HD 660S

Sennheiser HD 660S Review – Modern Spin on a Classic

Sennheiser’s HD 600-series is legendary among audiophiles, known for its balanced sound and comfort. The HD 660S is the 2017 addition to this family, aiming to modernize that classic formula. After spending plenty of listening hours with the HD 660S, here are my candid thoughts on this recent edition to a legendary line.

Design & Build

The HD 660S sticks to the familiar 600-series look and feel, but with a sleek all-matte-black twist. It’s mostly plastic in construction, which might not scream luxury at first touch, but this design has stood the test of time – and there’s a practical upside: the plastic keeps it super lightweight and surprisingly durable. I’ve tossed around older Sennheisers in my day, and they just keep going (usually the only thing you’ll ever need to replace are the ear pads after heavy use). The headband has a metal reinforcement inside and the open-back grilles are metal, but everything else is high-quality plastic that doesn’t creak or flex in worrying ways. Overall fit and finish are on point: the HD 660S feels solid in hand and sits nicely on the head without weird rattles or loose parts.

A nice bonus in the box is Sennheiser’s inclusion of two detachable cables – one with a 1/4” (6.35mm) plug for your desktop amp, and one with a 4.4mm balanced Pentaconn plug. That balanced cable is a clear nod to the headphone enthusiasts who might want to pair the 660S with balanced-output gear. Both cables are a generous length (about 3m), which is great for home use, though they can be a bit unwieldy and very long if you’re right next to your source. No fancy travel case here – just a basic foam-lined storage box – but honestly, these are an at-home listening pair, so I don’t mind. In short, the HD 660S’s design is understated and functional. It might not turn heads like a flashy planar with wood cups, but it’s all about long-term comfort and reliability. Sennheiser knew not to mess too much with a good thing.

Comfort & Fit

Slip the HD 660S on, and one of the first things you notice is how light it is. At roughly 260 grams, it’s easy to forget you’re wearing them – until the clamp force reminds you. Yes, out of the box the squeeze is real. The classic Sennheiser clamp is here in full effect; it ensures a secure fit, but can feel like a vise on day one, especially if you have a larger head (or big ears that press against the pads’ inner foam). The good news: this is a fixable quirk. I gently bent the headband and after a day or two of “stretching” on a box, the HD 660S relaxed into a far more comfortable clamp. After that break-in period, I was able to wear these headphones for multi-hour sessions with no discomfort or hotspots.

The velour ear pads are plush and breathable, avoiding heat buildup and sweat – a big plus for long listening. They’re a snug oval shape, nicely soft on the skin. The ear cup openings could be a tad wider; my ears fit, but if yours stick out or are on the larger side, you might brush the drivers a bit. Still, the padding and lightweight build make the HD 660S a joy for extended use once the clamp is tamed. Even the headband has ample padding to distribute pressure. I’ve nodded off more than once with these on (blame the comfy fit and some very immersive music). Overall, Sennheiser nailed comfort, save for that initial out-of-the-box tightness. It’s the kind of headphone you can wear all day – truly couch-friendly cans – which suits their intended usage perfectly.

Sound Quality

Time to dive into the sound – and this is where the HD 660S shows its modern tweak on the Sennheiser house sound. In a nutshell, it’s a balanced, mid-focused headphone with a touch of extra energy up top, and a leaner bass than some might expect. It takes the warmly engaging soul of the old HD 650 and gives it a bit of a caffeine boost in clarity and speed.

Bass: The HD 660S’s bass is tight, fast, and well-controlled. Kick drums hit with a satisfying pop and bass guitars have texture, never devolving into muddiness. However, sub-bass lovers will notice the roll-off – below about 80Hz the party trickles out. In plain terms, the really deep rumbles (think cinematic sub-bass or the lowest synth drops) are subdued. Listening to electronic or hip-hop tracks, I found myself enjoying the punchy mid-bass but missing that last bit of deep-end grunt. For most rock, jazz, and acoustic music, the bass is perfectly adequate and actually very articulate – every note is distinct – just don’t expect head-rattling lows. The flip side is that this restraint down low means the mids and highs aren’t masked at all, contributing to the 660S’s clear, detailed character.

Mids: Ah, the mids – Sennheiser’s pride and joy. The HD 660S carries on the tradition with luscious, natural midrange reproduction. Vocals and guitars take center stage, rendered with a rich tonality that flatters voices and instruments alike. Male vocals have body, female vocals soar without harshness. There’s an intimacy here: vocals feel like they’re being sung just for you. Compared to its predecessors, the HD 660S’s midrange is a tad less warm and thick than the HD 650’s, but in exchange you get a bit more detail and immediacy. I found the midrange timbre to be spot-on – listening to acoustic tracks and classic rock, the realism in the vocals and midrange instruments gave me goosebumps. Importantly, the upper mids (around 3kHz) are nicely balanced; where older models could get a hint shouty or nasal in that region, the 660S smooths it out. This headphone was clearly tuned by someone who loves mids, and it shows.

