It’s here that the extra meat down low and the warmer midrange do a far better job of driving the music without feeling overly lightweight or clinical.

Well they sort of state that it's a new design, but I'm betting that's a bit of poetic license—the HD 700 is a relatively new design.

These phones can play 8K videos, so I don’t think it’s the bandwidth capability is what they mean by these Hi-Res numbers. I'll not wax poetic this time regarding the long and storied history and my experiences with the HD 6xx family of Sennheiser headphones. Sennheiser packed your HD 660S with a versatile set of essential cables, each one impedance-matched with ultra-low capacitance.

He's a big fan of tube amps and custom inear monitors and has published hundreds of product reviews over the years. Thought there’s a little more low mid amplitude and warmth with the S2, I perceived this extra boost as an extension of the changes made to the low end rather than significantly changing how I heard the mids balance proper.For this sound section I will be going over the HD 660S’ tonal and technical performance while drawing comparisons to some of its competitors, as well as some of Sennheiser’s other offerings; namely the DROP X Sennheiser HD 6XX and HD 58X Jubilee. But, it’s not a completely different headphone on a tube in the way that its 600 and 650/6XX brethren are. This means the leakage will be fuller sounding compared to that of closed-back headphones and in-ears. The Sennheiser HD 58X Jubilee are slightly better critical listening open-back headphones than the Sennheiser HD 660 S. He's fairly privy to inside information, and a good hard look at the two make it fairly obvious they're related.

The Amplifier/DAC used in this review was the JDS Labs Element II connected via USB to my desktop computer.My hearing quirks include a high sensitivity to midrange frequencies from just under 1KHz to around 3Khz, give or take.