Sennheiser HD 6XX vs. Hifiman Sundara SHOWDOWN REVIEW

Hi all,

I know that a lot of people compare the 6xx and the Sundara and wonder if they should get one or the other, so I thought I’d add my experiences in the hope that it might help someone. Also I’m dying to talk about how these two headphones sound compared to each other.

Disclaimer

I’m a novice to audiophile gear, and have only a heard a tiny fraction of what’s out there to compare things to. My opinions here are all entirely subjective and my own and your mileage may vary etc. My ears will be different from yours.

I used both headphones with the same combo:

Dac: JDS Labs DAC+
Amp: Rebel Audio RebelAmp
Music Source: Qobuz via Roon

I have tried the Sundara on the Zen Can and the Atom Amp. As I note below, I thought the treble could be a bit harsh on the Atom Amp on some tracks, but the extra warmth of both the Can and the Rebel tamed them (with the Rebel sounding significantly better, but you’d hope it would for the price).

I’ve heard that the 6XX in particular can take on different characteristics based on the amp you use with it, but I don’t have anything else to test it on right now, so keep that in mind. Everything I say below might be different if you use a different DAC and amp.

Background

I’ve owned a Sundara for a while now and decided I wanted another headphone. The primary reason is comfort–I love the way the Sundaras sound, but they’re heavy enough to become wearying after wearing them all day, which is what I’ve been doing since I’ve been working from home.

The Sundaras also seem to put too much pressure where my jaw meets the rest of my skull, which is particularly sensitive, and even after bending the heck out of the metal band at the top, it’s still noticeable especially after long listening sessions.

I was varying up the Sundaras with KSC75s which I modded with a headband and Yaxi pads. It doesn’t get much lighter than that, and they felt like air on my head. KSC75s sound amazing for the price, as is well known, and they’re obviously fine for Zoom meetings and such, but I just I wanted something that sounded better for long-term listening.

The obvious place to go here is Sennheiser, who make some of the lightest audiophile headphones around which are still considered among the best. It’s crazy to me how most audiophile headphones are so heavy, 350 grams or more, and its barely mentioned in reviews. And most of the time all this weight is not due to anything related to the drivers or performance, but just because they put metal all over the things to make them more durable and “premium”. And sure the metal on the Sundara looks cool, but personally I’ll take light plastic over heavy “premium” metal any day of the week.

I did have a little bit of a chip against Sennheisers, though, because there are people who hang around various audio Discords and actually bully people into buying them, and will put up vomit emojis if you say you like a headphone they don’t and tell you the Sundaras are bad and say maddeningly dumb things like “soundstage is for speakers”. (Fortunately, this forum seems to have kinder people than the Discords or some other places I could mention.)

Anyway, I shouldn’t let annoying people determine what I should and shouldn’t do with my life. And so looking into the line, the HD-6xx seemed like the right choice for me both for its relatively low price and its reputation as a relaxing and warm headphone.

Comfort

I’ve already mentioned my issues with the comfort of the Sundaras.

The biggest problem with the Sennheiser from a comfort perspective is that the pads are just too hard, especially compared to the plushness of the Sundaras. I think I can get used to the pads around my ears, but the stock pads at the top of my head are just intolerably hard. So I replaced them with the Dekoni nuggets, and now they feel wonderful. This might create more hotspots, but I think it’s worth it overall not to feel like I have two elbows jammed into the top of my head. (As with everything here, YMMV.)

For the ear pads, since they supposedly wear out after about a year anyway, I think I’ll wait until that happens and then try the Dekoni ones to see if I like them any better. I know they might change the sound a bit, but what can I say-- I’m more precious about comfort than I am about tonality.

The Sennheisers are famous for having intense clamp force, and this is true, but I followed online instructions for bending the metal parts and got them to feel fine. Meanwhile the weight of them is everything I hoped for and there’s no uncomfortable pressure on my jaw at all. Altogether, I’m pretty happy with them.

Sound

I found the experience of switching back and forth between the Sundaras and the 6xx to be absolutely fascinating, in how good they sound in different ways.

