Sennheiser HiRes Audiophile Headphone (HD 660 S)

Product Information

In conclusion, I don’t recommend you to plug them directly into a smartphone, but if you add a portable amplifier to the mix, things will get radically better. There’s little-to-no sound isolation here, so don't take these headphones with you on your commute. (Image credit: Future/TechRadar/Henry St Leger) Sennheiser HD-660S2 review: Price & release date This problem is no longer present on the HD 660S and this is probably one of the best improvements of the new model. 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.

In the treble range, the headphones deliver transparency and detail resolution that gives the sound a brilliant that can only really be found in the high-end price range. Percussive details or small echoes you’ve not heard before can be discovered with glee here. In addition, the HD 660 S certainly shows the limits of a production. Room, Dynamics, Levels In this, and the following series of photos, the HD 600 is at left, the HD 650 at center, and the HD 660S is to the right. 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. My final thoughts on the HD660 S is that I believe that Sennheiser is making a mistake in calling it a successor to the HD650, for to me it’s not. The HD660 S is a great headphone but it’s its own personality and presents audio in its own way that I believe is way too different for it to be considered a successor. The HD800 S, to me, is the definition of what a successor is. But as an individual headphone the HD660 S is wonderful and a real treat to listen to. I do like how it can be played more friendly off mobile devices however I will say that in doing this Sennheiser has really handicapped the HD660S’ ability to scale. It still shows improvement when listening to top tier gear over a mobile phone but NOWHERE near the legendary degree that the HD650 can. For this sound section I will be going over the HD 660S’ tonal and technical performance while drawing comparisons to some of its competitors, as well as some of Sennheiser’s other offerings; namely the DROP X Sennheiser HD 6XX and HD 58X Jubilee. BassThe HD 660 S features a new transducer design developed by Sennheiser. This results in improved control of the diaphragm movements thanks to a specially manufactured precision stainless steel fabric, which is adapted to the contour of the diaphragm. Extremely light aluminum voice coils ensure the highest impulse fidelity. Unlike the Momentum series, which has punchy sub-bass as its calling card, the HD 660 S have tightly-controlled bass. The frequencies are there, but so is the reserve expected of a higher-end headphone. To make up for this, the headphones delivers a little more power from fairly up-front mids. Everybody shits on HD660S, I think its best sounding out of the box headphone I ever tried, I absolutely love that frequency response! Renowned for their neutrality and musical delivery, Sennheiser’s HD 660 headphones have a cult following. Now in S2 form, the updated model features lighter voice coils and improved airflow, helping to enhance the bass response. Dropping from 110Hz to 70Hz, the bottom end now has noticeably more impact, without spoiling the headphone’s legendary sonic precision. The HD 660 S is designed for more demanding music enjoyment at home, while also allowing for professional audio applications, such as mixing and editing tasks. What’s New?

Yeah, it’s a Senn 6?? series, so we gotta talk about tube amps. At 150Ω, the 660S is basically the minimum impedance that makes sense to use on an OTL (output transformer-less) tube amp. Unfortunately, I don’t have a true OTL tube amp, I have the transformer-coupled Cayin HA-1AMK2. The 660s did indeed sound better on the 1AMK2 than it did on the Atom, Liquid Spark, or Asgard 3, but I don’t think that had much to do with it being a tube amp and the 660s taking well to tubes. If anything, it’s because the 1AMK2 is on a much higher performance tier than any of those amps. The truth is, the 660s did not change its sound much. Yes, there was slightly more detail and an improvement in overall technical performance, but there wasn’t the transformation that happens when the 6XX is put on a tube. So, you can use the 660s with a tube. It does change a bit. But, it’s not a completely different headphone on a tube in the way that its 600 and 650/6XX brethren are.It comes with…the same exact cable connectors as the other two. In a way, I’m sure this is appealing to longtime fans who have spent on aftermarket cables that they’d like to carry on over – but the connectors on these are some of my least favourite available for any headphone. While both previous iterations of theHD 660 are regarded as modern classics amongst Hi-Fi heads, the need for a tweaked version of what many feel was aural perfection shows what a discerning bunch audiophiles are. The HD 660S comes in at an impedance of 150ohms and a sensitivity of 104dB. I personally found them to have plenty of volume on most devices I tested, like my MacBook Air and Nintendo Switch. However, I did think that they sounded better when being fed power from my amplifier. When running them on devices without a discrete amplifier I thought that they sounded a little more compressed, so I will list an amplifier as recommended for these. Still, these are very efficient, so it does not have to be a very powerful amplifier. Amplifiers like the Liquid Spark and JDS Labs Atom will be more than enough to drive these very cleanly. While we don't know Sennheiser's input in Equalizing their headphones, we always provide those were we're able to. The main thing that we felt would be welcome to add to Sennheiser HD660S was a touch more bass (and a lot more bass for certain music types), along with more treble. Happily, the Sennheiser driver technology is quite good and it can be equalized quite a bit without losing definition and without introducing distortion. 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.

I’m also glad to see that Sennheiser after a few years will finally be present again at the High-End Munich show. The Sonova takeover surely has something to do with that. I for one look forward to visiting the new Sennheiser booth in Munich next week.

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. The comfort while being worn for long periods of time is very good, and with HD660S, you can walk and even to some heavier exercise without damaging them, or without feeling any fatigue, and it surely is possible to wear them for prolonged periods of time without much issue, but you should mind the cable, which is quite long. There are no microphonics, and no other issues we were able to notice, but HD660S does not isolate from the outside noise (at all), and most music being played through them will also be heard outside, so they are quite open in this aspect. How close is the guitar with the 660S! It's exciting but there's less sense of distance of the stage. Nevertheless, the timbre of the strings are exciting, albeit slightly resonant on the lower end, while the 600 has a more "acid" sound. The reverb of the recording venue is more evident in the 660s. The highs presented themselves clean and airy, with a good balance between technical show-off and naturalness. The highs are somewhere in the middle, not overly natural, but also not overly bright and sibilant. 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.