Treble: The top end of the HD 660S is more pronounced than the older HD 600/650, bringing a welcome sparkle and clarity to the sound. This is the brightest of the 600-series bunch, though that’s still within a generally smooth, listener-friendly tuning. The treble delivers detail – cymbals have a nice crisp sheen and there’s a sense of air that the HD 650 sometimes lacked. That said, Sennheiser didn’t turn the HD 660S into a treble monster; it retains a touch of warmth. I did detect a slight peak in the lower treble (somewhere around 5-6kHz) that can make certain brighter recordings sound a bit aggressive or give a hint of grain. It’s minor, and many might not notice it unless listening critically or directly comparing to other headphones. By and large, the highs are smooth and fairly refined, with only the very uppermost frequencies (above 10kHz) tapering off gently. This means you won’t get the super airy, spacious treble of some planar magnetic rivals, but you also avoid harsh sibilance. In practical terms, the 660S’s treble gives music a lively energy and detail without crossing into fatigue territory for me.

Soundstage & Imaging: One area the HD 660S doesn’t particularly excel is soundstage width. The presentation is intimate – you’re seated close to the performers, rather than in a large hall. For some genres like small ensemble jazz or singer-songwriter stuff, this “up-close” sound can actually be engaging, placing you right in the mix. But if you crave a wide, speaker-like soundstage or holographic imaging, the 660S might feel a bit narrow. Lateral imaging (left-right separation) is fine and instrument separation is excellent (each layer in complex tracks is easy to pick out), but there’s not much sense of sound wrapping around you. As a result, I wouldn’t pick the 660S first for grand orchestral pieces or for gaming, where pinpoint spatial cues and width are desired. It’s not claustrophobic by any means – just a more cozy, in-your-head stage that’s typical of this Sennheiser series.

Dynamics: When it comes to dynamics, the HD 660S is punchier than its older siblings, but it won’t knock you out of your seat like some competitors. Macro-dynamics (the impact of big hits and crescendos) are decent – drums have a bit of slam – yet if you directly compare, a planar like the HiFiMAN Sundara can hit harder and feel more “alive” on dynamic swings. Micro-dynamics (the subtle variations and textures) are handled well; the 660S excels at conveying the nuances in vocals and instruments. It’s engaging, just not a bass cannon or a slam champion. Personally, I enjoy its balanced approach: it’s energetic enough to get my foot tapping, but also polite enough that I can listen for hours without fatigue.

Use Case Fit

So, who and what is the HD 660S best suited for? In my experience, these headphones are made for at-home listening in a quiet space. They are open-back after all – they leak sound out and let ambient noise in – so they’re not meant for commuting, office cubicles, or library use (unless you want to share your music with everyone around and hear every background noise). Settle into your favorite chair at home, hook the 660S to a good source, and it will reward you with a wonderfully immersive personal concert.

Genre-wise, the HD 660S shines with music that capitalizes on its sweet midrange and detail. They’re fantastic for classic rock, acoustic, folk, jazz, and classical. Vocals in particular come through beautifully, so singer-songwriter and vocal-centric tracks are a real highlight. If you listen to a lot of hip-hop, EDM, or big cinematic scores that rely on deep bass and expansive soundstage, you may find the 660S less satisfying out of the box. It’s not that they can’t play those genres (they’ll still sound clean and balanced), but you might miss the sub-bass rumble and wide presentation that other options provide. Of course, some EQ to boost the lows can help if you really want to stick with the Sennheiser sound.

For practical daily use, I find the HD 660S extremely comfortable for long work or study sessions (once the clamp is adjusted). They also work well for music production or editing thanks to their clear midrange and non-fatiguing balance – think of them as a semi-reference headphone you can actually enjoy music on too. As mentioned, they’re not my top pick for competitive gaming or movies if you want that enveloping surround effect, but for casual single-player gaming or Netflix in a quiet room, they deliver clear and natural sound. In short, the HD 660S fits the bill for a home-bound audiophile who values balanced, natural sound and comfort over flashier bells and whistles. If that’s you, these could become your daily drivers.

Amp & Source Pairing

One of the big updates with the HD 660S was a lower impedance (150 Ω) design, making it easier to drive than the classic 300-ohm HD 600/650. In theory, this means you don’t absolutely need a beefy amplifier to get good volume and sound out of them – and indeed, the 660S can run off modest devices better than its predecessors. I tested the HD 660S with everything from a laptop headphone jack and a portable dongle DAC, up to a dedicated desktop amp. Here’s the takeaway: they’ll make music with almost anything, but they scale noticeably with higher-quality amplification.

