Superlux HD-668 B

I had trouble picking a rating for these.
 
At the price I paid ($36), these sounded good in many ways, with the exception of the highs, which I found to be harsh.
 
The killer for me, however, was not the highs themselves, but the ear-stabbing pain those highs induced very quickly (within a minute). This wasn't fatigue - this was pain. I'm not set up to measure anything, but I suspect they have a nasty spike somewhere in the treble range.
 
Fair warning - my taste doesn't lean to aggressive bright highs (lean more to HD600 or X1 signatures).
 
Leaving that aside (which obviously I couldn't), bass and mids were pretty decent for the price.
 
I found the fit to be quite comfortable (and I'm picky about fit).
 
If you have any issues with listening fatigue, I suspect you are going to find these unlistenable.

Fist of all, this is my first ever review,and English is not my native language, so please, have some understanding .
 
I bought these headphones 9 months ago, they were my first "quality" headphones. Before them I owned some pretty old phillips headphones which my dad boght back in 1994 when he bought our Technics amp,cd player,and tape deck player. The price of these headphones was around $50 , and I like good quality sound for a budget, so I decided to get them. I was by no means an audiphile back then, but these headphones brought me into the world of audiphiles. For the price, these headphones are very good. They deliver clear and crisp sound in most cases, bass response is very good, but the thing I didnt like about these headphones was the fact that these headphones are not really neutral sounding ( for my taste ).. They tend to lean towards higher frequencies, and that bothered me so much because this made the mids sound not as good as you would expect from monitor headphones. All in all, you get what you pay for, a good headphone that delivers great sound for the price. is nicely built , is very comfortable and sturdy and it definitely wont dissapoint you no matter how you use them.

Let me start by saying I don't normally write reviews on the official level, star system with graphs and all. I do look at them religiously when trying to find info on a HP, DAC, or AMP that's sparked my interest. So here I am reviewing on the Taiwanese made Superlux 668B which is quite obvious a mix of AudioTechnica's wing headband system, AKG K studio series body, with Superlux's driver. Aside from the last bit, obviously all are homages or clone of their respective brands. Not the first time one brand took from another however.

With that out of that way, let me start by saying at less the $50 shipped, not much can go wrong. The headphones look and might feel somewhat cheap on the cups but before you judge, plug the sucker in and have at it.

Notes:

- Quite obviously the headband's wing system is something you'd find from AudioTechnica's line. Similar to AD900X and the likes. The headphone feels quite secure but the the two wings takes time getting used to. I'm hoping with time they get somewhat softer and less obvious. Aside from the two wings pads, the headphone is very light and does not feel like you're wearing a headphone at all. Clamp force is very good in gripping your head but not overly where it hurts (like a DT880 Pro when new). I've tried pointing my head downwards to try and get the HP to fall off, doesn't even budge. For reference I wear a 7 5/8" fitted hat, I fare on the big noggin side.

- The cups are made of plastic, they feel and look cheap. Aside from the opening of the grill, the cups look exact clones of the AKG K studio series (K240 for example). From the way the cups swivel up and down on the driver housing, the way the headband goes into the housing, as well as cable entry and run from one driver to another.

- The earpads are pleather and aren't too bad, although I can see some Hifiman velours or similar would do great on comfort. As is, it's not too bad. They're soft but not memory foam or anything fancy. The feel isn't too bad either, I've seen worse.
 
Now the most important part, SOUND.

They've been running for about two hours now and there's already a noticeable difference in treble. At first it sounded rough and spikey but after 60 mins it's calmed down quite a bit. From word around here, 50 hours would produce the final sound after burn-in. First these are what you would call reference type headphones, neutral sounding and fairs to the bright/airy side. No dark stuff here and if you seek a bass-head or a warm phone, look elsewhere. What I can say however is the clarity on these phones are fantastic. Dry sounding, it pairs well with tube amps for a more musical flavor but does well with solid state if speed and attack is of priority. With an emphasis in the treble end, they air on the bright side  The treble does get too hot with poorly mastered tracks, definitely a bright and airy phone that does well when the music fed is greatly recorded (loud war tracks need not apply). The bass has a steep roll off after 60hz, sub-bass rumble is non-existent but bass is pronounced from 60hz and up. Nothing sloppy, but unamped the drivers can lose control when the sound swells. Soundstage isn't very wide, I would say comparable to the DT880's semi-open width. Instrument separation are great, you can easily follow different instruments in a piece without it getting lost when you've got 3-4 different going at the same time.

