Sennheiser HD 660S2 Review

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Design, Build Quality & Comfort

The new HD 660S2 follows Sennheiser’s classical design and from far you can’t immediately tell the original apart from the new edition. The biggest visual changes are:

– The logo on the grill (gold, not silver)

– The headband and yokes (gold, not silver)

– Missing L/R markings on the outside

– The 3 dots that indicating the left side are now on the front, no longer on the side

– Thicker head band cushioning

The HD 660 S2 is still designed in Germany and built in Ireland, but to me it seems the build quality has gone done a little and the new S2 now seems to be a tad less study. It shakes and moves more but it still is a very well-built headphone.

Sennheiser comfort-wise always scores well and it’s no different here. The velour/plush ear cushions are very comfy and the side pressure on your head is not too high, and it’s evenly distributed. The headphone always stays perfectly in place, but it never is uncomfortable. For some heads the clamping force might be a bit too much, but you can always stretch the headband.

“The velour earpads of the HD 660S2 can only be described as a tactile pleasure. With just the right amount of tension for proper acoustic positioning and supple padding, the headband won’t draw attention away from your music, either”.

The headband with the nice thick cushions evenly spreads the headphones’ 290g weight over the top of your head, so also that part is very comfortable. All of this, combined with the open-back design, gives your ears an extremely comfortable climate, even for super-long sessions.

Both supplied cables measure 1.8m. That’s long and safe enough to move around safely in your office when the headphone is connected to a desktop amplifier. If you plan on using the HD 660S2 on the go, you better find a short replacement cable. Though I don’t see why anyone would listen to open back headphones on the go. All the external sound leaks into the HD 660S2, and all of the music you play will be audible by people close to you. This really is a headphone to use in quiet environments, where you don’t disturb anyone and where you can optimally enjoy the sound quality.

Sound – Sennheiser

I received the HD 660S2 after it was launched, but I have been using it as a daily driver ever since. I have used it with a multitude of amplifiers, tube and non-tube, but I will go deeper in to the synergy part later in this article.

As usual, let’s first look at how Sennheiser describes the ne HD 660S2’s sound.

“An intimate, relaxed sound signature combined with outstanding precision and exceptional comfort — and now, extended sub bass — for a deeply moving experience.”

”The non-fatiguing HD 660S2 gives people who love music an intimate way to connect more deeply with their favorite songs and artists. Breath-taking resolution and precision take you closer than ever to instruments and vocalists. Yet the sound is natural and balanced, never harsh or brash. This warm, inviting signature combined with extended sub bass makes listening uniquely pleasant and rewarding.”

So basically, Sennheiser is emphasizing the HD 660S2’s natural, warm sound, with extended bass and its unfatiguing character.

Let’s dive in further!

Sound – Intro

As the big focus of this review is on the comparison with the other Sennheiser headphones and the amplifier synergy, we’ll keep this part to the point. Testing was done with a series of amplifiers, using the Musician Audio Aquarius and EarMen ST-AMP as DAC, streaming music from Tidal via ROON on my laptop. For the direct comparisons I used the Cayin Audio HA-3A tube headphone amplifier, as it has an impedance selector, and it allows to connect 2 headphones in balanced mode at the same time. All testing was done in balanced mode, unless specified otherwise.

I must admit that I from the start have been really impressed with the HD 660S2’s performance. It’s so easy to listen to and with its excellent comfort, I can easily use it for 7h a day and more. The HD 660S2 also is a do-it-all headphone in my opinion. I of course mostly use it to listen to music, but also for videocalls straight from my laptop. Even watching tv and Netflix is a pure pleasure with this set, as is sounds so natural, effortless, and unfatiguing.

Sound – General

The Sennheiser HD 660S2 sound very open and spacious and it extends well on both sides. The presentation is also nicely airy from top to bottom. While the depth is good, especially in the lower frequencies, the layering over-all could be even further improved. It’s nice but it’s not at HD 800S levels. We don’t expect it to be either, but we know it can be even better. The HD 660S2 has excellent PRaT and a really clean presentation.

The HD 660S2 is a full sounding headphone but it never exaggerates, it does also depend on the amplifier in use. The tonality is very pleasing to the ears with a soft, smooth, and warm character. Also, here the HD 600S2 doesn’t push the limits and the HD 660S2 always sounds very natural and unforced. It’s so easy to listen to with its unfatiguing nature.

On a technical level, the HD660 S2 also scores well. The smoother tonality doesn’t stand in the way of the precision, extension, and overall detail retrieval. As expected from Sennheiser, the dynamics are excellent as well.  Also impressive is the left-right balance and stereo imaging, it’s a joy to the ears. You get a perfect mix of body, cleanness, and precision and that combined with the smooth and dynamic delivery makes it a very musical high-end headphone.

When looking at the HD 660S2’s frequency response, you can clearly see the elevation in the bass region, but also the treble section was tweaked a little upwards (except for the lower dip from 3-5k). It makes the HD 660S2 have more presence as well as more energy on top, but it never feels forced or out of balance. My ears certainly dig this typical tuning.

The article continues on the third page with more on Sound. Click here or use the jump system below.

Page 1: Sennheiser, HD 660 S2, Specifications, Box & Accessories

Page 2: Design, Build Quality, Comfort, Sound pt. 1

Page 3: Sound pt. 2, Comparisons

Page 4: Synergy, Conclusion