Straight out of my MacBook, for example, I was pleasantly surprised – the 660S sounded clean and detailed enough in a pinch. If it’s late at night and all you have is your laptop or a basic USB dongle, these headphones will still sing (the mids stayed rich and the treble lively, though the bass lost a bit of body). However, switching to a good amp/DAC combo was like giving them a shot of espresso. My JDS Labs Atom amp (an affordable but capable desktop amp) immediately tightened up the bass and opened the sound a bit. Moving further up to a more powerful amp, I heard incremental improvements: more authority in the bass, a touch more soundstage depth, and an overall smoother presentation.

The included balanced cable isn’t just for show either. Plugging the HD 660S into a balanced output (in my case, a balanced desktop amp) gave it a smidgen more headroom and dynamics – not a night-and-day difference, but perceptible in how the music had a bit more breathing room. If you have a high-end DAP or balanced amp, it’s worth using that cable.

In terms of synergy, the HD 660S is not overly picky but it does reflect your source’s character. Feed it a warm tube amp or a warm-sounding DAP, and it will mellow out a bit – bass gets a tad fuller and treble softens. Pair it with a very analytical amp, and you’ll get an ultra-clean, slightly leaner sound. I personally loved the 660S with a hybrid tube amp I own; the tubes added a pinch of warmth and romance, making the Sennheiser even more musical without losing detail. But even on a neutral solid-state amp, the HD 660S performs great. The key point is, while you can drive them from a phone or laptop, you’ll want a decent amp to hear them at their best – and luckily, that doesn’t have to break the bank. Even affordable amps like the Schiit Magni or JDS Atom will do the job. Unlike some planar magnetics or super high-impedance headphones, the 660S won’t punish you for using mid-tier gear, which makes them fairly versatile for various setups.

Value & Comparisons

At around $500 (often less these days), the Sennheiser HD 660S sits in the middle of the mid-fi headphone pack. It’s a competitive arena, with both longtime Sennheiser classics and planar upstarts vying for your wallet. How does the 660S stack up in value? And what about its closest relatives and rivals? Here’s a quick rundown:

• Sennheiser HD 650 (and HD 6XX): The HD 650 is the elder statesman that many enthusiasts know and love. It’s warmer, a bit more laid-back, and more “forgiving” than the HD 660S. The 650’s bass is a touch fuller in the mid-bass (though it also doesn’t hit deep sub-bass), and its treble is smoother and more rolled-off, giving it that famous “Sennheiser veil” to some ears. By contrast, the HD 660S sounds more lively and resolving – you’ll hear a bit more detail and clarity, especially in the treble, and the sound is faster and tighter. The 660S is like the HD 650 after a mild tuning overhaul: less veiled, more clarity, but consequently a little less of that romantic thickness. In terms of value, the HD 650 (or the Massdrop HD 6XX which is essentially the same headphone) can often be found for significantly cheaper than the 660S, which makes the 650 a fantastic bang-for-buck pick if you prefer its smoother sound. If you already own a HD 650 you’re happy with, the 660S isn’t a mandatory upgrade – it’s different more than it is unequivocally better. But if you wanted a bit more spark and speed while still staying in the Sennheiser family, the 660S delivers that. It’s a “best of both worlds” approach: blending some of the HD 600’s neutrality and HD 650’s musicality. New listeners deciding between the two should consider their taste: for relaxed warmth and cost savings, go 650; for a more modern, detailed take, the 660S is your guy.

• Sennheiser HD 660S2: Enter the sequel. The HD 660S2 (released a few years after the original 660S) addresses some of the complaints people had about the 660S – chiefly, the bass extension. The 660S2 reaches lower and hits harder down low, giving you the sub-bass presence that the 660S lacks. It also reverts to a 300-ohm impedance design, and in tuning it leans a bit closer to the classic HD 650 warmth, but with tweaks. In direct comparison, the HD 660S2 sounds fuller and warmer, with a more robust low-end punch, while the original 660S is leaner but a tad more airy up top. The soundstage and imaging remain similar (neither is very wide), though some listeners report the S2 has slightly better soundstage depth. The catch? The HD 660S2 is notably more expensive (it launched around $600) and it doesn’t make the original obsolete by any means. If you crave that extra bass and a smoother treble, and you don’t mind paying more, the 660S2 is arguably the better headphone overall – it feels like Sennheiser course-correcting to please the bass-needy fans. But the original 660S still holds its own in clarity and speed, and now you might find it at a discount. Value-wise, the HD 660S is a solid deal if you can snag it on sale, whereas the 660S2 asks a premium for those improvements. For many, the question will be: do you want to save some cash and possibly EQ the 660S, or spend extra to get that bass right out of the box? Either way, both are enjoyable listens, but the 660S2 is the one aimed at those who thought the 660S was a bit too anemic down low.

