Sennheiser HD 660 S Dynamic Headphones

Way back in 2003 (Way back considering the timeline of headphones) I first heard a pair of Sennheiser HD650’s. They were the new flagship cans from Germany and they redefined for me what quality personal audio sound was all about. Over the years I have used them with many amplifiers; Solid State, Tube, and Hybrid all sounded terrific with these amazing headphones. A few years later the HD800’s arrived, and they were a big leap forward in sound stage and detail, however, while I enjoyed my new reference HD800’s I still came back and listened to the HD650’s. Now, augmented with the Toxic Cables Silver Poison cables, they had become a favorite old pair of shoes; always comfortable.

Today we have the Sennheiser HD 660 S headphones and their goal is to move the vaunted HD 6xx line forward. Coming in at the same retail price as the HD 650 of $499 USD, the HD660’s have a lower impedance at 150 Ohms vs the HD650’s 300 Ohms, making them more portable audio friendly. Connectivity is enhanced too by the choice of cables and adapters provided in the package. The standard ¼” TRS jack is on the primary cable. A 1/4” to 1/8” adapter is provided to connect to a DAP stereo plug and there is another full cable terminating in a four-ring balanced connector (a 4.4mm Pentaconn TRRRS balanced plug) for higher end DAP’s and Portable amplifiers that offer balanced output. The headphone connection on the cable is the same as the HD650’s making cable updates easy. One nit to pick is for a headphone touted as more portable friendly, both cables are 10 feet long. It would have been nice to offer say a 4 ft (1.2M) option while out and about.

The driver has been updated to a new stainless-steel fabric that is touted to improve the speed and transparency of the music. It is apparently based on the HD700’s driver re-engineered to fit into the HD 6xx form. A new striking matte black and anthracite color give them an updated and modern look. One thing that has not changed much is the very comfortable ear pads and headphone padding. I appreciate the fact that all pads are replaceable should they wear over time. I have always enjoyed my long listening sessions with the HD650’s and the HD660 S’s goal is to continue that tradition.

Listening to the HD 660 S’s on my reference Simaudio Moon 430HA headphone amplifier, I found a definite increase in treble energy vs the HD650’s. This is definitely a brighter headphone while still retaining the basic family sound. Both headphones are rated to 41,000 Hz but there was a more strident upper end to the HD 660 S. Indeed, I found the there was an edge of grain to the HD 660 S that I was not experiencing on the HD650’s. On Fleetwood Mac’s “The Chain” (1977 Warner Bros. 24/192), the steel guitar during the intro has a jangling quality to the sound of the strings. The HD650’s managed this passage in a natural way. The strings rasping against the guitar neck sounded real. The HD 660 S’s had a slightly coarser sound adding an edge that was less refined. As the song progressed I did appreciate the mid-range of the HD660 S’s as the HD650’s offered up the more veiled presentation the HD650 is known for. I wished there was greater clarity to the HD 660 S to better showcase that increased transparency.

Shifting to Christina Aguilera’s Stripped album (2002 RCA 16/44) “Walk Away” is a modern torch song featuring Christina’s incredible vocals. The presentation with the HD650’s is a bit soft but incredibly smooth. The veil that occupies that 800-1500 Hz range is in evidence, however, it is not distracting. The HD 660 S definitely breaks through this area and offers a brighter presentation. I found myself considering the trade-off between the veil and the loss of purity with the grain. Female vocals of Ms. Aguilera’s caliber cry out for optimal transmission purity and so while I still enjoyed the song there were considerations with each presentation. I had let the HD 600 S’s break-in for about seventy-five hours, perhaps they needed more time for the new driver materials to completely come into their best form?

A few days and more break-in time later I selected a favorite version of Beethoven’s “Moonlight Sonata” by Benjamin Zander (1999 16/44). This piano work is one of my favorite versions if this classic. The HD 650 had good pace and flow and by now I was trying to not be as cognizant of the veil. Still, I very much enjoyed the smoothness of the presentation. Moving to the HD 660 S The piano had a more vibrant timbre allowing more of the shine of the notes to come through. It seemed a bit more break-in was useful for these headphones. There was still a hint of the original grain, but I suspect that will dissipate more with additional time. There was a level of brightness that the HD 650 could not match but the family sound signature was certainly in evidence. A good thing too as the HD 650 still is a highly listenable headphone.

Wrapping up the listening I went from a classical masterpiece to a rock three-chord masterpiece. “Fool for the City” from Foghat’s same-titled album (24/192 HD Tracks) has been a great tune for over forty years. Here listening to the twin guitars and pounding bass and drum line I preferred the HD 660 S. The additional brightness gave more life to this 70’s radio staple. The additional energy it conveyed made the presentation more immersive and engaging. I listened to most of the album and simply enjoyed some great classic rock. Good times.

If it seems like I have been tough on the HD 660 S, I have been. When a new headphone purports to replace a true classic it better deliver, or what was the point? In this case, it is a mixed bag. I suspect it will boil down to individual preference more so than usual. Clearly, the heritage of the HD 6xx family is there. However, there are definitely two flavors to choose from. Do you want the more laid back smooth HD650 or the brighter and possibly more revealing HD 660 S? They are both excellent headphones and considering the nose bleed pricing for today’s flagships these are both able to deliver a nice presentation for a fraction of the market is asking. If you have a friend with the HD 650’s go listen to them, then find a store carrying the HD 660 S and spend some time with them as well. If you are near a meet get there and find them. You may be able to audition them together. Either way, you go it will be fun deciding.

Technical Specifications:

Impedance: 150 Ohms
Connector: 6.35mm / 4.4mm Pentaconn
Frequency Response: 10 – 41,000 Hz (-10 dB)
Sound Pressure Level: 104dB at 1V 1kHz
Ear Coupling: Over-Ear Circumaural
THD + N: less than 0.04% (1 kHz, 100dB)
Transducer principle: Dynamic, open
Weight w/o cable: Approx. 260g
Price: $499 USD

Associated Equipment:

Simaudio Moon 430HAD Solid State amplifier/DAC
ALO Audio Studio Six SET Tube headphone amplifier
Pass Labs HPA-1 Amplifier
PS Audio DirectStream DSD DAC w/ Red Cloud firmware
PS Audio DirectMemory Player
Aurender A10 Streamer/Player
Sennheiser HD650 Headphones
Sennheiser HD800 Headphones
Toxic Cables Silver Poison cables

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Eric Neff

A 30+ year Audio veteran, I sold high-end two-channel in college and defected to Multi-channel for many years only to be pulled back in to two-channel once more. Tubes are a favorite. I run Cary gear. I am a Sennheiser and Apple fan-boy. I switch between Vinyl and digital. If it sounds good, it is, and the chain is the thing.


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