[robthemac]

I'm trying to get hold of my previously-owned HD-598 to add in to the mix.

 

[robthemac]

Ok, I'm going to do this slightly differently. I think my impressions on how they sound largely line up with @redrich2000 and most of the other reviewers. Instead of focusing on that, I'll talk more about what Sennheiser I think were hoping to achieve with these, and where I think they sit in comparison to the the rest of of the Sennheiser line-up.

Gear used as part of comparison to the HD-660S:
Sennheiser HD-6XX
Sennheiser HD-800S
Beyerdynamic DT-990
Woo WA-7 + WA-7tp
Musical Fidelity VDAC-II --> Trends Audio PA-10.1D
All gear is in unmodified form.


Aesthetics: pretty standard HD-6** series fare. The darkest-coloured of the above Sennheisers. The grill has been shaped slightly around the 'S' logo, which does add a little aesthetic interest to what is otherwise an aging (if timeless) design.

Comfort: I can't subjectively notice any difference in weight between the 660 and 6XX. The 660 is markedly more comfortable regardless, due to a significantly more gentle clamping force. The recessed bottom section of the pads on the 660 also put less pressure below the ears.

Soundstage: Very close, but the 660 is slightly more spacious than the 6XX. It doesn't near the HD-800S or DT-990, but a definite improvement over its Massdrop brother. Detail retrieval is similar to the 6XX, but the lower treble energy gives the 660 the impression of better detail with things like brush strokes and fingers sliding on strings.

Bass: Excellent definition, but lacking sub-bass extension compared to the more expensive HD-800S. The 660 has a mid-bass hump that gives the impression of 'more' bass, but not necessarily 'better' bass. Very similar compared to 6XX.

Midrange/Treble: There is a spike in the upper midrange and lower treble in the 660 compared the the 6XX. This can sound splashy and uneven, but it also adds some excitement and energy that can be lacking in the HD-6XX. I don't think it's fair to call it 'grainy', but certain tracks do sound harsher on the 660. Treble doesn't extend as far up as the HD-800S, but seems to roll-off less rapidly than the 6XX.


So what should we make of all this? Is the HD-660S a better headphone than the HD-650/6XX? I think that depends entirely on what you are looking for in a headphone.

The HD-650/6XX is one of the best-regarded headphone of all time, as evidenced by it's immense popularity (and sales figures). I am of the opinion that the midrange of the HD-650/6XX is the best of any headphone I've ever heard. It is so even, so smooth, so natural. The HD-650 isn't perfect though, and it can justifiably be criticized as rolled-off or 'veiled' compared to the competition. Whether or not this is a flaw or an advantage depends on your point of view, but for most people most of the time, it will be a flaw. The HD-660S addresses this flaw, and I applaud Sennheiser for doing so. Add some excitement in the upper-mids/lower treble to a slightly wider sound-stage, and for most people, the HD-660S becomes clearly the better headphone. If someone asked me for what one headphone to buy without having a preference for any particular sonic signature, the HD-660S would be my clear recommendation. It gets you closer towards the HD-800S sound, for not much more cost.

However, the headphone community has reacted with less than unanimous praise for the HD-660S. This is because Sennheiser have sacrificed the most beloved aspects of the HD-650 to appeal to a broader consumer audience. The midrange-focused sound and evenness of frequency response have been sacrificed for greater excitement. If you want to hear female vocals or saxophones at their very best and most natural, the HD-650/6XX is the obvious choice. The 660 loses that magic.

If I could only have one headphone in my collection, I would pick the 660 above the 650/6XX. That extra sparkle is worth the trade-off. However, many in the headphone community have different headphones for different purposes. This is why, for me, I would rather have my HD-6XX than the HD-660S. If I want sparkle and treble energy, I have the HD-800S. If I want bass, the LCD-3 will do just fine. The DT-990 has the scooped signature for hip-hop covered. For focusing on mids, the HD-650/6XX fits in perfectly as part of a collection, better than the HD-660S.