These sound to be about 85% straight from a cell phone, a plus if that's all the source you have or need to use it on the go. When amped, the HP can keep things tight and true. It doesn't take a whole lot to get these going as well, plugged straight to my Lenovo laptop I'm having to use 50% of the volume bar to keep things at a sane level. These are 56ohms with the rating of 98db/1mW according to the box.

I've never heard anything in the full size realm that sound like these at this price range. It definitely holds up to the hype and praises it gets as reference or studio quality. If you prefer a bright tilted phone with a dry and clear sound at less than $100 this is something that should be in your shopping list. At the normal price of around $40, these are a steal of a headphone. It's great as a value minded HP, backup, or something to let the kids chuck around. I'm one for great value and willing to spend the money if it warrants it so when something with great value comes around it definitely sparks my interest. If you're looking for something that won't leave a hole in your wallet that will compare very to mid-fi headphones, this is it. A definite listener's headphone, not very show worthy but when your friends ask what you spent on it, you'll look like you've done some homework with your purchase.

I found that the headphones are fairly boring if you are a basshead, but with the an amp, they can really drive, but a bit muddy at high volumes.

Hi,
I did test the HD-668B on my modified SMSL SD793II dac & headphone amp
where the sound is great and a bit more focused than the HD-681 (but both headphones are close)
After listening the HD-668B, the HD330 has too much bass with overall heavier sound       
 
There is a lot of details, the voices shine.
The bass are deep & clear.
The trebles are very clear, when they are hard,
they only reflect the poor quality of the amp or dac
If you improve the quality of electronics, you will hear it through the HD-668 B
 
I am very impressed with the soud you get directly on a Samsung Galaxy S3 (Wolfson WM1811 DAC)
it is a pefect match, better than the 681 (too much spatial)
Jerome

Just generally good and hard to find fault with.  Not really deep low bass, but enough to be pleasant.  Mid-bass has good presence and there is excellent clarity and detail in mids and highs. I found soundstage to be a little congested and overall a bit of a "thin" sound.  While many people have praised these, I find them a little boring to listen to.  The highs do not have an audiophile-grade "zing".  Clamp force a bit high at first and ear pads could be more comfortable.  A little more closed than semi-open so soundstage is not that wide.

While sound is excellent I'm not a fan of knock offs and these are knock offs of AKGs and ATs.  If they had their own style I would buy more Superlux products, but their entire lineup seems to "borrow" design cues from others.  It's too bad, because sonically they're excellent though after some time of listening I did not enjoy the highs as much.  That tells me it's easier than we think to make good sound, but coming up with a great looking headphone - that's worth paying extra for.

I have many audiophile headphones like sony zx700,koss porta pro,soundmagic e10,pl 11,skullcandy uprock,. out of whole least nothing sound better than my superlux HD 668B. this headphone is must for audiophiles who want their instruments to hear every note with ease. guitar sound will blow ur mind. may be not comfortable as zx700 but sound is awesome. bass is adequate. goes deep and low but rumbling is not present as soundmagic E10. u can hear every sound with ease. bass does not disturb the whole frequency response. sound is neutral,no fake sound,lower mids slightly recessed. it has detaching cable of 1m and 3m respectively. u can remove the pads and change with akg 701. though u will not feel pain for 2 or three hours(sufficient for movies). these are open back headphones and sound leaks through it which is not a problem for me. sound is spacious with excellent instrument separation. if you want a sound for $150 in $50 then these are for u. may be they are not built strong but if u look on the heart of headphone which is its sound, these are above par and are better than grados.


if u want a true audiophile headphone then look no further.

Lot's of Audiophiles own these they but can sometimes be like a wild horse that needs taming gotta eq and lightly amp to get best out of them - five times as good as
Audio Technica ATH-ES-700's for example IMHO not as great as the UE 600's. Fiio E17 sounded really good with these. A Valve Amp like the Bravo even better 

I am upgrading from my Panasonic RP-HTX7s, which i thought were amazing but now....I have to take that back. I also thought they were huge but the HD-668Bs are much bigger. As far as the sound goes I can only compare to what I had so here goes..
 
