Sennheiser HD 660 S Headphones

• Review Summary
• Review Specs

Pros	Good detail, solid soundstage, and clean neutral sound. Ideal for jazz and orchestral music lovers.
Cons	No carrying case, no shorter mini-plug cable. A little shy on the bass and midrange richness.
Summary	High-quality, neutral headphone with clean approachable sound quality. Pairs well with a portable headphone amp, but will work fine directly from a phone. Enjoy high-end audiophile performance at affordable price.
Value
Performance
Overall

Manufacturer	Sennheiser
Model	HD 660 S
Headphone Type	Open Back
Sensitivity	104dB/V @ 1mW
Nominal Impedance	150 Ohm
Review Date	January 17, 2018
Price	$499.95

The Sennheiser HD 660 S replaces the highly regarded HD 650 and brings with it a new, more efficient driver design. The new design cuts the impedance in half, making the HD 660 S an easier headphone for mobile devices to power. This line of headphones is legendary for bringing high quality, accurate music reproduction at an affordable price. In fact, the Sennheiser HD 580 was my first quality headphone and gave me my first taste of the audiophile world. The new HD 660 S continues that tradition of beautiful, accurate sound and should be considered when shopping for a new pair of headphones but isn’t without its flaws.

Upon first inspection, the Sennheiser HD 660 S is a handsome pair of headphones with nearly the same design as the HD 650. They retain the signature Sennheiser oval shape and single, padded head strap. Unlike the glossy dark grey finish on the HD 650, the HD660 S is a matte black. It’s a good looking headphone, classy and not flashy. Supplied are two lengthy cables, one with a 6.3mm (¼”) plug and the other with a Pentaconn balanced 4.4mm (this is NOT a mini-plug and will not work in common headphone jacks!). Also supplied is a ¼” to 3.5mm adaptor for use with most portable sources. At 260 grams, these headphones are fairly light, roughly the weight of 2 bananas. If you are planning on taking this on the go, be prepared for some cable and dongle management. It’s not pretty…

Hooking up to an iPhone requires the long 9’ cable with the ¼” to mini-plug adaptor and then a lightning adaptor. It ends up being a lot to manage. At 150 ohm down from 300, these new cans feature a lower impedance than the HD 650 they replace. This means they should be easier to drive on your portable device.

Straight out of the box the HD 660 felt pretty tight on my head. I was able to adjust them a tad to alleviate some of the clamping pressure and after a couple weeks of usage, I found the Sennheiser HD 660 S to be pretty comfortable.

That’s all well and good but how do they sound??

For most of my listening, I used an iPhone 7 Plus connected to an Oppo HA-2 portable headphone amp. The low gain setting on Oppo HA-2 offers plenty of output with the Sennheiser HD 660 S. I also connected straight to the iPhone via Apple’s stupid but courageous 3.5mm to lightning dongle.

The Sennheiser HD 660 S continue the company’s trend for accurate and musical reproduction. Their sound is neutral and detailed, but still warm and approachable. I wish I had the 600 or 650’s to compare directly to, but I was only able to compare to two of my favorite cans in that price range, then Hifiman HE-560 and Oppo PM-3.

I like the Sennheiser HD 660 S, they are a good sounding headphone, but the Oppo PM-3 is impossible for me to give up. The two planar magnetic cans (Hifiman and Oppo) deliver better low-frequency response and a warmer, more dynamic sound. Passages where I expect a vocal or instrument to pop out with increased dynamics tended to lay a little flat on the HD 660 S.

If you intend to drive headphones directly off a phone, that takes the Hifiman out of the running. They are fantastic sounding headphones, but require a portable amp and will sound even better from a desktop amp with more headroom. Both the Oppo and Sennheiser performed fine via my iPhone 7 Plus, but the Oppo PM-3 was able to deliver a louder and more dynamic sound. 2-3 notches from max volume was about right for most music types. Maxed out the iPhone just can’t push the Sennheiser’s to what they are capable, so I would still recommend a good portable amp for optimal sound.

