Bass, Mids, Treble
I’ve seen a couple of people describe the Sennheiser HD660 S as having only a very light bass, and to me that shows they definitely didn’t try the HD660 S with different sources and/or even the balanced cable. Bass, depending on the amplifier and connection used, goes from neutral and fast to bigger bodied and more romantic. Some might not like the bass dependency but I actually think it’s a good thing as you can make the HD660 S’ bass sound like you want it to sound. In both cases bass has great detail, nice layering and good depth.
It’s more or less the same story when it comes to the mids. They go from fast and precise with a little lighter body, to a thicker mid presentation that’s a bit slower yet smoother and very rich. The mids in both cases have excellent timbre and detail and just like with the HD650, the mids are oh so important in the HD660 S. You either like the typical Senn mids or you don’t but to me they’re musical, rich and well layered with a natural tonality.
The treble section in single ended mode – and from more neutral sources – sounds energetic, neutral and fast. Some might even find treble to the brighter and more forward side but treble is nicely extended, clear and crispy. With warmer sources and in balanced mode, you get a softer and maybe more natural sounding treble, still with good energy and lots of detail. Of all 3 Senn headphones, the treble on the HD660 S might be the most particular, something that’s noticeable in the FR chart as well.
If you’ve been reading up about the HD660 S on the web you might have come across some statements about the HD660 S graininess. While I do see what they’re pointing at – especially when coming from the MX-4 – I can’t really say it bothers me this much. Is the HD660 S the “leanest” of the threesome and the most difficult to get right? You may have a point there.
Sources / Amplification
An important point with the HD660 S is that it is easier to drive than the other, 300Ohm, Sennheisers. While this is a fact, you will still see the volume going up on your source when coming from a really easy to drive headphone. And it doesn’t stop there as the sound signature from the HD660 S really depends on the source you’re using it with. Like its brothers, the HD660 S scales up nicely with a good and powerful desktop sized amp, though it also sounds more than just good when connected straight to a DAP. In that regard the new HD660 S is a little less “upscaling”. I would still suggest using a dedicated amplifier however as it just lifts up the HD660 S’s performance, and basically Sennheiser is saying the same thing:
Offering a lower impedance of 150 ohms, the HD 660 S can be enjoyed with HiRes mobile players or when directly connected to high-quality, stationary HiFi components. They fully reveal their potential when connected to the balanced outputs of a dedicated headphone amplifier such as the Sennheiser HDV 820 or to the balanced output of a mobile digital audio player.
Ever since the Headonia and Solaris were added to my main headphone system, the Violectric V281 doesn’t get as much play-time as it used to. The Vio V281 is the only solid state amp left in my setup and I really should listen to it a lot more, as it is an exceptional performer. Both the older HD6-series sound great in combination with Violectric amp(s) and so I had really high hopes for the HD660 S as well. The V281 didn’t disappoint and you get a full bodied, still nicely paced bass with good depth. The mids also have good body and the treble section is a tad softer as you’d expect from the V281. The only point where the V281 in single ended disappoints a little in combination with the HD660 S, is with the spaciousness and sound stage. If you’re familiar with the amplifier however, this shouldn’t come as a surprise.
With the Astell&Kern Acro L1000 you get a fast, neutral presentation with somewhat lighter bass, but with excellent speed and precision. Treble for some might be a little too spoken out but the mids are still lovely detailed and precise. It’s not a great source for the HD660 S but it certainly isn’t a bad source either.
When switching to the more neutral tuned Auris Audio Headonia 2A3 tube amp, you get an overall more energetic sound with a higher pace and more forward upper mids and treble. You also get deeper/tighter bass, more neutral and fast paced mids with slightly more forward voices and more top end extension and clarity. Treble becomes more energetic but I’d not label them as bright per say.