I've had the Panasonics for over a year and they were beginning to sound different. The Treble became more pronounced and the bass was loose and distortedish...they werent blown just probably overused. I only noticed those issues at higher volumes. Nonetheless, out of the box these Superlux's are very bad as far as treble goes. I read the reviews and I was prepared to AMP them up and EQ. I used them with my phone for a little bit and it's true you can hardly hear the bass.
 
I found that lowering the 8K nob on EQ helped relieve the overbearing highs and made them sound balanced. I dont have an official AMP but I own a samson GoMic which if you've used one, you'd know that it pumps out some serious power from the output (atleast it did for my Panasonics). So with the combination of adjustments I couldn't believe the sounds I was hearing! WOW! sounds i never heard before. AND THE BASS?? I turned up the bass in the Samson GoMIC audio settings and these bad boys can pump some serious bass...and unlike my panasonics they can handle the power!! They don't even rattle at all even at full volume!! 
 
Overall I am very impressed and very happy with this purchase, I might even get a real amp for portability. I will keep this review updated if anything changes.

I purchased these at the end of December as a gift to my self (YEAIMLONELYSO). I did an unfathomable amount of research on headphones that were geared towards "gaming". I had my eyes set on the 555's and was about 30 minutes away from pulling the trigger, then these things popped up. $50 bucks, knockoff, cheap materials, why would I even consider them?
 
Holy asdkfljadslfds I am glad I did. The 668b's are not an "impressive" headphone, they are more of a honest, truthful headphone. These are considered "cold" as opposed to "warm". There is no hiding anything from them, if you have a ****ty file, you are going to get ****ty audio. There is no layer of icing catered onto whatever you are listening to. Time and time again I have heard crackling, and I became utterly pissed that I bought a knockoff, but guess what, I was listening to a sup-par audio file. 
 
When I first started playing with them, the hi's made my eyes water, but after about 40 hours or so of burn-in they have become tame. The mid's are fantastic, and excel extremely well for my original reasoning of purchase, gaming. The bass is (I would say) just about perfect. There is no lingering rumble after something hits the bass, it is tight, compact and kicks just the right amount. My favorite thing to do now is crank it up, sit back, and enjoy some music. I listen to a wide variety of music from electronic, classic rock, "rap" (or whatever modern rap would be called), country, some metal, and pop music every now and then just to impress my self with how well these things sound.
 
From what I have seen, reading reviews on headphones is the same thing as asking people if they like oysters or not (or some other acquired taste food). A person's enjoyment of audio seems to be as expansive as their enjoyment of taste. Please take this into consideration.
 
To conclude, I absolutely love these headphones. They are well balanced, easy to wear (after some break-in), and will never fail to impress me. I'm no audiophile, but I believe I can distinguish good audio from the bad. These were an upgrade from my UB3R L33T G4MING HEADSET, and my god were they ever. Ontop of that they were fifty bucks! 

I bought these after reading all the rave reviews on Headfonia and Head-Fi... here are my impressions of them.
 
I think any criticism concerning materials or craftsmanship of the HD668b is nitpick considering its price of $50 (easily found for less) - I personally haven't seen headphones in this price range that are this well built.
 
It's obvious that Superlux took elements from both AKG and Audio Technica designs. The way the earcups pivot is very nicely implemented and conforms easily to the shape of the head. As for the Audio Technica-styled "wings", I've been a long-time fan of it and prefer them to traditional headband design, so that's a plus for me. Add these on top of the two sets of detachable cords, a 1/4 in adapter, a carrying pouch, and an anti-yank clip... I am honestly quite impressed considering the 668b's price.
 
The packaging is simple but elegant; a very clean and professional presentation. The cords are carefully wrapped to prevent movement during shipping.
Construction is very sturdy. No rough seams in the plastic and nothing squeaks or rattles. I personally find the comfort level to be excellent as well; the wings provide just the right amount of down force and clamping force is just right. The pleather used on the earpads are above-average quality and are fairly soft without the stickiness of the cheaper pleather types.
 
