Sennheiser HD 660 S Headphone Review

Sennheiser HD 660 S Pros&Cons

Sennheiser HD 660 S Specs

• Impedance: 150 Ω
• Frequency response: 10 – 41,000 Hz (-10 dB)
• Sensitivity: 104 dB/V @ 1kHz
• THD+N: < 0,04% (1 kHz, 100 dB)
• Weight: Approx. 260 g (without cable)

Packaging 

The first thing to notice about the outer packaging of the HD 660 S is that, apart from some text and images, it’s largely identical to that of rest of the HD-line. The mostly-black box and light-blue strip towards the bottom are unmistakably Sennheiser.

Removing the outer packaging reveals a secondary box, which serves as the main protective box for the headphones, and also double as a storage case. It’s all-black colour makes it rather unassuming as to what is on the inside.

Lifting the lid reveals the HD 660 S, 2 separate cables, a 1/4″-to-1/8″ adapter, as well as an instruction manual.

 

What’s in the box?

• HD 660 S
• 3m 1/4″ cable
• 3m 4.4mm Pentaconn TRRRS cable
• 1/4″-to-1/8″ adapter
• Instruction Manual

 

Accessories 

Well, not a great deal is included in terms of accessories. Whilst it’s nice of Sennheiser to release the device with 2 cables offering different terminations, the sheer length of the cables can be rather annoying. Seriously, 3m (10ft) is just way too much. Had it been coiled cables, then sure, that would be more convenient. As such, it seems the HD 660 S was aimed more towards studio use than for portable convenience, despite the fact that Sennheiser does specifically say that the HD 660 S is more portable friendly due to a lower impedance compared to its predecessors.

And speak of portability, the included 1/4″-to-1/8″ adapter is great, as the vast majority of portable devices (and perhaps even desktop devices) wouldn’t be able to accept the 1/4″ plug.

Read: Sony MDR1000x Noise cancelling headphones Review

Design

In terms of the overall design, the HD 660 S is very much in-line with the rest of the HD-series, in particular the HD 650 and HD 600. The overall form-factor seems largely unchanged, with the most obvious difference being the finishing and other cosmetic elements. Where the HD 600 had the strange paint-spatter finish (supposedly to mimic marble), the HD 650, on the other hand, had a far more subdued and glassy metallic-grey finish. For the HD 660 S, they’ve refined and simplified things even further.
Personally, I’m not a fan of glossy plastic finishes, as they just somehow tend to make the product look “cheaper” to me (especially if they attempt to create a mirror-finish). As such, the matte-finish of the HD 660 S is far more appalling to me.
Unfortunately, Sennheiser has stuck with a construction that is almost exclusively made out of plastic. This is the same type of construction that they’ve been using for about the last 20 years at least. The only metal parts seem to be with the drivers, the metal parts that slides in and out of the headband, and perhaps the grills.

As far as the quality of construction is concerned – well, the plastic used certainly doesn’t feel cheap per se, but the HD 660 S certainly doesn’t feel like a premium product when compared to something like the Hifiman Sundara either. In fact, if I remember correctly, the Audio-Technica M40X that I owned a few years back seemed to have a bit more of “solid” feeling(or at least on par with the HD 660 S).

Compared to the HD 650, the HD 660 S does feel a little more sturdy, but that might also be due to the fact that the demo HD 650 that Sennheiser sent me has been used more and so has a bit more wear.

Generally the HD 660 S feels like a reasonably comfortable set of cans, but they did require some break-in. Out of the box, clamping force is quite high, so I just extended the headband adjustment out a bit, and then placed the headphones on my studio monitors to stretch it out a bit. Getting them to that “perfect” amount of clamping force (for me personally) would require a bit more time than what I’ve been given to review the cans, but the few days that I left them on the speaker helped a great deal.
The lightweight-nature of the HD 660 S also certainly helps in the comfort department, as does the relatively soft padding on the headband. The padding isn’t anywhere near as nice as what you’d get on something like the Bose QC35 II, for example, but I also have experienced way worse padding in the past.

