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Hands-on with Sennheiser HD 660S2
Hands-on with Sennheiser HD 660S2 Jeff Li/IBTimes US

When you ask an audiophile about their favorite headphone setup, more often than not, they will show you a collection of headphones instead of naming just one. What's even more surprising is that not all of their "favorites" will be considered "high-end" in terms of cost. There are always a couple of affordable "mid-tier" headphones in the mix. These headphones may not be top-of-the-line, but they possess their own unique characteristics that cannot be replaced or surpassed by more expensive options.

One of the headphones that consistently appears on people's favorite lists is the Sennheiser HD 600-series, and the HD660S is one of the best-sounding mid-range open-back headphones that we have reviewed. The headphone produces exceptional sound quality when paired with the right sound source. In our case, we used the FiiO K9 Pro AKM edition, which produced one of the most organic and clean sound characteristics that we have ever tested.

So when the Sennheiser HD 660S2 was released, there was an obvious excitement in the office. The question on everyone's mind was whether the German audio tech company could top what was already a masterpiece. Let's dive in to find out.

Hands-on with Sennheiser HD 660S2
The HD 660S and 660S2 are almost identical aesthetically Jeff Li/IBTimes US

Almost Identical Twins

There is already a close resemblance between the Sennheiser HD 600 series headphones, and the HD 660S and 660S2 are practically identical. Upon closer inspection, there are only very minor differences, such as the fabric covering the headband cushion on the S2 being finer and the logo being smaller and in gold instead of silver. Other than these cosmetic differences, no other changes can be observed.

Hands-on with Sennheiser HD 660S2
HD 660S2 proudly wears the mark: "MADE IN IRELAND" Jeff Li/IBTimes US

One difference that goes beyond the aesthetics is that the HD 660S2 proudly bears the mark of "MADE IN IRELAND," while the HD 660S is made in Romania but is not marked on the headphone. While it may be important to some people where their headphones are made, in terms of build quality between the two headphones, there is no discernible difference.

Hands-on with Sennheiser HD 660S2
The Sennheiser HD 660S2 looks to balance the sub-bass and the sparkling high end that's so iconic in the original 660S Jeff Li/IBTimes US

Sound Quality: A Game of Balance

After testing the Sennheiser HD 660S, we awarded it the IBTimes Exceptional Value without hesitation because of its natural and transparent sound characteristics when paired with the right amplifier. However, if there was any complaint I had for the original HD 660S, it would be that it was not suitable for all genres of music due to a distinct lack of oomph in the sub-bass. While this added to the crisp and organic sound, it was a little lacking when it came to music that needed impactful bass, such as pop or electronic music.

The Sennheiser HD 660S2 appears to be the German audio tech company's attempt to bring the charm of the first generation of the headphone to other genres of music. The improvement in the bass end is noticeable from the first listen: music immediately has more body in both the mid-bass and sub-bass ends, giving pop and hip-hop music the punch they need, as well as adding impact to OSTs and classical music. What's impressive about the 660S2 is that it adds the low-end while still producing the same amazing soundstage and instrument separation as the original 660S, without compromise.

The only downside to the HD 660S2 is that it loses some of the sparkle that the HD 660S had, although it's only a slight difference. The transparency that dropped my jaw while still there is less apparent. So ultimately, it's still a give-and-take game: do you want a headphone that sounds absolutely amazing while playing acoustic music, or do you want a headphone that is almost as good but can be used for many more genres of music? The great thing about both the HD 660S and 660S2 is their mid-range price, which means you can grab both pairs for less than $1,000 and get the best of both worlds.

Hands-on with Sennheiser HD 660S2
The HD 660S2 paired with the FiiO R7 Jeff Li/IBTimes US

Sound Source Pairing

Another difference between the two Sennheiser headphones that's not immediately apparent is the doubling of the impedance. The HD 660S has an impedance of 150 ohms, while the HD 660S2 has an impedance of 300 ohms. The increased impedance gives the HD 660S2 a less fatiguing high-frequency response when using a high gain setting, while still benefiting from the energy boost.

Based on past experience testing the Sennheiser HD 660S with various DAC/Amp sources, we found that the FiiO K9 Pro AKM edition was a sweet spot for opening up its superior holographic imaging, instrument separation, and naturalness. Pairing the HD 660S2 with the K9 Pro also produced excellent results, except for the aforementioned slight decrease in sparkle in the high range and the need for a slight boost in volume due to the higher impedance. However, it drives just as well as the 660S. What you're getting with the 660S2 is a boost in sub-bass that makes bass-heavy music much more enjoyable to listen to.

Hands-on with Sennheiser HD 660S2
A travel friendly package Jeff Li/IBTimes US

A Different Accessories Package

On the accessories front, it seems that the Sennheiser HD 660S2 is more geared towards portability compared to its predecessor. Instead of a hard box with custom molded foam inserts like the HD 660S, the new headphones come in a much smaller package and a more portable fabric carrying drawstring bag is included. The package also includes two cables: the 1/4-inch single-ended and the 4.4mm balanced jack, but the cable length has been shortened to a more manageable 1.8 meters (just shy of 6 feet) from the original 3-meter long cable.

Hands-on with Sennheiser HD 660S2
The Sennheiser HD 660S2 is arguably a more versatile version of the original 660S Jeff Li/IBTimes US

Final Verdict

Sennheiser, the German audio giant, is no stranger to dominating the mid-range open-back headphone market, and the HD 660S2 is yet another feather in their cap. As with each new release, Sennheiser manages to outdo themselves and improve upon the previous model. However, the HD 660S2 does come with a caveat: if you are a fan of the natural and organic presentation of acoustic instrument-based music that the HD660S excels in, then the original might be more suited to your tastes. However, for those seeking a sub-bass boost for genres such as electronic music, the HD 660S2 is the latest and greatest addition to the 600 series, and is sure to satisfy your audio needs.

Hands-on with Sennheiser HD 660S2

The Sennheiser HD 660S2 represents a remarkable evolution of Sennheiser's signature sound while retaining the hallmarks of its predecessor. The sub-bass boost and the more portable accessories make it a versatile choice that can handle a wider range of music genres. Audiophiles looking for a reliable, high-quality open-back over-ear headphone will appreciate the HD 660S2. As such, we're honored to bestow upon it the prestigious IBTimes Editor's Pick badge.