In summary, I think the HD-660S is a fantastic headphone that has improved on the most criticized aspects of the HD-650. I'd happily have it as my only headphone, and for this purpose I think it's a better choice than the HD-650/6XX. However, for those of us fortunate enough to have a headphone specifically for smooth, buttery midrange, nothing quite beats the classic HD-650.

 

[robthemac]

Thanks to @Sennheiser and @White Lotus for the loan!

Where should I send it back to?

 

[White Lotus]

Thanks mate!

I'll shoot you a PM.

 

[White Lotus]

The tour has now completed!

The OP has been updated with links to everyone's reviews.

Big thanks to everyone for getting involved with this tour, hope you enjoyed it!

Thanks to Sennheiser for letting us have a listen.

Cheers guys.

 

[Mightygrey]

My week with the HD660s is almost finished-up, I'll be sorry to say "goodbye" to them...I found that they:

- Actually played nicely with an OTL tube amp, my Bottlehead Crack & Speedball, although I suspect the Tung-Sol 5998 power tube might have been a factor as I believe it lowers the output impedance from 120 to around 70+/- ohms
- They also played very nicely with a full 2.6WPC from my Emotive BasX A-100, which still had a nice amount of play at the lower-end of the volume dial

@n05ey - you're up next mate, can you please drop me your best postal address? Otherwise if you're in Sydney I might be able to drop them on Saturday.

Edit - some additional thoughts:

The short version: they’re great, but I won’t be picking them up (at the current price, anyhow).

The short version on the sound stuff: they neatly split the difference between the 580/650, while adding slightly better lower extension.

The 660s makes the 650 sound syrupy, and immediately the clarity and sharpness of the upper treble is apparent. There’s more speed and attack - where the 650’s create a big, warm sludge-y wall of sound on Smashing Pumpkins “Hummer”, the 660s pulls the instruments apart and gives the guitar more edge and energy. There’s less of a mid-bass hump on the 660s, but feels like there’s more dynamics and impact from the lowest register.

The 660s is more similar than different to the 580’s. The 580’s sound altogether thinner and more precise, with less bass extension. I’m rocking a pair of Dekoni fenestrated sheepskin pads on them at the moment which make the sound ever so slightly more bright/cold, but feel amazing.

The 650’s are best for saxophones, some vocals, and relaxed listening.

The 580’s are best for acoustic guitars, most vocals, and detail.

The 660s’s are the most balanced top-to-bottom, but don’t really have the same charm that makes the other two unique. Having said that, if you’re looking for a bullet-proof recommendation for open-back hifi cans that do pretty much everything brilliantly, and are all-day comfortable, I’d have no hesitation recommending the HD660s’s.

If you own the580/600/650 others, relax - you have a great set of cans and aren’t missing out on any musical enjoyment.

One gripe about the 660’s - it’s pitched as being “easier to drive on portable devices” at 150 ohms impedance, but comes with two super long cords: 1 x 6.3mm terminated (with 3.5mm adapter) and 1 x 4.4mm pentaconn terminated. Pentaconn devices are few and far between, and certainly not on my immediate shopping-list. I’m all for innovation and trying to create a better industry standard, but it’s just not a problem that needs solving - for me at least - right now. Why there’s not a 3-foot 3.5mm cord included (like with my HD650s that were bundled with the Apogee Groove) is beyond me.

Lastly, there’s probably OTL tube amp owners (like the Bottlehead Crack) out there who probably aren’t interested in the 660s due to its lower impedance, that’s not as good a match with the higher output impedance of OTL tube amps. I was pleasantly surprised to find that the 660s played very nicely with my Crack + Speedball, perhaps because the Tung-Sol 5998 power tube reduces the output impedance from around 120 to 70-something ohms (as far as I know). More of an interesting anecdote than a revelation, but hey - it might be interesting to you.

Cheers!