High-grade 38mm soft diaphragms with steel mesh damping material and vented magnet system for clean, low-distortion sound.

Iconic headphone design with an updated sound tuning

Meet the newest version of Sennheiser's legendary "HD 600" series. The HD 660S2 headphones sport a similar look and feel to their predecessors, but offer some sonic tweaks. From early listening impressions — and my time listening side-by-side with older "600" models at CanJam NYC — I enjoyed the deeper bass extension and slightly larger soundstage.

These open-back headphones offer the intimate, forward sound presentation that the "600" line is known for — versus the more spacious soundstage from the angled drivers of Sennheiser's 560S 'phones. But it stretches a tad further outside the head, giving some space to really appreciate the separation and sense of direction offered by quick-moving dynamic drivers. Mids and vocals come throught distinct and realistic, while the highs are at once smooth and vivid in that way Sennheiser can expertly pull off — clarity without too much sizzle.

Our "most comfortable audiophile headphones"

Years ago, we did a deep dive on headphone comfort and asked 20 employees to test and score over 50 popular headphones. The original HD 660S was named our most comfortable set of audiophile headphones. Sennheiser has only slightly tweaked the design here, softening the headband padding that hugs the crown of your head.

Velvet-soft ear pads hold the HD 660S2 headphones into place without squeezing too tightly.

While the HD 660S2 features larger earcups than most “general purpose” headphones, the weight is distributed nicely. Our testers said that the previous generation felt lighter than other large audiophile headphones. The velour ear pads press gently on the side of your head and give your ears plenty of room to breathe.

They also fit snugly and stay in place well. And we learned that "security and stability" were the most important comfort and fit traits to our testers.

Several ways to connect

These headphones include two cables, one with 4.4mm balanced headphone plug, which has become the new industry standard connection for balanced headphone operation. I've found that the thumb-drive-sized iFi Audio GO Bar DAC/amp combo pairs up really nicely with the HD 660S2 'phones.

Since the headphones are 300 ohms, I thought I might need a larger, heavy-duty amp to drive them. But I found the GO Bar offered plenty of power and gave me more incremental control over the volume than the larger desktop amp I had on-hand. The iFi/Sennheiser combo delivered that classic immediate HD 600 sound signature — but with an extra level of depth.

(For more traditional headphone connections, Sennheiser includes another cable with an unbalanced 1/4" plug and a 3.5mm miniplug adapter.)