• HiFiMAN Sundara: The HiFiMAN Sundara is a planar magnetic rival that often gets brought up in the same conversations as the HD 660S – and for good reason. The Sundara (latest revision) comes in at a lower price (typically around $300–$350) and offers a different flavor. Sound-wise, the Sundara has a wider soundstage and more extended treble and bass. It digs deeper in the bass frequencies, so you’ll feel more rumble and weight in electronic and cinematic tracks. Its treble is also more elevated, giving a sense of air and sparkle that can make the HD 660S sound a touch dark or closed-in by comparison. Detail retrieval is one of the Sundara’s strong suits; it can resolve as much, if not more, detail than the 660S, especially in the highs. However, the midrange on the Sundara is a bit more recessed (and slightly cooler in tone) – voices aren’t as intimate or lush as on the Sennheiser. The HD 660S still holds the crown for midrange magic and natural timbre, whereas the Sundara can sometimes sound a bit clinical in the mids. In terms of comfort/build: the Sundara has a sturdy metal headband and yokes, and a more modern aesthetic, but it’s heavier on the head. Its clamp is gentler than the 660S (once the 660S is broken in), yet the Sundara’s lack of swivel in the ear cups can cause fit issues for some. Also, planar drivers like the Sundara usually need a bit more juice from an amp due to lower sensitivity – it’s not night-and-day, but the Sundara will benefit just as much from good amplification as the 660S, if not more. Value comparison: The Sundara offers tremendous value at its price – arguably outperforming the 660S in technical areas like soundstage and bass extension for less money. That said, build quality control has historically been a question with HiFiMAN, whereas Sennheiser has a long-standing reputation for reliability. At the end of the day, choosing between them comes down to taste: if you want a spacious, reference-like planar sound and don’t mind a hint of brightness, the Sundara is hard to beat for the price. But if you live for intimate vocals, a smooth midrange, and a slightly warmer tilt, the HD 660S still justifies itself – even at a higher price point – with a sound that many find more musical and emotionally engaging.

In the broader landscape, the HD 660S’s value proposition has improved now that it’s not the hot new thing – you can often find it at a discount, making it more competitive. It’s up against popular choices like the Beyerdynamic DT 1990 Pro (which offers a more V-shaped, analytical sound and much wider staging for about the same cost) or the Drop + Sennheiser HD 8XX (though that’s a different price league entirely). But sticking to its immediate peers, the HD 660S holds its ground by delivering that unique Sennheiser sonic recipe with a modern twist. It isn’t the runaway value champ (the Sundara probably claims that title in pure performance-per-dollar), but it isn’t overpriced either – especially for listeners who know they love the Sennheiser sound.

Conclusion & Verdict

The Sennheiser HD 660S is a successful modern remix of a classic, and I’ve grown genuinely fond of it. It takes the core of what made the HD 600/650 beloved – natural timbre, smooth yet detailed mids – and injects a bit of extra clarity and agility. In doing so, it sacrifices a little of that old-school warmth and doesn’t quite solve the 600-series’ age-old Achilles heel (sub-bass extension), but it still lands as a great all-arounder in the mid-fi headphone arena.

After weeks of testing, I found the HD 660S to be a headphone I can trust for just about any genre I throw at it, with a particular talent for rock and vocals that makes me reach for it again and again. It’s not a radical departure from its lineage – if you were hoping for a night-and-day revolution, the 660S might feel too familiar. And in absolute terms of performance, there are rivals that outshine it in specific areas. But the holistic experience of the HD 660S is undeniably enjoyable: it’s comfortable, built to last, and delivers music with a mix of precision and soul that few in its class manage.

Verdict: The HD 660S is a worthy addition to Sennheiser’s legendary lineup. It may not unseat the HD 650’s icon status, nor does it out-tech some planar competitors, but it strikes a lovable balance. Candidly, it’s the kind of headphone that might not blow your mind on first listen – instead, it wins you over track by track, hour by hour, with its honest, engaging sound. For audiophiles seeking a fast, thoughtful listen that stays true to the music, the HD 660S still hits a sweet spot. It’s a headphone I can easily recommend for those who want Sennheiser’s trademark mids with a bit more sparkle, and who understand that “better” in audio is often about synergy with personal taste. In my book, the HD 660S is a job well done – not perfect, but perfect for savoring the heart of your music collection. Enjoy the tunes!