I expected the “Sennheiser veil” effect to be subtle, given the way people talk about it and even insist that it doesn’t exist. It’s not subtle. You switch to the Sundara and instantly you’re hearing much more treble on the same track. Cymbals have a life and character on the Sundara that they just don’t have on the 6xx, as do high pitched synthesizers and strings. Maybe the effect is more subtle on the HD 600, maybe the Sundaras are just trebly, I don’t know. (I did try the DT1990 Pro in a store, and I can say that the treble on the Sundara is nothing compared to those, which I found unpleasantly trebly.)

That all said, as I mentioned when I previously had the Atom Amp, which is more “neutral” than the RebalAmp, I found the treble on the Sundara could get harsh, especially on distorted drums and synths. A song like “Time to Pretend” by MGMT which has a distorted synth line all the way through was almost intolerable to listen to. The warmth of the RebelAmp was a relief in this regard and really smoothed and warmed up those sounds and made them pleasant. However, I don’t think I would have had that problem with the 6xx since it’s so much warmer out of the box. Still, the 6xx seems to get along with the RebelAmp just fine, taking to its warmth and richness.

I found this EQ profile for the 6xx on Head-Fi and I like the extra treble and sub-bass it gives to the 6xx:

6xx EQ profile:

I also tried Amir from ASR’s EQ settings on my Sundara, but found it sucked the sparkle out of them so stopped using it. Maybe I can try a different one some time, but I like the stock sound of the Sundara so much I’m not sure I care.

The 6xx had a wider soundstage than I expected given the reviews, but it’s still nothing compared to the Sundara which puts the sound all around you so you’re just floating inside of it. The Sundara also has so much more clarity and airiness, you notice and can pick out each instrument in a way you can’t on the other headphone.

One place where the 6xx excels is “punch and slam”. Songs with driving rhythms just rock on it. And what people say about the tonality of the midrange of the 6xx is true too, vocals sound stellar. This is especially true on songs that focus on vocals, like Joni Mitchell’s “Both Sides, Now” which has a fullness on the Sennheisers that it just doesn’t on the Hifimans. The punch and midrange of the 6xx can make the Sundara sometimes feel lifeless by comparison. And while cymbals and strings have more character on the Sundaras, bass instruments have more character on the 6xx and become much more noticeable.

Sometimes the 6xx’s punch can be off-putting, though. There’s a strangeness of getting a thumping kick drum on a delicate folk song like Simon and Garfunkle’s “The Boxer”, for example. I had the same issue with “Cruel” by St. Vincent, where the kick drum just became overbearing, while these songs sound great on the Sundaras.

Lots of other rock albums though, like Little Fictions by Elbow sounded distinctly livelier on the 6xx, while the Sundara felt a little washed-out on it. And an album like The Fall of Chronopolis by Hedersleben I found boring on the Sundaras and super fun on the 6xx, and I feel like the headphones have given this album to me.

Moving to the harder stuff, on something like Tool’s “AEnema” the power and muscle of the 6xx really shines. It almost sounds like two different songs between the two headphones–on the Sundaras you get this beautiful effect where the toms are spread out all around you and you pick up all these little details of the recording, but everything feels detached and distant. The 6xx, on the other hand, just thunders through and gives you that head-bobbing effect.

A mellow Jazz song like “So What” by Miles Davis sounded better on the Sundara’s, making you really feel like you were in the room with the musicians playing all around you. I also seemed to like “Plainsong” by the Cure better on the Sundaras with its sweep and grandeur, which surprised me–the 6xx made it sound too muddled and the instruments too same-y. I put on “Reflektor” by Arcarde Fire and it sounded better on the 6xx, but “Joan of Arc” from the same album sounded better on the Sundara. (Actually it’s not even that neat–the first 60 seconds of “Joan of Arc” sounds better on the 6xx, but as soon as the strings, synths, and backing vocals kick in, the extra treble from the Sundara changes everything. In the end, I actually think I could be happy listening to the song on either headphones.)

And something like Pink Floyd’s “Dogs” which is not particularly hard but still depends on this driving propulsive feeling, it’s more active and compelling through the 6xx. “The Chain” by Fleetwood Mac also sounded better on the 6xx for similar reasons.

I was surprised when I put on a Grateful Dead album ( Blues for Allah ) and liked it better on the 6xx, but put on a Jethro Tull album ( Thick as a Brick ) and found I liked it better on the Sundara. Most jazz and orchestral soundtracks/classical I tend to like better on the Sundara, but classical music with a single instrument, like a piano sonata, I like better on the 6XX where the tonality is front and center and the soundstage matters much less.