One aspect of the design that I simply cannot wrap my head around is the fact that the headband adjustment system doesn’t seem to have any markings. As such, you really have to first adjust one side (and count how many “clicks” of adjustment are being done), and then repeat for the other side. It’s exactly the same on the HD 650. So really, in at least 15 years, Sennheiser kept forgetting or couldn’t be bothered to change this? Adding a bit of paint or engraving some reference markings can’t be that difficult, can it?

Lastly we get to the actual drivers. Now, Sennheiser claims that the drivers used in the HD 660 S are based on the drivers used in the HD 700. However, various measurements online of the impedance curve suggest that they might in fact be the same drivers after all. But, to confuse matters even more, if we just look at and compare what the HD 660 S drivers look like when we removing the earpads and dampening foam, then things look identical to the HD 650. It’s only when we look at the drivers from behind (through the grills) that we see some differences.

Overall, in terms of the design of the HD 660 S, Sennheiser seem to have pretty much gone with an “if it ain’t broke, don’t fix it” approach. Which is a bit of a pity, as there are a few aspect which certainly could’ve used some improvement.

Sennheiser have also touted the HD 660 S as being more “portable friendly”, due to an impedance figure that’s half of that of the HD 650 and HD 600.
However, a more important figure to look at is perhaps the sensitivity, as the sensitivity of the HD 660 S is only slightly higher than that of the HD 650. What this means is that, irrespective of the greatly reduced impedance figure, the HD 660 S honestly isn’t that much more power-efficient than the HD 650.

Sound

Test Setup
Source: Shanling M2s, PC
DAC/Amp: Melokin DA9.1, IFI Micro iDSD Black Label

Sennheiser’s HD-line is actually rather legendary, so much so that it’s even got somewhat of a cult-following. In fact, many use and regard (for quite some time now) the sound characteristic(s) of the HD 650 and HD 600 as the baseline for what should be considered to be a damn good sounding set of open-backs.
Whilst both models do have their own strengths and weaknesses, their sonic differences mainly seem to come down to a person’s preference. Where the HD 600 sticks perhaps closer to an objectively “neutral” signature, the HD 650 has, in comparison, more emphasis in the bass region along with an overall warmer and smoother character.
However, what both of them lack (almost entirely) is sub-bass extension. The HD 650 definitely fares somewhat better in this regard, but neither come close to what you could expect from a set of modern open-back headphones equipped with planar-magnetic drivers.

So, where does this leave the newest edition to the family? Well, for starters, I have unfortunately never had the opportunity to demo the HD 600, and so when trying to compare it to the rest of the HD-line, I’m entirely relying on my interpretation of measurements found online as well as the impressions of other users and reviewers (so use these comparisons as somewhat of a reference, but not as gospel). Thankfully Sennheiser did send the HD 650 along for me to be able to make a more direct comparison.

Broadly speaking, the HD 660 S seems to perform similarly to both the HD 600 and the HD 650. Perhaps the biggest drawback of all 3 models, as mentioned, is a lack of presence in the sub-bass region. So, if you were hoping that the HD 660 S would cure that inherent lack of bass extension, this aspect will be rather disappointing to you.
It should be noted, though, that this “flaw” is very much dependent on the type of music you listen to. If your preference is for music that doesn’t have much energy in the sub-bass region, then this will likely not be an issue for you. It’s not that the sub-bass “isn’t there”, but rather that it’s just significantly lower in volume relative to the midrange.
Whilst comparing the 2 I actually noticed how much their sound improved (subjectively) when I flipped on the XBass+ switch on my Micro iDSD BL. Suddenly both models just “came alive”, as though finally all that the music has to offer is being pushed through. There were certain tracks that I were listening to which, after flipping the switch, I found myself saying “oh right, there’s the bass guitar”. But again, this will depend on your choice of music. More natural instruments (and vocals) generally don’t tend to have much energy in the sub-bass region, whereas more modern music that often rely somewhat heavily on artificial bass and sub-bass notes and other generated sounds do come across a bit “thin” on the HD 650 and HD 660 S without the aid of a bass boost.
Moving on to the bass region, the HD 660 S portrays these notes with more “punch”, whereas the HD 650 has a more fluid and deeper apparent rumble (a difference which is more noticeable with a bass boost).
But really, the midrange is where the HD-line have always shined. I truly do understand the affection people have for the midrange of these headphones and why they consider it to be a baseline.
It’s in comparing the midrange and treble of the HD 660 S to that of the HD 650 that I hear more distinct differences in their characteristics.
Yes, the HD 650 does have that “Sennheiser-veil” going on, but this could be regarded as sounding “effortless” and non-fatiguing. This could be a positive or a drawback depending on personal tastes.
When listening to the HD 660 S and switching back and forth with the HD 650, the HD 660 S doesn’t seem to have that same veil, and perhaps as a result of that specifically it also portrays the music with a more forward presence. It’s a more upfront midrange, which I know many people prefer by quite a large margin.
You get some headphones that are just too warm and too smooth, so much so that they end up masking some details in the mids and highs, and the HD 650 does seem to fall slightly into that camp, at least when compared to the HD 660 S. The details are there, but they don’t quite have the same presence as they do on the HD 660 S.
But, that’s not to suggest that the HD 660 S portrays them in such a manner that it feels like they’re hammering away at my ears as if to scream “I’m here, I’m here…notice me!”. The HD 650’s mids and highs are just softer and more relaxed by comparison.

