Posted on 21st May, 2018


It's hard to believe, but Sennheiser's HD 600 were first released in 1997. They've now been manufacturing and selling this model headphone for over twenty years! Sennheiser, after all these years, has finally released a new headphone to the legendary HD 600/HD650 family: The HD 660 S. Just like it says on the box - The Legend Continues!


HD 660 S

Over-ear headphones

$799.95 RRP

It's hard to believe, but Sennheiser's HD 600 were first released in 1997. They've now been manufacturing and selling this model headphone for over twenty years!

The slightly younger sibling to the HD 600 is the HD 650, released in 2003.

These two headphones have been the juggernauts of mid-level headphones this entire time, and they still sell like hotcakes. Which is why I was so surprised when I heard the rumours that were was a new model being released to the HD 600/650 line. Contacting Sennheiser to confirm if the rumours were true, the press release was promptly received confirming the news.

Sennheiser, after all these years, has finally released a new headphone to the legendary HD 600/HD650 family: The HD 660 S. Just like it says on the box - The Legend Continues!

Could this new release possibly live up to its famous sibling’s heritage?


When Sennheiser headphones bear the “S” moniker, it means a few things: Sexy matte black styling, sleek contoured lines, minimal and clever branding, and incredible build quality.

The HD 660 S has all these qualities in spades. The HD 660 S is shaped almost exactly like the HD 600 and HD 650, but with slightly thicker pads, and some upgraded padding on the headband.

The oval-shaped, open-backed cups are designed to follow the shape of the human ear and feel like they are sturdy enough to survive a short drop.

The HD 660 S comes bundled with heaps of goodies in the box:

  • 3m cable with Pentaconn connector (balanced)
  • 3m cable with 6.35mm connector (unbalanced)
  • 6.35mm to 3.5mm adapter

This is the first time I’ve ever seen a headphone come with a 6.35 to 3.5mm connector - hats off to Sennheiser on that one.

Weighing in at 260 grams, the HD 660 S is lighter than the 330-gram HD 800, and the same weight as its older HD 600 and HD 650 siblings.

Inside the headphone

Before the announcement of these headphones, rumours were running wild that Sennhesier had used the same driver as the HD 700. However, Sennheiser has since stated that it's an entirely new driver made exclusively for this release. It is possible, however, that this new driver was based on the old HD 700 driver, as they both share the same size and impedance.

This impedance difference is interesting to note, because the HD 600 and HD 650 both shared the same 300-ohm impedance, whereas this new model has taken a drastic turn in halving that number to 150 ohms.

Sennheiser say that the choice for the lower impedance was for the right reasons:

Offering a lower impedance of 150 ohms, the HD 660 S can be enjoyed with HiRes mobile players or when directly connected to high-quality, stationary HiFi components.

These drivers are constructed with a precision stainless steel fabric, which apparently helps to control the diaphragm movements during playback. The voice coils are lightweight aluminium, and each pair of drivers are matched together with less than 1db of variance.

Using the headphone

As is typical with the HD 6XX series, the clamp is initially quite strong. However, the larger (and softer) pads make it a more comfortable experience this time around. Over time, the headband should loosen up slightly, and the clamp will become less firm.

Despite this clamp, the HD 660 S are still quite comfortable and are firmly held onto the head.

Sennheiser claimed that the lower impedance of these headphones would enable playback on a wider variety of sources, and this seems to be the case. Using portable amplifiers or even a mobile phone, rendered impressive results with the HD 660 S.

Initial testing with a Galaxy Note 8 smartphone even managed to drive these to louder-than-comfortable volumes, which is impressive.

The HD 660 S also performed admirably out of an OTL tube amp, despite the mismatch in output impedance. Using OTL amplification was always my favourite matching for the older HD 600, and I’m glad to report the combo still works well with this new iteration.

During testing, the best matching I found was with the Chord Electronics Mojo. Using the 6.35 to 3.5mm adapter and the Mojo on low-gain mode, the real magic of the HD 660 S was unleashed. The Mojo didn’t feel like it was struggling at all, and there were plenty of volume steps to play with, allowing for minor adjustments to be made.


The HD 660 S has clean and detailed bass, which doesn’t feel like it ever wants to reach out of the ear cups and beat you over the head. There is a decent amount of tightly driven punch, but nothing earth-shattering. Just smooth, clean midbass kicks, a light rumble for subbass, and no muddy bleeding into the lower mids.

The midrange is quite forward, and paves the way to a very clean and revealing listening experience, especially when it comes to vocals and acoustic tracks. These types of tracks can be particularly engaging as a result. Because of this forward signature, some songs can be a little shouty or too bright. However, I was able to easily tame this with the OTL tube amp, or the right source gear.

Cueing up I Think So by Rival Consoles, there is a abundance of detail and nuance in this track and listening to it with a well-resolving headphone can be staggering. The samples in this song begin with such a low level of volume, and creep louder and louder, reaching an eventual crazy crescendo. When listening to it with the HD 660 S, you can hear the samples coming from a mile away, even when they gently fade in.

The imaging ability of these headphones is excellent.

A good example of this can be heard when listening to God’s Away On Business by Tom Waits. The raspy and harsh vocals are forward in the mix, and every instrument played in the track can be individually picked out and listened to. Even the smaller pieces, panned all the way to the edge of the mix, can be easily identified, and the subtle timbre of the instruments is easily audible.

As these are open-backed headphones, you would never expect these to isolate that well. However, these are really 'open' headphones. Due to the oval-shaped ear cups, there is a lot more open surface area compared to a typical open-backed headphone. This means that while they won’t isolate at all, they will breathe beautifully over longer listening sessions.

Compared to HD 800 S

While it might sound bizarre to compare two headphones from completely different price brackets, trust me on this. They are from the same family, both bear the “S” moniker and are both reworked versions of headphones with legendary status.

While the HD 660 S doesn’t quite have the same bass depth and reach as the HD 800 S, there is more punch and vibrancy to the midbass. The HD 800 S feels a little more gentle and laid-back, with a more forgiving upper-midrange. The HD 660 S, in comparison, feels much more forward with the vocal range, but with less clarity, and a smaller soundstage. The HD 660 S is easier to drive and doesn’t require as much power from a source device.


Sennheiser has seemingly opened the bonnet of the gentle HD600/650 headphone, and have strapped a supercharger to the engine inside.

I’m happy to call the HD660S the “younger sibling” to the HD800S. They are indeed cut from the same cloth, in many respects.

Some die-hard fans of the HD600/650 may not appreciate the more forward sound signature, but others will get a huge kick from the newly invigorated bass levels, and upper-mid reworking.

For more information visit Sennheiser.


  • Impedance - 150 Ω
  • Connector - 6.35 mm / 4.4 mm Pentaconn
  • Frequency response - 10 – 41,000 Hz (-10 dB)
  • Sound pressure level (SPL) - 104 dB at 1V 1kHz
  • Ear coupling - Over-ear (circumaural)
  • THD + N, total harmonic distortion and noise - < 0,04% (1 kHz, 100 dB)
  • Transducer principle (headphones) - Dynamic, open
  • Weight w/o cable - Approx. 260 g (without cable)


    Matthew Jens's avatar

    Matthew Jens

    Constantly keeping himself busy, Matthew is a production manager, Brazilian jiu-jitsu blue belt, Head-Fi fanatic, coffee enthusiast and all-round cool Dad.

    Posted in:Headphones
    Tags: sennheiser 

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