Sennheiser HD 660S2 Review

The HD series from Sennheiser has been a staple in the headphone world for quite some time. If the number six comes after the letters HD, then you can expect a great open-back headphone for an equally great price. Now, Sennheiser has updated one of its HD series headphones with the 660S2. This new version of the 660S aims to provide the same basic design but with a retuning of its signature sound. Does the HD 660S2 change enough to warrant the upgrade?

What You Get

• HD 660S2 Open-Back Headphones
• Headphone Cable – 4.4mm Balanced
• Headphone Cable – 6.35mm Unbalanced
• 6.35mm to 3.5mm Adapter
• Soft Carrying Case

Look & Feel

There isn’t much to note here if you’re familiar with the original HD 660S. Sennheiser has opted to go with the same basic structure as the 660S, which matches the design of the HD 600 series overall. The velour earpads and extra headband padding provide a snug but comfortable fit that seals excellently for supportive listening.

Design

While nothing quite changes on the outside, the inside of the 660S2 features some new components. The 660S2 adds a new ultra-light aluminum voice coil that is meant to minimize the weight of the driver. A new airflow system has also been implemented as well, hoping to minimize distortion and eliminate obstructive artifacts. These changes have had an effect on both the impedance and sensitivity of this driver. The 660S2 is now a 300 Ohm headphone, which means it requires a good amount of power from a dedicated headphone amplifier.

Soundstage

On the original 660S, the soundstage had a lot going for it, but it was never a standout to me. With the 660S2, Sennheiser improves the spatial abilities of these headphones, adding more depth and precision to the soundstage. While the 660S2 still doesn’t entirely extend the width of the 660S too significantly, it is able to weave itself through the stereo field much more articulately. The way sounds move from left to right on the 660S2 is noticeably more free-flowing. It doesn’t feel tied down to a strict flat plane and shows some added dimension to the sound. Your tracks will feel more naturally organized, even with its slightly deeper layering that makes all the difference.

Low End

Sennheiser has made it a major point with the 660S2 that the bass will be a strong focus in the headphone’s tuning. Hearing about this was strange to me since I had already felt the original 660S had a strong low-end presence already. What’s changed here is the more coordinated frequency content. The 660S2 stacks a whole range of bass tones in a more balanced pattern, giving the body of the response more form. Better depth is achieved with a clearer sub-bass texture that is allowed to separate itself properly. You’ll get a better vibration from bass instruments on the 660S2, and its grander display will never overcrowd the mix with a surface-level presentation.

Mids

Not much more is changed about the midrange on the 660S2. It appears that Sennheiser didn’t put as much focus into tuning up some of the frequency response here, but that isn’t much of a complaint for me. The low-mid warmth is still persistent on the 660S2, as is the flatness and neutrality of the fundamental mid-bands.

Highs

Unlike the mids, there is definitely a considerable change to the tuning of the highs on the 660S2. I felt that this version had significantly more bite to its treble. High-end coloration is a bigger factor in the sound signature of the 660S2. You’ll hear more sizzle and crispness from its timbre but don’t risk harshness. No piercing tones are perceived, but they don’t shy away from bright features either.

Summary

It’s weird that the S2 changes what it does but goes for an asking price that is a hundred dollars more than the original price. Whether or not you think it’s worth the price, the S2 does make its case with the improvements in the sound signature. The soundstage depth is my favorite improvement by far, but the bass and treble also undergo a significant enhancement. You could deduct some points for not going with a new design, but when you see the rest of the 600 series, it’s really not that egregious. Overall, I think the 600S2 is a good upgrade, but wouldn’t find it unreasonable if you decided that it’s not worth spending the extra money on.

The Sennheiser HD 660S2 is available February 21st, 2023 at Audio46.