They’re all aiming for clarity, but much like camera makers, each high-end headphone brand puts its own flavor on the experience. Fans love Sennheiser’s HD 600 series not only for their remarkable definition and dynamics, but also for the subtle way in which they express those revelations. Unlike some headphones that can sound more “clinical” or sharp and cold, there’s a smoother grain to the midrange and treble, while still allowing for full distillation of all frequencies. (The claimed total frequency response is 10 Hz to 41.5 kHz.)
The 660S2 build on that sound with an extra drop of amber in the sound, for even more saturated coloring that’s most pronounced in the low end. The bass may be the biggest reason to consider these over more affordable models in the series. Dropping the needle on hip-hop and electronic tunes unleashes an added rush of foundational power, and it can be a lot of fun to listen to.
The main groove in Biggie’s “Hypnotize” is a laser stick of thump with exceptional balance. It’s a funkier sound than the boom you’ll get from cheap bass bombers, almost rewriting the overall feel with a jazzier flavor. Similarly, Too Short’s “Money in the Ghetto” has a sweet, push-button punch to the main kick that’s expertly articulated. Those aren’t my usual go-to tracks for these kinds of headphones, but they helped to set the stage and sounded great doing it.
The Chemical Brothers’ “Go” is an even more intriguing test, again showcasing the 660S2’s bass skills while also highlighting their lightning-fast transient response. The song’s kick drum is carved with a deep texture of echoed reverb that expands like a bubble at the center image. The excellent instrumental spacing lets you roam freely through the dimensional soundstage, from the synth that sweeps through the stereo image ahead of the chorus to the build-up at the instrumental breakdown that feels like an imminent rocket launch.
Even the kick drum in Maxwell’s Silver Hammer has some extra thump to it, providing a more raucous, yet still refined ride than you’ll get from others in the HD 600 series or beyond. I prefer the 6XX’s more neutral take for such tracks, but it wasn’t a detriment to the experience.
Elsewhere, you’re getting the same kind of lyrical clarity and refinement that first endeared me to the HD 6XX. Reverb tails echo into oblivion; piano tracks let you estimate both the room size and mic placement—the nerd in me was asking, “Was that an open-lid close-up of a grand summed down with the room mic?” (I think it was). The distorted guitar in ELO’s is so textural and visceral, it gives me the cold fibrous crunch of biting into a popsicle.
Even podcasts are more richly portrayed, letting you hear not only how close the voices are to the mic beat by beat, but deeper details like whether Sean Hayes had dairy ahead of the Smartless Jon Favreau interview (he definitely did).
It’s all, in a word, glorious. But to my ears, the HD 660S2 aren’t so much an improvement over other headphones in the series as a slightly different take. Fabulous headphones all, I’m most interested in the best value. As I write this, you can get the original 660S at $320, not to mention the shockingly affordable 6XX at $219. What’s more, I found the 6XX to be the comfier of the two I’ve tried, which is a major consideration for extended listening sessions.
If you’re excited about the extra bass, the richer saturation, and even the tighter flex on your noggin, there’s audiophile wonder to be had in the HD 660S2. Whether that’s worth the extra coin is up to you and your wallet.