Norah Jones

As soon as Norah starts singing on “Don’t Know Why”, I immediately noticed how firmly planted the image of her voice was within the soundstage. She sounds great on the HD 660  with excellent tone and detail on every piano note, loud and soft. The upright bass is clean and consistent, though lacking a bit of body. On “Shoot The Moon” the soundstage is wide, although not exceptionally deep. I find the Sennheiser HD 660 S present all the artists on jazz recordings with ease, with a natural sound which is free of any coloration. The artist’s presence on stage is solid and planted, but not as three dimensional as the planar magnetic cans.

Kanye / Drake

If you listen to a lot of hip-hop and rap, I’ll be honest, the Sennheiser HD 660 S is not the best tool for the job. Although you can listen comfortably at higher volume levels with low distortion, there isn’t enough bass response for this genre. Kanye’s “Dark Fantasy” sounds great, but I wish the bottom octaves were kicked up a notch. My opinion is that most listeners of this genre with feel there’s not enough bass. “Runaway” is well articulated and the more I listened the more I enjoyed the HD 660 S presentation, which I’d describe as detailed, natural and non-fatiguing. Although detailed, the HD 660 S did not tend to reveal harsh poor recordings often.

Radiohead

Immediately the HD 660 S presented me with a warm rich guitar riff of the opening of “Airbag.” I noticed good pop to the drums, thanks to the quick response of the HD 660 S’s dynamic driver design. On “Exit Music” Thom’s voice has a big intimate sound but isn’t overly in your face, murky, or overbearing. The accompanying guitar has a nice tangibility to the strumming. Overall this track sounds great on the HD 660 S.

When the bass line enters on “Melatonin” it pulls the vocals and synths together, completing the build-up of the song, but the HD 660 S is just a little too shy with that. On the other hand, the bass throughout A Moon Shaped Pool, particularly “Identikit”, is deep and strong enough to carry everything going on in the Radiohead spectrum without overwhelming vocals and other details. The HD 660 S is no slouch in the detail department, in fact, that’s where they shine. I hear more to the guitar strings vibrating, the piano keys knockin around, and percussion keeping the beat.

Orchestral Music

Jóhann Jóhannsson’s “Flight From The City” is made up primarily piano, strings, and synth. The track has a full body and lovely warm tone on the HD 660 S. Piano is a fairly common instrument in the music I listen to most, and without fail, every piano recording sounded pleasant, natural and focused. Strings were wispy and clean sounding, never coming off too metallic or murky.

Jazz

“Blue in Green” from Miles Davis has wonderful ambiance, puts you right at the club. The sax solo via the HD 660 S is laid back, presented farther from you. It’s a clean sounding performance which I appreciate, but my preference is the more direct, dynamic delivery of the Oppo PM-3. I feel more passion coming through, but if you want to hear more of the breath of the sax and click of the keys, the Sennheiser’s are a better choice.

HD 660 S Competition and Conclusions

The Sennheiser HD 660 S features accurate, quick response with excellent detail, but limited bass output. The midrange is warm and clean, but lacking some richness. Both the Oppo PM-3 and Hifiman HE-560 have better midrange and a more three dimensional sound, the HE-560’s having the best soundstage of the bunch. Where the Hifiman loses is in its portability. They are the hardest to drive, but also sound the best when being driven by a high-end desktop amp. In terms of portability, the Oppo PM-3 wins hands down. The lack of a shorter cable terminated with a mini-plug hurts the Sennheiser’s portability and its open back design does not lend itself to a noisy open office space. Still, even with these complaints, I enjoyed my time with the new HD 660 S. They are a very good sounding headphone that does a lot of things well. If these were my first pair of high-end headphones like the old 580’s were, I’d be instantly pulled into this crazy audiophile addiction.