Review written by Ian Dunmore (@Torq)

Introduction

The Sennheiser HD820 is a closed-back, dynamic, flagship headphone and the latest entrant in the German company’s HD8XX series - which first saw life in 2009. Both prior models, the highly regarded HD800 and HD800S, are open back designs and both remain in Sennheiser’s lineup.

The pair of HD820 I’m reviewing here are my own pair. As with the HD800S before them, I had them pre-ordered well before they were actually shipping. Oddly, both models were bought from headphones.com (I’ve been a customer since buying a HeadRoom Supreme, from then-CEO Tyll Hertsens himself, back in 1996). Headphones.com not only had the best price but also the earliest apparent availability - which they delivered on as promised.

Technology

Like their predecessors, the HD820 features Sennheiser’s unique “ring radiator” driver technology, with 300 ohm nominal impedance and similar 103 dB SPL sensitivity.  Only now they are coupled with a highly-visible, glass, acoustic reflector/lens that is intended to dissipate and re-direct the back-wave from the driver into a series of acoustic absorbers that line the perimeter of the ear-cup behind the driver.

This is a stark technological contrast to more traditional closed-back headphone designs, including models from Sennheiser, that have relied on simple damping materials, typically various foam and fabric layers, to absorb the energy emitted from the back of the driver. This is done so that it doesn’t bounce back from the driver cup and interfere with the primary wavefront from the front of the driver. Even so, closed back headphones often sound muddier, thicker and more closed-in than open-back designs that do not have to deal with this back-wave reflection.

Has Sennheiser’s unique approach to controlling this reflected acoustic energy been successful in preserving a more open and transparent performance? That will, of course, be the focus of the “Sound” section of this review.

Review Equipment & Material

Sources and amps used in this review include the Chord DAVE, Chord Hugo 2, Schiit Yggdrasil, Woo Audio WA234 Mk2 MONO, SPL Phonitor x and iFi Pro iCAN. Headphones used, for comparison, include the Sennheiser HD800/HD800S, Focal Utopia open-backs and Sony MDR-Z1R, Fostex TH900 Mk2 and ZMF Eikon (Padauk) closed-back models.

The majority of the music I use in my evaluations is in “Red Book” CD format (16 bit, 44.1 kHz), most of which comes from CD rips; an initial playlist for my audition listening can be found here. Where appropriate/referenced, I utilize a number of high-quality, high-resolution, albums, needle-drops, and also some native DSD content.

Build

Superficially the HD820 looks to have the same fundamental build as its other 800-series stablemates. Indeed the adjustable, padded, microfiber-clad headband appears to be identical to the that on the H800S, right down to the embossed model and serial number on the top.

From the thicker yokes on down, however, while hard to see in pictures, the differences become apparent. In place of open silver mesh backing you have ridged, black, solid panels. The cup surround is flatter and doesn’t curve into the cup area. And, of course, the backs of the drivers are sealed with prominent, concave, glass discs - which leaves them protected but visible. The glass itself is visually notable not just for its dished profile, but also by its high degree of clarity and for its resistance to fingerprints.

The result is a stylish, high-quality and solid feeling build. The glass driver covers certainly add visual appeal, even if that’s not the principal reason for them. They look and feel the part of a $2,399 headphone.

Accessories

In addition to the headphones themselves, the HD820 package includes a sturdy storage case, a microfiber cloth, instruction manual, three cables, and a USB flash drive.  That drive contains a copy of the manual in PDF form and a diffuse-field frequency response curve for your actual pair of headphones; this is the chart for my particular pair:

I’m not sure how useful this really is as it is fairly coarse and cuts off at 12 kHz, but I suppose it might be relevant for comparing to the “reference” measurement and to the charts provided with other units. 

The included cables are all the same 10ft (3m) length and cover the ubiquitous 1/4” (6.35mm) TRS stereo unbalanced connection, and two balanced connection standards - 4.4mm Pentaconn TRRRS, found increasingly on both Sennheiser and Sony electronics, and the more common 4-pin XLR. Each cable has a soft, pliant, cotton sheath, and is flexible enough that they do not result in microphonic behavior. If bought separately, these cables run from $200 to $275 each.