Audio Quality
This is where I have a bit of mixed feelings about the HD668b... perhaps because I had too high of an expectation from all the rave reviews. Since so many calls it a "giant killer", I was expecting to be absolutely blown away, and I wasn't.
 
 
 
Treble: These headphones were extremely bright and harsh-sounding. It's strange that the review on Headfonia claimed the treble was excellent - granted, there's a lot of detail and when it behaves, the treble is quite sparkly. But as you can see in the FR graph there is a very sharp and pronounced peak between 5-6KHz, which is THE area that causes sibilance (overall the entire treble region is just way too pronounced to sound natural). I am not sure why Superlux tuned this headphone to accentuate this particular area, but I agree with Tyll's (from InnerFidelity) assessment on this one... it's like listening to a good headphone through razor blades.
 
Mid-Range: The quality of the mid-range is good, though a bit recessed. I think in spite of the issues with treble, the 668b's drivers are quite resolving and the mid-range does carry good clarity. It's just unfortunate that it tends to be drawn out by the distractingly sharp highs.
 
Bass: Contrary to the Headfonia review, I don't feel the bass is particular tight or controlled on the 668b, and bass extension leaves a lot to be desired (as you can see in the FR graph, the bass starts rolling off at 60Hz, and I certainly don't feel much sub-bass from these cans).
 
Sound Stage: The sound stage for the HD668b is quite spacious, likely owing to its detailed treble, clear mid-range, and its semi-open nature.
 
Instrument Separation: The HD668b performs well here; the drivers' good resolution allows the details in the treble and mids to be heard clearly. Orchestral music is properly layered and instruments are easy to pick out.
 
Isolation: Isolation on the HD668b is passable - not any better than the cheap $30 full-sized cans my wife had before this, but not bad considering its semi-open nature.  It should be fine for private use in homes or for sound work at a quiet studio. Do be aware that HD668b has moderate sound leakage, however - and may annoy people around you in libraries and whatnot.
 
The Superlux HD668 are a good pair of headphones when seen in the context of its price range. Design and construction are superb, as is comfort. Its audio quality is a mixed bag, and if this really is the only entry-level headphone you can afford, then be advised you will need significant EQ to make it sound pleasant.  Then again, for $50, I think the HD668b is still a good deal as long as you don't mind having to EQ them.  Personally though, I would save up a bit and invest in something in the ~$100 price range for a proper introduction into the audiophile world. First-gen Sennheiser Momentum, AKG K553, Audio Technica ATH-M50, or a used pair of NAD Viso HP50 are all excellent headphones that can be had for less than $150.

To be short, sweet and to the point, after lurking for some time and running pass to great reviews of a potential giant killer I couldn't resist. Plus with my SE-115s going out I needed something new so I took the plunge. So this is the neutral sound everyone was raving about. I simply love it! Besides to terribly miss-handled highs (seriously what on earth were they thinking) these thing show quite the detail. I have to rediscover my music. Oddly enough though I found the odd high end to help for some recordings, however it's easy to see how these could become fatiguing for some listeners, and that's not even to mention the clamping force. I can deal withe the highs but the clamping is what gives me head aches.
 
All in all, they are totally worth it.

It has been a LongLong time since i bought a remarkable product at such a low price. Full Stars for Value!
 
Soundquality wise, this headphone has great detail and clarity and WIDE soundstage. Instrumental separation is very good. Makes it a very good headphone for gaming(which i did.) It just sounds so nice that it can even compete with headphones in the $100-200+ price region. A REMARKABLE PRODUCT BY SUPERLUX. 

When I first put them on on I though that the highs will blow my head off. My ears got tired after 10 - 15 minutes. I though I would throw them out of the window. But having read some good reviews and advices regarding burning in the headphones I gave them a try. And now I must say WOOOOW.
 
After 8 - 10 hours of burning in (I left them plugged in to the computer, I put there some bass and treble heavy DnB and left for work). Whn i returned back, the highs became much softer, clear and completely bearable, and the bass was much fuller and deeper. I owned Senheiser HD 280 Pro and I have to say Superluxes are better. After proper burn in, when compared to HD 280s they have wider stereo range and more balanced overall sound. HD280s were more forward sounding, had worst mid frequencies and no full, deep bass.
 