But that does beg the question – is the more apparent “clarity” offered by the HD 660 S as a result of an objectively more accurate reproduction of the sound, or simply a different flavour? Honestly speaking, your guess is as good as mine, but what I could say is that, if you like the HD 650, but want more presence in the mids, then the HD 660 S could very well be a good sonic upgrade for you. But, if you like the HD 650 just the way it is, then I’d still suggest that you try the HD 660 S out and then decide for yourself which one suits you better.

 

Read: Sennheiser PXC 550 Wireless Headphones Review

Value 

Judging the relative value of the HD 660 S proves to be a rather difficult task. On the one hand I want to respect the heritage of the HD-line, but on the other hand I also need to take into account the competition. Whilst I certainly do appreciate what seems to be a marginal step up in build quality and a refinement in design and finishing compared to the older models, it’s in the bang-for-buck performance compared to more modern technology used in modern-designed headphones that really makes me wonder about the HD 660 S.
You see, the thing is, The HD 600 and 650 were released roughly 21 and 15 years ago respectively. And, to be rather frank, it also feels that way.
In some regard the HD 660 S simply feels like a marginally more modern interpretation of a roughly two-decade-old classic.
Where I feel most uncertain, though, is with regards to the price. Both the HD 600 and 650 had a price tag of around $500 when they were released. So, do we commend Sennheiser for being able to offer the new model at a price that seems to have avoided any and all forms of inflation, or do we consider what the competition has to offer for the same cash and judge the value based purely on that?
Perhaps if the price was dropped to a more reasonable $300, then things would make more sense. But, as things stand currently, the overall value of the HD 660 S is simply lacking.
If we take into account what the HD 660 S offers compared to what the likes of the HifiMan Sundara (same price-tag) or more modern (yet cheaper) products from other competitive brands offer, then the HD 660 S really doesn’t seem to pack as much relative value. Is the HD 660 S good? Yeah, it is a good set of cans, but there better built and arguably better sounding headphones out there for the same price. Personally, I do still prefer the more laid-back nature of the HD 650, but I wouldn’t necessarily consider either the HD 660 S or the HD 650 as a “go-to” headphone for my personal tastes. If the 650 had just a little more sparkle, then I might very well consider it.

Rating

The TECH MERIT rating system is designed to take as many aspects of the device into account as possible. As such, we have a basic rating, as well as a final rating. The basic rating rates the product purely as a high quality portable audio device, and is generally a good indicator of how it stacks up to its rivals in terms of standard features and specs. The final rating, however, grants bonus points for any extra features and specs that aren’t quite as common, and is a great way to judge the product as a complete package.

 

Build
Total: 8.1

Sound
Total: 9.3

Portability
Total: 8.6

Extras
8.2

Value
Total: 8.6

 

Final Rating: 8.6

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