The 6xx also seems to be more forgiving of suboptimal mastering, while the clarity of the Sundara exposes everything, good and bad.

Conclusion

At its worst, the Sundara sounded washed out and lifeless compared to the 6xx. And at its worst, the 6xx sounded like a muffled cave compared to the Sundara. This depended not only on the genre, band, mastering, and individual track, but also sometimes just on my mood, which goes to show how subjective and weird “what sounds good” can be. And at their best and with the right music (and mood), both headphones could be breath-taking and shiver-inducing in how excellent they sound.

I can see why some people talk about these two headphones complimenting each other. They bring out different things in the music you put through them. It can even be tough sometimes when you’re listening to a song and realize one part would sound better on one headphone and one part would sound better on the other. Of course, now I’m dreaming of something with the punch and mid-tone of the 6xx but the soundstage, treble, and clarity of the Sundara, but I’m betting I would have to climb pretty far up the price chain to find anything like that, assuming it even exists. I just don’t have the pockets for a Susvara or HD 800 S or whatever.

In the end, while I’ll use to the Sundara when I want to listen to certain music or just vary things up, the headphones that will probably stay on my head all day are going to be the 6xx, and it’s because of that one killer feature that most reviews barely mention in passing: the weight and comfort. We should have more headphones that weigh 260 grams.

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I’ve been looking at the Sundara for a while. May eventually pull the trigger to A/B with some of my Sennheisers.

I’m surprised you didn’t find the 6 series comfortable. Especially the newer headband padding. And I feel the newer 6 series headphones ear padding are stiffer than they used be. Even the suede feels a little different imo, compared to the older 580/600/650s.

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What can I say? I have a sensitive head.

I did see some people say that the HD 600 head padding is supposed to be softer than the 6XX, so maybe all 6 series are not the same.

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That’s interesting, I’ve heard the opposite haha. I like the newer style padding but that’s just me. We’re all different and like what we like.

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This is an excellent comparison!

You will have a hard time finding both punchy low end and planar like clarity. I spent months looking for it on the planar side. There are a few expensive sets that I haven’t tried yet, but I really don’t expect to find a good merging of the two at this point.

The search is fun though!

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Thank you for the excellent easy to read commentary! Very enjoyable to read with your logical reasoning to support your impressions.
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With my Sennheiser Massdrop HD 6XX being my least favorite headphone that I own, I suddenly have the urge to compare it to my Hifiman Sundara playing Joni Mitchell’s “Both Sides Now.” You can count on me pulling that up tonight to try to replicate your enjoyment of stellar vocals. And no one likes to rock out more than I, so punch and slam it is with some Audioslave tonight.

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I’d love to see your reaction on the day you try Focal’s headphones. They are way, way more punchy than the Sennheiser 600 family.

I often describe the 600 family as smooth and relatively subdued…

As your RebelAmp is really good, you might want to next try different DACs and see how they affect both headphones. The ESS9018 in the JDS Labs DAC+ is on the bright and analytical end of the spectrum.

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Let us know what you find! Your results might be different than mine, and I’d be interested to hear about them.

I might, but considering my dislike for the Sennheiser Massdrop HD6XX, you know what they say, “If you don’t have something nice to say, then …”

It’s certainly possible the 6XX only seems punchy and slammy to me because I don’t have other things to compare it too that are punchier and slammier.

What DAC would you recommend?

I’m happy with my Bifrost 2, but it’s $699 and involved a 6 week wait. I’m also happy with my iFi ZenDAC for casual listening and its price ($129 to $159). Both have richer and warmer profiles (certainly not bright, edgy, and analytical), but the Bifrost 2 involves more layering and complexity. I’ve found that some brightness perceived on ESS or AKM DACs transforms into resonances or room atmospherics with these two.

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Funny thing is I used to have the Zen DAC and I got rid of it because I was so mad when I watched the Golden One video and saw that the filter they used imitated MQA (though I’ve since discovered you apparently have to do a specific firmware update for that to be the case?) I also felt like I was paying extra for MQA and all the extra features like the amp and balanced architecture and the bass boast and so on that I didn’t need.

I’ll consider the Bifrost but that is a little expensive for me right now. Thanks for the recommendations!

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I long resisted iFi’s products (just toooooooo weird, use nonstandard terms, and it’s hard to penetrate what they actually do). However, I wanted a Burr-Brown chip and they use Burr-Brown.