You can definitely check your mixes on these and analyze musical work of others. Every detail is easily noticeable. I hope you will enjoy them the same way I do.
 

If you want to know how good these headphones are, consider that I have never written a review about any product I've ever owned. These should be at the top of the list for anyone searching on this site for a good pair of entry level headphones. Lots recommend the Porta Pro's and I am not one to say otherwise, but the design of the unit is somewhere around 30 years old and they haven't updated the materials. So I decided to go with these after looking on youtube and this forums for weeks. I've made a great choice and they sound great. Do not, for any reason, listen to anyone comparing these to $600 headphones. They shouldn't be compared. For $50 you will be blown away. For anyone looking for a $50 set of "cans" then you won't be disappointed by build quality or sound. They are great.
 
Pros.
Amazing sound for $50
They fit my big ass head.
Detachable cord
Two cord sizes that can connect and form one long cord.
1/4 inch adapter for your receiver
 
Cons
Make your ears sweat
Highs can be a bit much.
Puts a decent amount of pressure on the head
Do not isolate at all. These are private listening time headphones. Ambient noise will come right thru.
Open design so they naturally leak as bad as the isolation.
 
*************************Update
I've owned these for about 2 months now and wanted to do an update. I'd like to just warn dubstep and rap fans. These will not suite them. I'm a huge rap fan and listen to it often. The bass can't extend low enough to really sing with those genres. Don't get me wrong, they clear the fence but just by an inch. The highs have really relaxed after burn in. They are no longer piercing and fatiguing and have mellowed down. They can still use some adjustment based on the genre but they are livable now. Comfort is an issue now. They clamp pretty tightly and with the pleather pads being so stiff, it can get annoying. I'm thinking of getting the velor pads for these or try to change the padding. Seams like a lot of complaints on a pair of headphones I so recently gave much praise, but don't forget that these cost $40-$50. All forgivable when you remember the price. These headphones shine with house, jazz, pop, acoustic, most rnb or neo soul. They have great mids and listening to bass or bass guitar is a treat. For this price, I still highly recommend these headphones. They are not portable but if you don't have kids or a noisy house. These are great. 

Before I bought Superlux HD 668B
 
I am also owner of,
Creative S750D
Logitech Z5500D
Sony Muteki 7.4 Home Theater
Roccat Kave 5.1
Psyko 5.1
Audio Technica AD 400
Bose Quiet Comfort 2
 
and I must say, Superlux HD audio quality sound stage surpass all of my past audio gear except or comparable close to the Sony Muteki 7.4 quality.
 
Before i begin review, I suggest those out there that wanted to get a surround gaming headphones, 1 word of advice, they suck!!
 
In Roccat Kave 5.1, despite their awesome bass vibration driver, the sound quality distort painfully at high volume and clarity is like dog **** licking on paints colors. For my other speakers, you know z5500 sucks at bass badly and Creative S750 is broken from the start. My Bosecomfort 2 on the hand was just lacking on clarity compared to Superlux.
 
In the Superlux 668B HD audio, big difference can be spotted on the spot! First, it can go MAX volume in window and both me Auzentech Prelude Sound card!! WOW!!! With my roccat 5.1, I would have go deaf if i were to listen at max volume!!
 
 
Second, the sound effect is soo damn crystal clear that even turning on ******** filter found on creative cards would made you hear it all!!
 
blah blah blah....i can keep going on. but love it! later~
 
 
 

I didn't quite believe what I read when I heard all the hoo-haa about these headphones. I thought to myself, hey, when I have a spare thirty bucks lying around - maybe I'll try them out.
 
A friend happened to ask me what I'd recommend as a cheap set of cans, and knowing about the existence of these - I thought I'd try them first before telling him the usual 'lots of other people on the head-fi forums say these are great'.
 
Basically (as I realise has been said before) believe the hype! I was foolish not to trust you head-fi.
 
I let these burn in for a week back in December. I normally use a pair of DT990 Premium (600ohm). I also use a pair of DT1350's at work (great isolation) and I'm a fan of the RE-Zero/Audéo's when I use IEM's. The sound from this pair of 'cheap' headphones almost matches the quality of much pricier headphones, especially when driven by a nice amp - i'm using the iBasso D-Zero as my DAC of choice right now as it sounds very nice paired with this set of cans.
 