Comfort

The pads are quite plush, with what seems to be a protein leather surround, a microfiber face and are about 3/4” thick - this makes it easy to get, and keep, a proper seal, which is important if you want to get the best out of these. There’s plenty of clearance around my ears and no contact with the driver/padding on the inside. Clamping force feels a little higher than the HD800S, but is otherwise just sufficient to keep them planted and is much less apparent than with, say, the HD650 or the Focal Utopia.

I’m used to having some degree of heat build-up with most closed-back headphones, though less so with more recent flagships, but notably with the HD820, I have not run into this at all.

While a little more physically substantial overall, and being 10% heavier than the HD800(S) at 12.7 oz (360 grams), they’re equally comfortable. So comfortable that I can wear them for hours straight, even on hot, muggy, Seattle afternoons, with no trouble at all.

Sound

At the simplest level, the fundamental signature of the HD820 follows a modest “W” shape in terms of frequency response. The bass is tastefully elevated vs. neutral (or the HD800(S)), the mid-range has a modest bump that helps maintain presence and balance and a little extra energy in the treble goes a long way to keeping things open and airy.  They are unmistakably HD8XX series headphones.

 

Tone & Timbre

While not perfectly neutral, tonally, the modest deviations here do not result in any obvious issues with the reproduction of instruments or voices. Discerning a violin from a viola, in a complex orchestral piece, doesn’t require any concentration. Cymbals have very natural sounding impact and splash, with no steeliness and perfect decay. Discordant brass (Miles Davis getting carried away with his “horn” comes immediately to mind) retains its natural bite and edge while remaining completely natural when played less aggressively.

Instruments sound organic and have appropriate body, tonal weight is as good as I’ve heard, and music has real presence. Whether it is conveying the “woodiness” to deeper notes on a plucked double-bass, the bite and shimmer of a harp or the subtle variations in the boom from a timpani as the beater hits in different places; these cans do an uncommonly excellent job of rendering it all realistically.

Bass

Sub-bass is powerful but controlled and while perhaps not exhibiting the absolute lowest, deepest, growl and rumble that, say, the Abyss AB-1266 Phi CC or Fostex TH900 Mk2 are able to portray, they’re not far off and are more than capable in this regard; it’s only in an immediate comparison that you might be aware of the difference enough to care.

Fire up something like Beyonce’s “Partition” or Trentemøller’s “Chameleon”, both tracks that I like to use when assessing bass performance (they’ll rapidly over-pressure my listening room if played loud on my speaker system), and you’ll quickly hear just how cleanly and deeply these things can play, as well as being treated to an excellent display of bass texture and delineation.

Bass rendering is very well textured, taught, fast, punchy with slam and impact rivaling the better planar designs. Natural reverb is conveyed well with no exaggeration. Following a tuneful, nuanced, bass-line is easy. And the end result is a very foot-tapping, high-energy, delivery and a very solid foundation upon which an overall piece can rest.

Bass/Midrange “Bleed”

There is no bass-bleed into the mid-range (a common issue with closed-back headphones). A dip in the frequency plot around 250-300 Hz is likely partly responsible for the clean, audible transition and integration between upper-bass and the bottom of the mid-range. With the rest attributable to well-tuned bass ports internal to the driver surround.

Even boosting the bass, significantly, via software EQ does not result in any bleed into the midrange. Not that you really need to do this, unless you’re a total bass-head, as the slightly elevated bass levels are more than satisfying as they are. In comparison, even without bass-boosting EQ, the TH900 Mk2 and the Sony MDR-Z1R have issues with bass affecting the mid-range; the latter more than the former.

Midrange

When I first saw the frequency response plots , and initial show reports, of the HD820, I was a bit concerned here. I’d read that there was some nasal quality to vocals or “honkiness” in the mid-range. My concerns turned out to be unwarranted and I’m not hearing that at all. While the mid-range is pushed forward in the mix a little, this simply serves to bring it into better balance with respect to the slight elevation of the bass and treble regions.

