They all aim for clarity, but just like camera makers, each premium headphone brand brings its own flavor to 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 which can sound more “clinical” or sharp and cold, there is a softer grit in the mids and highs, while still allowing full distillation of all frequencies. (The claimed total frequency response is 10 Hz to 41.5 kHz.)
The 660S2 builds on this sound with an extra drop of amber in the sound, for an even more saturated coloration that is most pronounced in the low end. The bass may be the main reason to consider them over the more affordable models in the series. Dropping the needle on hip-hop and electronic tunes releases an extra surge of fundamental power, and it can be a lot of fun to listen to.
The main groove of Biggie’s “Hypnotize” is a laser punch 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 more jazzy flavor. Likewise, Too Short’s “Money in the Ghetto” has a soft punch on the main kick that is skillfully articulated. These aren’t my usual go-to tunes for this type of headphones, but they helped set the stage and sounded great.
The Chemical Brothers’ “Go” is an even more intriguing test, again showcasing the 660S2’s bass skills while emphasizing their lightning-fast transient response. The song’s bass drum is sculpted with a deep echoing reverb texture that expands like a bubble in the center of the image. Excellent instrumental spacing lets you freely roam the dimensional soundstage, from the synth that sweeps across the stereo image before the chorus to the buildup to instrumental breakdown that sounds like an impending rocket launch.
Even the bass drum in Maxwell’s Silver Hammer has a bit more noise, delivering a louder, yet still refined ride than you’ll get from others in the HD 600 series or beyond. I prefer the more neutral grip of the 6XX for such tracks, but it didn’t hurt the experience.
Elsewhere you get the same kind of lyrical clarity and refinement that first made me love the HD 6XX. Reverb tails echo in oblivion; piano tracks allow you to estimate both room size and mic placement – the nerd in me was asking, “Was that a close-up with an open lid of a grand piano abstracted with the room mic?” (I think it was). ELO’s distorted guitar is so textured and visceral it gives me the fibrous, cold crunch of biting into a popsicle.
Even podcasts are more richly represented, letting you hear not just how close vocals are to the mic beat by beat, but deeper details like Sean Hayes had dairy before the Unintelligent Interview with Jon Favreau (he certainly did).
Everything is, in a word, glorious. But to my ears, the HD 660S2 isn’t so much an improvement over other headsets in the series as a slightly different take. Fabulous headphones, I’m mostly interested in the best value for money. As I write this you can get the original 660S at $320not to mention the incredibly affordable price 6XX at $219. Additionally, I found the 6XX to be the more comfortable of the two I’ve tried, which is a major consideration for extended listening sessions.
If you’re enthusiastic about the extra bass, richer saturation, and even tighter flex on your noggin, there’s an audiophile marvel to be had in the HD 660S2. Whether it’s worth the extra coin is up to you and your wallet.