#Tested using:
- Audio Research DAC8 / iMac / iMod with D-zero
#Sound selection:
- After Dinner - Paradise Replica
- Andy Stott - Passed Me By
- Jenny Hval - Viscera
- The Rolling Stones - Beggars Banquet
- Charles Mingus - Ah Um (2 disc)
- Portico Quartet - Isla
- Claudio Abbado (Wiener Philharmoniker) - Beethoven Symphony No.9
- Nat King Cole - The Nat King Cole Story (Capitol Remaster)
- Demon Fuzz - Afreaka
 
Sound:
They are semi-open backed, so as expected, they leak sound terribly and have practically zero sound isolation. However, they do isolate against external noise, so you won't hear people talking etc, but they will hear you. It will annoy people if you're sharing close quarters and wanting to play your music loud (and I do play my music loud). That's not a problem at home for me - so I've been trying out a range of high quality live classical recordings, electronica and dance as well as reggae and more bass heavy noise rock.
 
These appear slightly dark and boomy in the bass end, but the detail is there. Otherwise they are very bright in the upper mid area (without sibilance), they provide the great instrumental separation that I expect from good semi-open backed cans as well as the wide soundstage and a feeling of distance between recorded objects (on well recorded sessions). The sound stage isn't quite as great as on my pair of HD650's or DT990's... no real surprise. However, it's worryingly close.
 
I tend to drift toward neutral/warm when it comes to headphone preference. The sound signature on these is pretty close to neutral... every so slightly warm. Another hit in my book.
 
Once you really, properly listen to these, if you have experience on very nice - much more expensive headphones... I guarantee you'll have a 'holy crap' moment. I didn't believe that I would - but I definitely did. I find it odd that some people dismiss them as 'cheap crap'. They may well be cheap - but I wouldn't describe these headphones as crap. Not by a long shot.
 
Build Quality:
This is the area where they suffer - but, it's not THAT bad. It's just your usual cheap plastic construction. They feel like a cheap plastic toy that you'd give to a child... I'm wondering how long the rubber cable connector will last, but otherwise - it's satisfactory. I didn't expect it to be great.
 
I do wonder whether the sound would be more open if I were to replace the stock p-leather earpads with AKG velour pads... I'll try, it's only £6! I might try opening them up more at the back too.
 
Comfort:
I'm a bit of a pin-head to be honest. I heard people complain about the DT1350 clamping down like a facehugger on the back of your head. I never experienced this issue - and I definitely don't with these. They are quite loose if anything but you can definitely tell that you're wearing them. There is no apparent method for adjustment - one size fits all. If you have a big noggin, then you might have an issue - otherwise I don't see it as a problem. A bit sweaty after extended use, due to the pleather pads. I'm going to replace those I think... I'm sure lots of other people did the same. 
I've scored them as 2.5 stars for comfort -which may be a little unfair - they aren't 'uncomfortable'. They just aren't outstanding in this area at all and could definitely be improved.
 
Overall:
I really like these headphones (if you haven't guessed that already) - basically, if you're ok with a very neutral sound and possibly a little fiddling with EQ to get some niggle out of the high end - you can't go wrong. There is simply nothing that I've heard at this price range to match them... All hail Superlux!

Amazing Headphones.
 
I 1st found out about these cans when I walked in on a new audio shop in our local mall. They had a lot of cans and IEMS available for audition so I listened to one. I was blown away with the detail and just about everything, there are also some Sennheisers there but these really stand out for me I couldn't put them down. My first thought was these must have costs more than those Senns but when I asked the salesman he told me it only costs around 40$. Wow! Really? So I researched about the brand and found out it was really praised very well here and other audio sites. Long story short, I bought 1 the next day.

The sound is nothing like great bang for the bucks read in the reviews on forums. It's rather cold, thin, dull .. On any genre, from DnB over Guitar Rock to Classical music. These earphones are no fun at all.

If I had to pin it down, I would say this:
The worst thing about these headphones is that they offer zero "stage" and so little "detail" that it doesn't make sense for to listen to any good music with them.

