Sennheiser has been around since like forever and they’re one of the most respected companies in audio. In the past, Sennheiser has impressed us with a lot of top-quality products like the HD800, the HD 800S and many 5XX and 6xx series headphones. Sennheiser has also upped their IEM game and they have successfully launched the IE 200, IE 300, IE 600 and IE 900 inear monitors.

Maybe Sennheiser would suggest that you can drive this headphone directly out of a smartphone, but I consider it an April’s Fools Day joke. This headphone need the cleanest possible amplification and, of course, a dedicated one. I’ve managed excellent results with an Audio GD Master 9, and also with a HeadAmp Pico Power, and even with the ordinary Pico. The headphone simply comes alive, the dynamics raises your pulse, it’s a completely different story with dedicated amplification. The HD 660 S are a comfy headphone. The soft velour earpieces sit easily around even relatively large ears, and there’s enough padding to stop things getting uncomfortable over longer listening sessions. The metal headband does perhaps clamp the earpieces a little too firmly around the head, but we found that eased off over the month or so we spent with them. And if it does feel too tight, there is an easy fix: you can tease it a little wider by clamping it over a pile of books overnight. Sennheiser HD 660 S review: Sound qualityIn any case, if you like a slower smoother presentation, I think you’d better keep the HD 650 because it does this better. If you listen to acoustic music, jazz or classical, the HD 660 S becomes an obvious recommendation. The 4.4mm cable is likely to spend most of its time in the box: apart from Sennheiser’s own HDV 820 headphone amp/DAC and a vanishingly small number of other devices, this connection standard has yet to hit the mainstream.

When changing the HD 650 with the HD 660S after a non-stop 2 hour listening to the HD 650, I can feel that the veil has lifted, the mid-bass stops rattling and clipping and the harmonic distortion feels lower. Anyway, the superior precision of the HD 660 S is in effect, the model offers the most credible three-dimensional holography of the 3 models.Have you heard the phrase “Sennheiser veil”? Senns are not detail-forward so to many they can sound veiled when they are first put on. It took me awhile to drop this feeling after doing weeks of listening to the likes of the Audeze LCD-24, HiFiMan HE1000V2, and Abyss Diana Phi. However, Senns are actually quite detailed at their price points; they’re just subtle about it. Once that veiled feeling wears off, there’s a fair amount going on. The 660s is no exception here. It’s reasonably resolving in the mids and lower treble in particular. Room reverb, many vocal subtleties, etc. are presented well. Interestingly, despite the fact that I don’t feel the notes flying a few meters from me, I can clearly hear the angle at which they are emitted, a good sign that the holography is in effect.

During my time with them, post the slight bending, I had no issues with having them on my head and listening to them for several hours without any fatigue. They stayed firm in place regardless of my lying position and truthfully, I really enjoyed how they felt on my head (again post bending [which again I stress to do at your own risk]). Perhaps time will break these into the forming sand the HD650 is to me but even if it doesn’t, what’s so wrong with the loving brace of a relative who really misses you? The HD 660 S easily reproduces the entire audible frequency range, from true low bass levels to well above 20 kHz. It features impressive levels of detail resolution and balance, making it a go-to choice for hi-res sound sources of any genre. I think that the HD 660S performs decently well for dynamics. The HD 600-series definitely is not known for being punchy, but I still thought that the HD 660S performed slightly better than its predecessors in this category. It was by no means the strongest out there, but the HD 660S did have some punch slam. I found microdynamics to be fairly well-defined as well, as I felt like all elements in the mix had a fairly good sense of tension and presence. Overall, I would say that the HD 660S perform well in this category, although I do think that other headphones like the Sundara and DT 1990 Pro make for a more engaging and energetic experience in this regard. EQKHz is the peak resonance gain of the ear, the shape of your ear boosts these frequencies strongly. Loud sounds mask other sounds that are close in spectrum, this is called frequency masking. By negating this ear gain, the sound falls much flatter on the eardrum. The result is that everything except this 1-5K area sounds louder and clearer becose the ear resonance is the limiting factor of how loud can you play before it starts being uncomfortable.

Oh ho, here we are. Time to find out rather or not the HD660 S can uphold the claim of it being a successor to the legendary HD650, even stating that “the legend continues” right on the front of the box. At first listen before A/Bing the two side by side I originally couldn’t tell much of a difference just going off memory and thought, ‘ok sweet, they’ve just made a HD650 that’s more sensitive and updated its looks a little bit’. But immediately after popping in ol faithful the differences immediately become apparent. The fit and comfort depends a little on how much time you give them. Out of the box, HD660S is quite tight and their fit is quite tight on the head, and while this might mean that they won't be fully comfortable for any head, it also means that they are pretty secured in place, you can bang your head quite a bit without them falling off your head, and you can do quite a bit of movement without fear that they'll fall. It is a known fact that HD6XX series headphones become quite a bit more comfortable with some wear, and we are able to confirm this, after wearing them for a few weeks they can get so comfortable that you may forget they are on your head. The earpad width is large enough for most ears, but it is quite a bit smaller than that of Amiron, for example, which is quite a bit larger. The earpad material, on the other hand, is really nice to the touch, pretty soft, but with a texture, allowing for an excellent overall comfort. Now, HD660S is not a portable headphone. Even trying to consider them to be one is wrong. We did take them on a little adventure in the Izvor Park in Bucharest to test this, but they still are not quite that portable, they would probably fit best with your favorite desktop and armchair setup. Their design and fit is a little more special than that of the fairly conventional-looking HD 660 S too. However, while I no longer have the HD 700 to hand for a direct A/B test, comparisons with other contemporaries suggest that pair is “different” rather than flat-out better.I would like to say that first and foremost I am NOT an “audiophile” but rather an audio enthusiast. I listen to music to enjoy it. Do I prefer a lossless source? Yes, of course. But I can still be very happy streaming from Pandora or even YouTube's “My Mix” playlist. I also prefer equipment that sounds the best to me personally regardless of what frequency response it has or rather or not it's “sonically accurate” and I always have and shall continue to encourage others to do the same.