The ZenDAC is a good DAC at the price, but fails for not having a strong amp. It looks like an all-in-one from the front, but is correctly named “ZenDAC.” The amp doesn’t have enough power to generate deep bass, and so they overcompensated with an exaggerated shallow bass boost button. The boost works well enough (tolerable) on the HD-600, but would be excessive on the HD-6XX. Indeed, Drop has a 6XX edition.

I’ve come to also realize the ZenDAC’s value as a low-cost balanced source and role as a preamp.

While I never liked MQA and that video drove home the point, a lot of such monkey business is not very audible on lower end equipment. The main factors are chipset, and then roll off filters for the high end. Some ESS and AKM DACs leave in harsh artifacts.

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I am listening to Joni Mitchell’s Both Sides Now through Sennheiser Massdrop HD 6XX connected to a Schiit Jotunheim. I hear the weightiness of her voice like I would a man’s voice. I am not at all implying that she sounds like a man. I am only making an analogy to describe an enjoyable vocal characteristics that I may have not appreciated before. The heaviness is enjoyable.
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Switching back to Hifiman Sundarais connected to a Headamp Gilmore Lite MK2, the heavy weightiness of Joni Mitchell’s voice is gone. With this track, I hear her voice lighten with added crispness which really makes sweetness flow through my ears and into my emotions. I much prefer this lighter detailed treble vocal presentation which I think enables the song move me. Taking account of the other instruments playing, I also perceive an enveloping flowing stage that brings me deeper into the song.
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Ultimately, with the Hifiman Sundara I am emotionally moved throughout the entire song. Conversely, the Sennheiser Massdrop HD 6XX sounds like an entertaining performance, but lacks involving me emotionally with only just a fraction of emotional involvement at the resolution.

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Totally valid response.

I feel like for me the weightiness of her voice on the 6XX gives it the richness that I like, it sounds ‘fuller’ to me and I respond to that.

But I can completely understand preferring the lightness of the Sundara here.

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650 really shines on a tube and scales very well with higher gear. I’d also like to try the Sundara soon to compare. May look for some deals.

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Sennheiser Massdrop HD 6XX on my seventh track of Audioslave. The slam you speak of is there. I A/B with the Hifiman Sundara and it cannot compete with the Sennheiser Massdrop HD 6XX with these rock tracks. I turn up the volume on the Sennheiser Massdrop HD 6XX and feel the show and the head banging begins. Slip on the Hifiman Sundara and the shrillness forces me to turn it down immediately. I have often experienced this ability for Sennheiser Massdrop HD 6XX to be turned up very loudly compared to many other headphones. So, listening to treble and high mid focused headphones, I usually put the volume low compared to most listeners. I think that many Sennheiser Massdrop HD 6XX fans may listen at higher levels than I. Sennheiser Massdrop HD 6XX is a great headphone for those that want to listen at very high volume levels, which I do not. Perhaps this is why I love my Beyerdynamic DT880 so much. Because I listen at lower volumes.
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Back to Sennheiser Massdrop HD 6XX. So, even though I am rocking out at a louder than usual volume than I am used to, I can’t help but hate the lack of treble liveliness coming from Sennheiser Massdrop HD 6XX while rocking out to Audioslave. It sounds sort of dead. So, I enabled the equalizer preset on HeSuVi for Sennheiser Massdrop HD 6XX. This brought Sennheiser Massdrop HD 6XX to LIFE. Now it is absolutely rocking out with the fidelity that I have always been missing. I highly recommend this equalizer to anyone else that also finds the Sennheiser Massdrop HD 6XX dead and lifeless.

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I’m so happy you found a way to like your least favorite headphone!

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BTW, I am now running Sennheiser Massdrop HD 6XX on DarkVoice 336SE WITH the EQ and they have never sounded better.

Rockin out right now.

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I do find the 6XX the darkest sounding among the HD-6 line. Never heard the Sundaras but I’d think the best comparison is against the HD600 instead (neutral-bright).

Even the 600 vs 6XX/650 have differences – besides tonal balance. To my ears, 650 drivers are more aggressive sounding than the 600 (and against the 58X too). On the other hand, bass heads will certainly hate the lack of low end in the 600. :man_shrugging:

As far as added harmonics on tube amps, HD600 also scales by a lot.

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