance.

The HD 660S2 produce excellent bass for a pair of open-back, dynamic-driver headphones.

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Bass is tight and controlled while having excellent speed and mid-bass texture. Deep, low rumble until 30Hz with superior definition. However, those used to accentuated sub-bass will not find it here.

Given that the HD 660S2 are meant to be neutral, reference-tuned headphones, the sub-bass not having a +10dB shelf makes absolute sense. The slam factor is an area that can be improved, as bass notes do not have a lot of physicality to them.

Midrange​

The mids are the bread and butter of the HD 6xx series of headphones. The HD 660S2 are no exception.

Sennheiser goes a slightly different route this time, with the upper-mids being less pronounced than the predecessors.

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This results in a more laid-back presentation of female vocals compared to the hyper-forward HD 600, while male vocals are not as lush-sounding as the HD 650.

If you are sensitive to shout, the HD 660S2 will be perfect for you.

Treble​

The aforementioned lower-treble peak around 6kHz can be tiring for treble-sensitive people. I experience fatigue when listening to poorly mastered tracks. Certain rock and metal songs, e.g., Red Hot Chilli Pepper’s Californication, are susceptible here.

This peak aids in finding mastering issues, however, especially for de-essing. So it’s there for a reason.

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Fortunately, the upper-treble is well-extended and has excellent tuning. Cymbals, hi-hats, and triangles resonate naturally, with precise attack and decay. Treble timbre is great as well, with no metallic “zing’ or “sheen” affecting the high notes.

Overall detail and resolution are very good, but the HD 660S2 fall behind some mid-range planar magnetic headphones.

Soundstage and imaging​

Soundstage is average for an open-back, but these don’t sound as closed-in as the HD 600 or HD 650. Stage depth is also improved, with frontal projection better reproduced.

Imaging is precise with accurate instrument placement.

Dynamics and speed​

Macrodynamic punch is fairly good, even though these aren’t the last word for overall slam and punch.

Microdynamics (gradual shifts in volume) are excellent, on the other hand. Separation is also above average, but some mid-range planars (e.g., the Hifiman Ananda Nano) are better.

Comparisons​

Vs Sennheiser HD 650​

Sennheiser’s HD 650 are legendary in their own right and are massively popular even 20 years after launch. The HD 660S2 manage to noticeably improve the bass response over the older model.

There really is no contest – the HD 660S2 bass is in another league compared to the HD 650.

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The HD 650 have noticeable distortion in the sub-bass region, and in busy tracks, bass notes tend to smear into each other. After some modding, I have slightly improved the distortion characteristics of my own HD 650, but even then, you reach the limits fairly quickly.



Another aspect that has seen a jump is the stage width. While the HD 660S2 are not particularly wide-sounding, they fare much better than the HD 650. A reason for this is the less forward upper-midrange, while the bass extension also helps create a sense of depth.

The upper-treble is a matter of taste. I find them both well-tuned in this regard, with the HD 660S2 perhaps being a tad more resolving. However, the lower-treble is where I much prefer the HD 650.

For male vocals, the lushness of the HD 650 remain unmatched for me. For vocal-centric tracks, I gravitate towards the HD 650 for this reason, while for instrumentals and more energetic tracks, the HD 660S2 became the natural pick.

Overall, the HD 660S2 are better suited for most modern genres. At the same time, I cannot overlook the price tag, which is nearly twice that of the HD 6XX Drop variant of the HD 650. The performance upgrade hardly justifies such a massive price gap, so the HD 650/6XX still remain as good an option as ever.

Conclusion​

Sennheiser has made a practically perfect pair of studio monitors with the HD 660S2. This is what the HD 560S tried to be, and the HD 660S were touted as being, but neither could overcome the final hurdles.

Unfortunately, the price is higher than I consider “apt.” The MSRP is exaggerated for a product that is a slight upgrade over the last model – primarily offering improvement in the bass for existing HD 600 and HD 650 owners.

This puts me in a somewhat awkward position.

I really like the HD 660S2 and could live with them as my only pair of headphones – for the most part. They do not require a lot of amping (though I’d recommend picking a source with >5 Vrms and >10 ohm output impedance for best results). They sound great with every genre.

However, the market has grown so competitive that the HD 660S2 do not offer everything they should at that price. For one, I expect better staging, and the bass slam could be improved. If you find the HD 660S2 on sale for a discount, they are well worth the purchase. At the MSRP, I have my reservations thanks to the old classics.