Sennheiser HiRes Audiophile Headphone (HD 660 S)

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In the extreme, it can have the tonal effect of sounding like a vocalist is speaking or singing through a toilet paper tube or cupping their hands over their mouth.

In this, and the following series of photos, the HD 600 is at left, the HD 650 at center, and the HD 660S is to the right. The extra extension on the Sennheiser HD 660S2’s mid and sub bass has probably been the unit’s most hyped detail ever since Sennheiser released its frequency response chart. but this was not the case at all for me on the HD 660S; I found its upper midrange to be very smooth. The midrange is where HD660S really shines, delivering loads of detail, excellent layering and separation, and a really strong natural presentation of instruments and vocals. The HD 650 and HD 600 have been around for almost two decades, but they continue to be a favorite amongst listeners.With the music at 100dB SPL, the leakage averages at 63dB SPL and peaks at 78dB SPL, which is way louder than the noise floor of an average office. My hearing quirks include a high sensitivity to midrange frequencies from just under 1KHz to around 3Khz, give or take.

On the one hand, this made the unboxing experience of the HD 660S2 a little less dramatic than that of the HD 660S.

On the upside, the plastic used feels decently solid and they also have detachable cables, which are easily replaceable, making them more durable.

The midrange is smoother and more natural on that stack with 660s than the 6XX and the treble is pleasant and reasonably detailed where the DT880 can get over-the-top sharp (especially on Atom). If you're not getting improvements on money spent on electronics you're missing out on half the fun.The Beyerdynamic DT 1990 PRO and the Sennheiser HD 660 S are both very good open-back audiophile headphones, each with their own different sound signature. While the HD 660 S was a bit brighter than the other two, it also lacked the nuanced resolution and dynamic balance of the 600/650. Though I heard most of the differences between the S and S2 in their balances, there are some subtle improvements that I heard in the 660S2’s staging.

The original recorded version has a loose, improvisational feel: the bass and drums hold down the core structure of the songs – with a nice punch where the upright bass and bass drum sync up – while lilting horns add some punctuation. Would these be a good entry level pair of open back headphones or would you suggest trying a less expensive pair at first? It’s an approach that doesn’t seem out of place with classic hi-fi, either, as that’s exactly what Sennheiser has done with its latest headphones, the HD 660 S.

The underemphasized treble of the HD 660 S may be preferable if you find sounds in the higher frequencies particularly piercing or painful, but, for most people, the HD 600 sound better-balanced overall. I also used them in tandem with a range of kit including a Chord Mojo, TC Electronics BMC-2 and a Naim Uniti Atom.