Vocals, whether it’s Leonard Cohen, Michael Jackson, Mary Black, Kate Bush, Bjork, Tracy Chapman, Ian Dury, Dusty Springfield, Trent Reznor, Tori Amos or any of the myriad other’s who’s music I’ve listened to here in the last two weeks, have been uniformly excellent, without so much of a trace of “nasal” quality nor anything I could describe as “honky”.

Instrumental and vocal elements are easily separated while retaining a fully cohesive presentation. There is a liquid, effortless, sonorous aspect to the way the HD820 handles midrange tones - and they do it without trespassing into the realms of coloration or euphony.

A smooth, resolving, and even-handed delivery, with excellent integration across the transition bands, yields amazing transparency, a natural sound and superlative resolution. Midrange technicalities are similar to those of the HD800S and the Focal Utopia and remain uninhibited by any interactions with the driver enclosures. Absolute resolution here is a hair below both of those models but is close enough that unless you own both, you won’t know, and even then you’ll likely have to listen specifically for the differences.

Treble

Like many closed-back headphones, the HD820s deliver a bit more energy in the treble than is strictly neutral. This is often taken too far in an attempt to avoid a “closed in” or “veiled” sound (the Fostex TH900 Mk2, in particular, come to mind). But here it’s “just right.” Yes, it’s more prominent than a purely neutral transducer would yield, but it works.

There is a tangible sense of air and space to the way the HD820 renders music, particularly noticeable with naturally recorded acoustic pieces. This comes across extremely well in the sense of space of the venue, and general ambiance, with the Cowboy Junkies “The Trinity Session” - a piece recorded with a portable DAT recorder and single microphone (so no “stage” or “imaging”). The Sennheiser’s deliver an unusually vivid sense of the space the recording was performed in.

Beyond the acoustic effects, the upper registers are both fully extended and very smoothly portrayed, with absolutely no grit or grain in evidence. Torture-track vocals/songs, be it Julia Fordham (in her self-titular debut), or over-sung mid-80s glam-metal/rock, there’s not a hint of sibilance or strain. Try as I might, I couldn’t find a single track that resulted in anything unpleasant in the treble that wasn’t already part of the recording (e.g. deliberate distortion, or audible edit-points, in some earlier “Prince” work).

 

Resolution, Detail, Dynamics and Transient Response

Much like the striking, concave, glass driver covers/reflectors, the fundamental delivery of the HD820 is extremely transparent. Yes, the HD800S and HD800 are even more transparent, but it’s only in back-to-back comparison that this is apparent. You can hear deep into the mix, layer by layer, element by element. If you want something more resolving of details, better able to render micro-dynamics, or with better transient response then your only true options are found in the flagships of the open-backed world.

Micro-dynamics are often easier to hear with closed-back headphones, simply due to them being innately subtle and the quieter background resulting in a better audible dynamic range. Here they’re excellent. Tiny shifts in vocal inflection/reverberation, especially with gravel-tones (Leonard Cohen and John Lee Hooker, being two notable examples) or the uneven draw of a bow over strings are readily discernible and add real texture and nuance to the presentation.

Listen carefully, and you can hear the subtle shifts, in the already quiet note, resulting from the triangle at the beginning of Tanita Tikaram’s “Twist in my Sobriety” being hit inconsistently. At the other end of the scale, the impact from high “energy” electronic instruments, “percussion” included, as well, of course, as with big orchestral works or even cannon fire in the 1812, macro-dynamics are excellent and very much make you "sit up and take notice".  There’s plenty of slam when it's needed, and large, rapid shifts in level are clean and crisp.

The instant emergence from silence with a drum or cymbal strike, or the pluck of a string, speaks to excellent transient response. In new pieces, it can be quiet startling at times. And this is coupled with no exaggeration of instrumental decay … you can hear a single string pluck, or cymbal strike, gradually ebb away into silence without the sense that you’re hearing artificial reverberation or resonance (not always the case, with, say the HD800).

Stage & Imaging

The HD800, and to a lesser extent the HD800S, are known for projecting a large stage and for excellent imaging (by headphone standards). The ability to do this is a typical Achilles heel for closed-back headphones, and more often than not they wind up sounding closed in with a compressed, flat, stage. While the HD820 doesn’t quite manage to project as expansive and vivid a stage as its brothers, it still exhibits a markedly bigger, better stage and more vivid imaging that many well-regarded open-back headphones.

