Listening to the song Strunga from the album Mugur de Fluier, I notice the impressive soundstage that is well expanded in all directions. If you carefully listen to fast electronic music on the HD 650 or HD 600, you can hear a micro-echo, like an unpleasant resonance, maybe and effect of the over-damping behind the diaphragm (again just a guess). This effect damages the delimitation of notes and each individual sound end up not being sufficiently well defined. Moving down the headband still features it very nice and firm size adjustments that leave no doubts to the user what the cups have moved to a different size, for each adjustment is made with a notable pop. On that note, this headphone has more adjustment sizes than I think anyone will need. Unless you’ve a really tiny head, you’re more than likely to find the optimum adjustment out of this headphone. Yes, the HD 660S has more resolution and clarity. It still cannot touch the HD 800 in this regard, but I’m happy that things evolved to this high level for the modest price compared to other models that we’ve reviewed.

I now realize that none of the models in the HD 6xx series, including HD 660 S, offers a convincingly large and expanded enough soundstage. The soundstage is somewhat compact and intimate, but surely not claustrophobic. I would categorize it as a medium-sized soundstage, not too large (like HD 800), but also not so close as to make me feel on the stage with the band.Even though the majority of the HD 650 users might say that it excels in the bass department, I am of a different opinion. The performance of the 660S is really remarkable: it's punchier, more contrasted and extended than the HD600. (the sound of the cymbals is timbrically almost "suffocated" in the 600, while it's exceptionally harmonically resolved in the 660s, in absolute terms). The "on-stage" feeling of the 660S does a good job here. The 600 is very nice, but can't really compete with the 660S here. The padding in the new HD660 S feel very firm to the touch and offer a really nice level of both give and support. This may be because these are a brand new pair and my HD650 is, how should I say, well experienced, the padding looks to be a little bit deeper than my ol faithful HD650. This is a good thing because my ears no longer touch and rub against the cloth covering the drivers. I want to mention that, from the 3 models, the HD 650 scaled the worst in this regard. I can feel myself distracted by the micro-echo and harmonic distortion in the bass and mid frequencies, and the slight veil over the notes also impairs the listening experience. By comparison, the HD 600 seems to bring a fresh breath of air and doesn’t have as many shortcomings.

Sennheiser HD660S vs Sennheiser HD600 - Sennheiser vs Sennheiser, HD660S feels like a more natural, more refined, more mature, and better looking version of the original HD600. It is easier to drive the HD660S, and it will fit in most situations where HD600 won't, but HD600 still has the crown of being the fastest of the HD6XX series from Sennheiser. Supplied with balanced and non-balanced cables, the HD 660S2 maximises the potential of dedicated headphone amps and music players fitted with balanced outputs. Balanced cables minimise interference, enhancing the music’s purity. The standard, non-balanced cable is fitted with a 6.35mm plug, with a push-on 3.5mm adaptor also supplied.Everything else is left at default, the master is usually brought at least at -7dB to avoid clipping. The HD 660 S has been created to enjoy music in supreme quality and from many different audio sources. Thanks to its low impedance it also offers reference-class fidelity with hi-res mobile players. Naturally, the HD 660 S reveals its full potential when it is connected to the balanced outputs of a dedicated headphone amplifier such as the HDV 820 or to the balanced output of a mobile digital audio player. Accordingly, it comes with a choice of cables for just about any occasion. All cables are made of highly conductive OFC copper, featuring very low handling noise and sturdy para-aramid reinforcement. The Sennheiser HD 660 S are comfortable, have a great soundstage and a non-fatiguing combination of clarity and rich tone. As stated before, the 660s has a very mild and somewhat rolled-off-at-either-end v-signature. The 6XX has a neutral-warm signature that is also somewhat rolled-off with mediocre extension both high and low. The DT880 is neutral-bright with excellent bass and treble extension but also somewhat lean bass. The amount of treble in the 660s is between the 6XX and DT880, but closer to the 6XX than the 880. The 660s and DT880 are quite similar in midrange quantity. The 6XX and 660s have similar amounts of midbass, being slightly more than the DT880, but the DT880 has the extension advantage and more subbass presence overall, despite it being somewhat lean in the lows (at least compared to its treble). I think the DT880 also has more bass punch/slam. It’s more dynamic. I wouldn’t say it has great punch/slam because of the lean-ness of its bass, but it is overall more energetic and aggressive throughout the frequency range than either Senn. Lastly we’ve the DETACHABLE cable. The cable on the HD660 S is the same that’s on the original HD650. It’s a decent quality cable. It’s not shielded or looks anything fancy but it does its job very well. To my ears there’s no microphonics or interference that I’ve ever heard during my time with either units.

The bass of the HD600 is the most muted of the three headphones and it remains largely in its own camp and doesn’t intrude like the HD650 can at times. There is still a heft in the low end of the headphone that doesn’t completely eliminate the sensation of bass, but it’s hardly ideal for genres dependent on slam and rumble – for which the HD660S is a better choice. Overall impact is also less frantic than the HD660S, but seems slightly more pronounced than the HD650. The sub-bass rumble in Why So Serious? is also weaker and less controlled than the HD660S, but the instrumental has a certain sheen around it that is interesting. It’s not smoothed, like the HD650, but it’s definitely a softer and less harsh experience than the HD660S during the crashing moments. So I really like the mids on the HD660 S and I think when considering the this headphone its own headphone, I believe most will as well.

The new HD 660 S lets you enjoy sophisticated audiophile sound in even more listening situations. The successor of the legendary HD 650 excels with the improved performance of its new transducer design. Thanks to its lower impedance, it delivers reference-class sound also when connected to hi-res mobile players, thus offering much greater versatility. The HD 660 S is an elegantly designed piece of high-quality engineering that indulges the demanding listener with aural precision and great wearing comfort. There is room for improvement, however. While the HD 660 S warmer, more meaty sound works wonders with a lot of material, I couldn’t help shake a feeling that something wasn’t quite right in the treble department. TheHD 660 S2's upgrades look like sensible ones, butSennheiser nevertheless has a big task on its hands as it tries to satisfying the fussiest demographic of music lovers. The sonic performances of HD660S are quite impressive, as much as you'd expect from a successor of the highly acclaimed HD650 and HD600. Prices valid in stores (all including VAT) until close of business on 29th November 2023. (Some of these web prices are cheaper than in-store, so please mention that you've seen these offers online.)