I Tried the Sennheiser HD 660S2 and I Think They Could Be My Endgame

The HD 660S2 are simply impeccable.
The HD 660S2 are simply impeccable.

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I could probably live with these as my only pair of headphones.

I took the challenge of reviewing the Sennheiser HD 660S2 headphones with skepticism on how they will surpass their predecessors.

But as soon as I tried them, the doubts turned to surprise, then to admiration. The HD 660S2 easily exceeded expectations with their unmatched balance of sound clarity and depth. Their build and comfort further elevated the experience, providing a listening experience that was as luxurious as it was long-lasting.

Read on as I unpack the features and experiences that position the HD 660S2 as a strong contender for my ultimate headphone choice.

Bass, Midrange, and Treble Performance

The Sennheiser HD 660S2 exhibit a mostly neutral sound signature with a slight emphasis near the presence region.

HD 660S2 offer better sub-bass reach and imaging over the aging HD 650.
HD 660S2 offer better sub-bass reach and imaging over the aging HD 650.

During my tests, I immediately noticed that the bass is a significant improvement over its predecessors. It’s tight, controlled, and extends deep into the low frequencies, reaching down to 30Hz.

This creates an excellent foundation without overpowering the overall sound profile.

Considering the HD 660S2’s aim to be neutral, reference-tuned headphones, the absence of a +10dB shelf in the sub-bass is understandable and aligns with their design philosophy.

However, those accustomed to a heavily accentuated sub-bass might find it lacking here. Yes, the bass notes are clear. But, it lacks a bit of “slam factor” or physicality, which detracts slightly from the overall impact.

In the midrange, the HD 660S2 shine with its bread-and-butter performance.

The mids are less pronounced than in previous models, offering a more laid-back presentation. This is very noticeable in how female vocals were rendered, offering a sense of clarity and space.

In the treble range, I observed a well-extended response with a peak around 6kHz. This peak can be potentially challenging for some. It could be slightly harsh with low-quality recordings. But, it was effective in unveiling details in well-mastered tracks.

Imaging, Macro, and Micro Dynamics

The Earmen ST-Amp drive the HD 660S2 well.
The Earmen ST-Amp drive the HD 660S2 well.

Diving deeper, I found that the HD 660S2’s staging is average, but their imaging stood out for its precision.

I was able to pinpoint the positions of different sound sources in complex tracks easily. This added an immersive quality to my listening experience, especially with well-mastered recordings.

I also found the punch in the macrodynamic to be fairly good. It didn’t reach the heights of overpowering slam. But, the headphones managed to convey a sense of energy and impact that felt balanced and appropriate for most genres.

However, it’s the microdynamics that genuinely stood out to me. The headphones adeptly handled subtle shifts in volume and offered excellent separation.

This was most apparent in acoustic and vocal-centric tracks. The delicate changes in the artists’ vocal inflections and the nuanced string vibrations on acoustic instruments were rendered with an impressive level of detail.

Build Quality

The familiar design of the 6XX series re-appears on the HD 660S2.
The familiar design of the 6XX series re-appears on the HD 660S2.

My experience with Sennheiser products, including the HD 650, which has lasted over seven years, reinforces my confidence in their build quality.

Sure, there’s a predominance of plastic in their construction. Yet, the headphones appear to be robust and well-assembled, suggesting durability and reliability.

My attention was particularly drawn to the dual-entry cable system. This feature not only enhances the structural integrity but also provides a practical ease of use. Since each earcup has a separate cable entry, you won’t have to worry about the headphones’ dependency on wires running through the headband.

The driver housing and damping scheme is similar to the older models, with the major improvement being the magnet system.
The driver housing and damping scheme is similar to the older models, with the major improvement being the magnet system.

Internally, the HD 660S2 employ 38mm drivers housed in a previous-generation design but with a new magnet system.

This blend of old and new is fascinating. While the housing remains familiar, the updated magnet design and vented magnetic system feature significant advancements.

Sennheiser has replaced the older foam inserts in the HD 660S2’s magnetic system with stainless steel mesh. This results in tighter tolerance and better material longevity.

The voice coil in the driver, however, is also thinner, which I suspect contributes to the increased impedance.

Comfort and Practicality

When I first put on the Sennheiser HD 660S2, I immediately noticed the clamping force, which was slightly more than I’m accustomed to. However, this didn’t lead to any discomfort, thanks to the even distribution of pressure, which avoided creating any pressure points on my head.

While the clamping force can be adjusted, it can void the warranty. So, I just chose not to alter them.
The foam padding has been improved, aiding in comfort. (From: Kazi)
The foam padding has been improved, aiding in comfort. (From: Kazi)

The open-back design did not offer any sound isolation, as expected. Yet, it contributes to a natural and spacious sound, which is a trade-off I’m willing to make for the quality of audio experience they provide.

In my experience, the absence of isolation wasn’t a significant issue. I predominantly use these headphones in quiet environments where external noise is minimal. This aspect might be a concern for some, but for me, it aligns with my usage scenarios.

The overall comfort is impressive, allowing for prolonged listening sessions without fatigue.

Of course, these headphones also have its fair share of flaws. For more information, check out my full review of the Sennheiser HD 660S2.

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