I'm not trying to be the "against" guy here, because as you can see, it has so many good reviews, but in comparison to my old Philips (which died just before I bought the Superlux), the 668B are just a huge disappointment in every regard.

It's like changing from a Ferrari to a Fiat - Somehow the same, but not really -.-

After a year with this amazing cans i think i can say a couple of things.
 
How the hell they can make this cans for this price?? China it's the answer...
 
Value:
 
This cans are amazing for only 20€, they do an unexpected sound quality for the price. It's not a Giant Killer but it's a Mini Giant Killer (MGK), i own a Sennhesier HD555 and -for sound quality- the HD668B are at the same level no doubt, but for 1/4 of the price. 
If you like the music and want to experiment audiophile sensations but haven't soo much money i can't imagine better 20€ on sound equipment. 
 
Audio Quality:
 
Taking appart the price and forgetting the price to loose the Hype i must to say that his quality sound it's good, at the same level of cans with my HD555. Differents sound signature but same quality level .
 
The very best sound of this cans cames when we burn in about 200-300 hours, recesed mid came more forward and don't miss it soo much, and the initial bright blows up a bit but don't dissapears. At his 56ohm and sensivity is not a requisite amplifier the HD668b to make it sound good but an amplifier make it push his best sound, resolution, instrumental separation, etc.
In other words they are more Mini Giant Killer with a good amplifier on the way.
 
It's supposed to be balanced cans for the B on HD668B but it seems to me it's not balanced flat, it's balanced on "V" like the Beyerdynamic DT990 -on the superlux website it's frequency response it's compared and it's very similar-, soo take in mind that, this cans aren't Flat at all.
 
This cans are very analitycal, very detailed with envolvent sounds and with a very good soundstage, all this make rediscover new things on music you use to listen; little sounds that wasn't before but appear with them, it's a good sensation rediscover your old music on it.
They are very transparet on the recording quality sound, if you find distorsion don't blame on cans, blame on bad recordings and mastering studios or the bad music quality music you heard. Most pepople says this cans are bright and i think it's beacause of it, if the recording it's bright the HD668b make you to know "screaming" to you
 
The bass its well extended and present, maybe a bit muted on the very low frequencys (20-50HZ) but much more present on middle low frequencys (50-150hz) and with a very funny punch on it. Many people will found it  short of bass but i think its the perfect quantity to feel it real and not overbass.
I found the punchy bass very very funy and enjoyable on it. But without amplification dont expect miracles... 
 
The mids are a bit recesed at first but after 200-300 hours it came a bit forward and you don't miss it anymore, unless you like very forward mids in that case you don't like it. They are very well balanced after the burn in, very detailed, with clarity and natural.
 
The highs are very very good for me -but i like crispy sounds!!-; some people found highs very very present on this cans and don't like it for this reason, it's a point to have very present on it. I think that the  bright highs dissapear a bit after the 200-300 hours of burn in but always be there.
 
The "timbre" it's not bad at all, is not the most realistic -my Sennhesier HD555 have a more crystalline "timbre"- but i like it soo much on cord instruments and female voices and acoustic concerts. Maybe not as realistic as my Senn but much more fun and enjoyable.
 
A good amplification cames to life many many things to this cans and make it a lot of better, don't miss this point. Not soo much ohms on the way but with his sensivity (98 db SPL) a good amplifier change many things.
 
Desing&Confort:
 
Nothing to say that you couldn't see on the photos. They are a copy of AKG on design and Audio Technica on headband pads. They are really light, lot of plastics every where, but well built and support hard treatment on it without broke it. Mines has fall down many times to the floor and still survive!!!
 
The pressure on the head maybe its a bit hard to support many time continuisly on the head and hurts but with time it take the form of your head and will bee more confortable, but it's there.
 
The most criticable thing on this cans it's the ugly earpads that would you sweat on summer like an idiot, and maybe Superlux would take the point for next models...
 
They have a cuple of cables (1m and 3m), one jack adaptor 3,5mm to 6,3mm and a clip to swich with no problem the cable to headphone that it's a new great idea rom Superlux and would must copy other brands.
 
Overall:
 
This it's a good cand, a very very good headphone for the price, i can't imagine a better 20€ expended on  sound equipment.