Sennheiser HiRes Audiophile Headphone (HD 660 S)

Product Information

Chord says that their products have good USB isolation and noise filtering, so no, unless you really want to spend money on a USB cable, and it would make you feel better, there would be no audible or measurable difference from using a different cable. There's also a big difference in soundstage, as the HD 800 S create a wider, more out-of-head audio experience. My hearing quirks include a high sensitivity to midrange frequencies from just under 1KHz to around 3Khz, give or take. The HiFiMan are more comfortable to wear for a long period of time and they also have a more accurate sound profile. The Sennheiser HD 600 and the Sennheiser HD 660 S are similar headphones overall, but the HD 600 are a better choice for audiophiles who prefer a more neutral sound profile.

I spent weeks feeding the HD 660 S with a hugely varied playlist stretching from Bjork to Wagner, and Ed Rush to Fleetwood Mac, and across everything from vinyl to CD to hi-def audio via Tidal’s excellent streaming service. I don’t use the crossfeed on Roon, but I use it on the Mojo 2, I set it at max (dark blue light), but I cannot hear any instruments separation difference. On its product page, Sennheiser claims 104dB/Volt for the HD 660 S; in its manual, Sennheiser say the HD 650 has 103dB/Volt sensitivity. What you’re hearing is probably that natively high-re tracks so far tend to be be mastered somewhat better than your average mass-market CD. Thanks to an aluminum voice coil, the 38mm diaphragm remains nimble for ultra-quick impulse fidelity across the board.

The HD 660S comes in a matt black and anthracite design – a high-end aesthetic that embraces both contemporary style and timeless elegance. However, if you have a stand-alone mic and play in a quiet room, these are quite comfortable for long gaming sessions and they have a good sound quality. Right away I will say that these are my favorite headphones in Sennheiser’s line-up, and for the music that I listen to the most (classic rock), I really, really enjoy them.

I mentioned earlier in this review, that I considered value a very important factor when talking about the HD 660S.The HD 560S have a better-balanced bass and treble range, a more natural soundstage, and a more comfortable fit. The HD 650 is a bit too warm sounding for me (just a bit), and the HD 600 is my favorite of the two. However, as mentioned before, the 660s handles vertical space much better than 6XX, creating a much more convincing sense of soundstage height. In the 300Hz square wave responses above you can clearly see the HD 660 S response (middle) is very much like the the HD 600 response (top) and is quite unlike the HD 700 response (bottom).

I've also seen a post where a Head-Fi made an inquiry to Sennheiser about whether the HD 600 or HD 650 would be discontinued.

Update: 08/12/2019 After comparing these headphones with other models, we found them to be very tight and reduced their score accordingly. On the other hand, some may find the HD 58X Jubilee to be very tight and not as comfortable as the HD 660 S. Thanks to their mostly-plastic construction, these are extremely light (only 260g or so), so I doubt anyone will have weight issues with these. But all things considered, I can’t help but feel like the 660S sold itself a little too short in its lows, teasing me with trace moments of rumble.

Disclaimer: The Sennheiser HD 660S was sent to us by Sennheiser directly in exchange for this review. I think Roon will upsample the convolution if need be, but if there are already correct ones, might as well give them to Roon. Were it any other maker producing the HD 660 S I would have been quite impressed with how close they managed to get to the sound of the legendary HD 600/650. The joints where the headband meets the yolks feels fairly fragile and seems to be the weak point of the build.Something tells me that the S2’s treble balance is going to be the most divisive change that has been made.