Listening to “A Case of You” (Diana Krall, “Live in Paris”) provides a tangible demonstration of how well the HD820 can place sounds within the stage … be it noises in the background, the piano, Diana’s voice, each emanates from its apparent place in space with absolute solidity.

I’m hard-pressed to name another headphone at all, open or closed, that does a better job with stage and imaging (excepting the HD800(S), of course) - perhaps the Abyss AB-1266 Phi CC pulls it off, but that’s all I can come up with. You’d simply never know these were closed-back cans by this measure - the spatial cues are that good.

Isolation

The principal raison d’être of a closed-back headphone vs. an open-back model is to keep their sound in and keep external sounds out. One particularly positive side-effect of keeping external sounds out is the ability to listen at lower volume without losing low-level details and preserving similar audible dynamic range. While there are some other sonic-traits that tend to go hand-in-hand with closed-back models, such as elevated, more impactful, sub-bass/bass delivery - which can make them preferable to some for certain, specific, musical genres - in general, closed-back headphones are regarded as a sonic-compromise.

So, while some will opt for closed-back headphones for their tendency to emphasize bass, and frequent U-shaped signatures, my use for them is for the isolation. I often listen at night, via a laptop and a Hugo 2, and while I could use IEMs for this purpose, I prefer the comfort and ease of donning/doffing proper over-ear headphones (vs. IEMs):

 

The HD820 provide enough isolation for me to listen at fully enjoyable levels while my fiancé is dozing beside me, without disturbing her in the slightest. At my normal listening levels, around 80 dB, she can’t hear anything at all even with much higher musical peaks. And as she’s come to talk to me while I’ve been listening for this review I’ve not heard her at all, either. She has taken to coming up behind me and scaring me out of my seat - something she absolutely delights in, and that does not work for her when I’m using any of my open-back cans.

Closed-Back Comparisons

My principal comparisons here are going to be to my other flagship closed-back headphones, which I keep around both for their different musical abilities and strengths, as well as to have a broader set of references when doing comparisons. From left to right we have the ZMF Eikon (in Padauk), the Sennheiser HD820, the Fostex TH900 Mk2 (Emerald Green) and the Sony MDR-Z1R:

vs. ZMF Eikon (Padauk)

These are clearly the most neutral of the bunch. They’re not very far ahead of the HD820 in this regard, but they are more tonally pure nonetheless. Despite this, they still have a very slightly warm tilt to them.

And while the tone is lovely, when it comes to other technicalities, the Eikon are rapidly eclipsed by the Sennheisers. Most notably, resolution and micro-dynamics, stage and transient response are better with the HD820. The Eikon will sometimes seemingly gloss-over, or subdue, details that are readily discerned with the TH900 Mk2 or the Sennheiser units.

Their sound is very smooth, balanced and natural, and they are well suited for losing oneself in a piece of music as a whole but are not on the same plane when it comes to revealing all the detail and nuance in a piece. And the more complex the arrangement, the more this becomes apparent - and this is especially the case when compared directly to the HD820.

vs. TH900 Mk2

The TH900 Mk2 possesses what I can best describe as a “fun” signature - which is somewhere between a prominent “U” shape or a “W” with a smaller central peak. Bass is significantly emphasized, though remains taught and punchy with significant slam and impact and excellent low-level rumble. Sadly, it also tends to bleed into the mid-range, which is already somewhat recessed compared to the frequency extremes - and as a result, these do not fair as well with vocals or mid-centric pieces.

Upper registers tend towards being quite bright, and certainly a lot brighter than the HD820, but this doesn’t result in the same sense of openness, air, or space when compared to the Sennheisers. The brightness here is less noticeable when its part of bass-heavy productions (EDM and other similar electronic music). Both aspects still tend to overshadow the midrange, however.