The warmest and smoothest HD660 S shows up when paired to the AudioValve Solaris tube amp. It’s a softer and romantic sounding amplifier and the HD600 S immediately shows that. You get a smooth and rich sound with more impactful bass (great layering!), thicker/warmer musical and natural mids and softer yet extended and rich treble. The musicality here is high and the HD650 fans will for sure prefer this combination where the HD600 fans will probably prefer the Headonia as source. The V281 is the perfect amp for those who want it to sound a bit like both.
The Astell & Kern AK70ii is a complete player with a warmer sound but one where the musicality level is very high. It especially are the vocals that jump out in this combination and you get a good amount of bass, a good pace and soft treble but the mids aren’t the thickest overall. While this combination certainly isn’t bad, it doesn’t really “do” it for me either as bass is undefined and energy is missing overall.
The TOTL Astel&Kern SP1000 is a more neutral tuned player, with a very high level of detail and a focus on the upper mids and treble region. It has a fast pace, tight bass and great clarity and with the HD660 S hooked up to it, the combo sounds really good. Tight, powerful bass. Excellent clarity and speed. Rich, clean mids. A wide sound stage, etc. If you prefer warmth and smoothness (or the typical HD650 sound), you might find the sound a little too energetic and forward however. In that case the NW-WM1Z is more up your alley.
With the Sony DAP, even in single ended mode, you get a warmer, slower sound which also is very musical. You get bigger bass, thicker mids and soft yet detailed treble. The overall level of detail is high and the Sony/Senn combo shows great layering. Switch to balanced mode and the bass becomes impressive, the mids even smoother and the treble softer. This is the ideal DAP if you’re looking for that HD650 sound signature. The SP1000 is more comparable to the HD600 for that matter.
With Chord Electronics Mojo (AK70ii as source), you get a very fast sounding HD660 S with great detail and extension. The focus here is more on the upper mids and treble as well (like with the SP1000), but it’s softer and smoother in presentation with great vocals. Bass is lighter in body and impact but it is good in quality. Treble is energetic but not the furthest extended. With Chords Hugo 2, you get a higher resolution and more extension with improved depth and layering. The pace is still fast and you get a clean, more to the neutral kind of sound, yet with a slightly smooth touch to it. Bass has more quality with better depth and layering. This also is valid for the mids yet the upper mids and vocals still have that focus on them. The treble end is more extended compared to the Mojo and it has more energy, and might come of brighter to some. Personally I prefer the Chord Hugo 2 with the HD660 S as it lifts the Senn up to a higher level.
I have to say I was positively surprised with how musical the HD660 S sounded straight from my laptop. Sure bass impact and body was on the lighter side, but it was tight and punchy. The mids were rich and the treble energetic. The voices were more up to the front but not in a way that it becomes annoying. It’s an excellent emergency setup, let’s put it like that.
In the end it is clear that the HD660 S can indeed be reasonably easy driven by a portable source, but I still prefer a full sized desktop amplifier. My personal preference goes to the Solaris, while in portable mode, the WM1Z in balanced mode holds my preference.
Is the Sennheiser HD660 S a good headphone? Absolutely! Is it a great headphone? Yes, with the proper source it definitely is. Is it as good, if not better than the HD600 and HD650? Well, there it becomes more difficult. The HD660 S is a great headphone if you want a bit of both the HD600 and HD650, but in my personal opinion it won’t ever be as iconic as the HD600 and HD650 already are. In 10 years’ time people will still be talking about those two Senns, but I’m not sure they’ll remember the HD660 S. Only time will tell if I’m right or wrong.
It is a fact that the HD660 S now is easier to drive, and it performs really great with the Sony WM1Z in balanced mode, but the headphone still scales up nicely with a good desktop sized amp, yet not as much as before.
I have been using the HD660 S for about 3 weeks non-stop now in my office and while I liked it from the beginning, I like them even more now. So yeah, the HD660 S is a job well done and it will please a new group of listeners that couldn’t find their ideal sound signature in either the HD600 and HD650. I don’t think that those who love their HD600 and HD650, will be replacing their beloved headphone for the HD660 S, but if you have to start from zero, the HD660 S might just be that one for you with a bit of the best of both worlds.