Technically, the HD820 out-resolve the Fostex unit, especially the midrange, be it in raw detail or micro-dynamic prowess. And the Sennheiser cans have a vastly more apparent stage - the TH900 Mk2 sound closed in by comparison. These Fostex are much more a bass-head can, or for those that listen to a more limited selection of music and like a “U” shaped signature to go with it and add a bit of spice and punch. Swapping in pads from the TH610 improve things quite a bit, but they’re still not on the same level as the HD820.

vs. Sony MDR-Z1R

At almost the same price as the HD820, and being similarly well built, the Sony’s turn in a disappointing sonic performance. Where the HD820 are well balanced, the Sony is extremely warm, and bassy. Where the HD820 has taught, fast, punchy bass, the Z1R is under-damped, bloomy and even boomy at times. Unlike the HD820, the Sony’s bass intrudes into the midrange sufficiently that it makes for a heavy, if not quite muddy, sound. And where the HD820 has nicely integrated top-end, the Sony’s sticks out enough to notice … often adding glitter or zing where it really doesn’t belong.

These can be a nice, nighttime, listen, with the right music, when you want something relatively mellow, and still want to hear the details, but they’re too far off tonally, with too many issues affecting the midrange and bass, for them to be truly competitive with the other cans here.

Oddly they pair quite well with the Sony NW-WM1Z DAP (which is a very neutral and capable player, so I’m not sure why that works out,) so I keep them around for bed-time listening with that player.

Drive & Amplification

The HD820 call for a proper headphone amplifier and will reward any investment in such with excellent scalability. You don’t have to go overboard to drive them well; at a minimum, having additional power on hand seems to significantly improve their bass performance, slam, and impact, and results in an even-more effortless sounding delivery, but they will provide a very revealing window into your music allowing more capable amplification and sources to really shine.

These were reasonably at home being driven straight out of the balanced connection of a Sony NW-WM1Z (on high gain), but stepping up to the Hugo 2, which has about double the power, gave an easily-audible improvement with respect to drive authority and sense of scale.

Both the Massdrop x Cavalli Tube Hybrid and Liquid Carbon X, paired with either of those sources, improved things further, with the CTH increasing the sense of space and the LCX having better grip and a punchier, tighter, bottom end.

When paired with either the SPL Phonitor x or the Woo WA234 Mk2 MONO (Cathode Output, High Z) they took another step forward, with bass definition and sub-bass drive jumping up several notches, depth and layering of the stage taking on an otherworldly palpability, and also revealing the HD820’s impressive resolution and micro-dynamic subtlety.

The Sennheisers were also fabulous straight out of Chord’s DAVE. While occasionally I felt the HD800S benefitted from an external amplifier vs. the DAVE’s direct headphone output, I never got that sense with the HD820.

Summary

There are no two ways about it - the Sennheiser HD820 are the best, all-around, closed-back headphones I’ve heard. While not perfect, and certainly not inexpensive, they’re simply the most capable and enjoyable headphones of their type that I’ve had the pleasure to listen to. I am quite sure they’ll be getting by far the lion’s share of my closed-back listening time.

Don’t come into this with an expectation that you’re going to be getting something that sounds identical to an HD800(S) but with isolation, or you’re likely to be somewhat disappointed - even though the HD820 are the closest to meeting that goal of any available headphone. In a direct HD800S comparison, the question of value is going to be unavoidable. For sure, the HD800S (or HD800¹) are better value, offering slightly better sonic performance and being 2/3rds the price. At the same time, it’s an apples-to-oranges comparison. Unless you can only have one pair of headphones, you don’t buy closed-back cans to do an open-back headphone’s job.

If what you want/need is a well balanced, highly-resolving, technically excellent and musical closed-back headphone, and accept that it is likely that such things will never perform quite as well as an open-back design, then the HD820 is simply the best game in town.

I am extremely pleased with my pair, they are definite keepers, and if I was going to limit myself to a single closed-back model, there is no question that it'd be the Sennheiser HD820 that I'd been sticking with.

In short, as far as I am concerned, the Sennheiser HD820 represent the current state-of-the-art for closed-back headphones, and are highly recommended!

-Ian Dunmore (@Torq)

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1. Once modded and appropriately equalized, which I consider mandatory for the HD800; I do not get on with them in their stock form. ↩︎