Cons: Without a dedicated head phone amp - just reversed from the pros.
This headphone could give you an excellent sound stage without high- piercing treble and thin bass with one condition - you need a dedicated amp for this one to shine.
Although this headphone stated about 56 ohms for each side, 112 in total and should be easy to drive with just any setting, it is not. I have tested with Asus Xonar Essence STX. At first, I used a low-gain in headphone amp setting and experiences all negatives everyone found in this headphone. However, after switching to a high gain amp setting, everything was changed for the much better.
This one is by far the best value headphones for its price if you have a dedicated headphone amp for it.
Cons: stock pads are awful, build quality isn't fantastic.
I have written a review in danish at the danish head-fi-forum, which is called Hoved-fi.dk, and I'll now do my best to translate it into english:
I have on a few occasions heard of Superlux, and that their headphones, despite being low cost, aren't the worst one can buy.
A few days ago, I had the opportunity to buy a pair of HD 668 B's for what equates to roughly 21.50$, including the cost of shipping and a pair of velour earpads.
Naturally, before recieving the headphones, I had seen quite a few written and video reviews of the HD 668 B, but since I do not seem to share sound preferences with a whole lot of reviewers, I am never quite sure what to expect from a headphone.
Finally: The arrival of the HD 668 B's! I removed the stock "leather" pads without even trying them with the headphones, as all of the reviewers mentioned that the stock pads were awful. The velour pads are very comfortable, and because the headphones weigh next to nothing, they are also comfortable for longer listening sessions.
The build quality regarding the rest of the headphone can best be described with the words: "You usually get what you pay for"
Except for the headband and the holders for the "wings" that rest on your head, the headphones are made of plastic. They dont squeak or rattle when handled, but apart from that, there aren't many more nice things to say about the build quality.
Not that they are going to fall apart with everyday use, but on the "nice-materials-scale", I'd give them a 2 out of 10 - because there at least is some metal included in the construction.
The headphones are sold with (I believe) a 10 foot and a 3 foot cable. I got mine secondhand, and only got the longer of the two cables.
The cable is rather thin, but is at least detachable, so if you happen to step over the cable, it should just come right off - if not, the cable can be replaced as described.
The 668 B's make use of what I'd describe as "wings", that rest off the top of your head, and prevents the headphones from sliding down. The concept is fine, but you might have to bend the wings (carefully!) a bit, in order to adjust the clamping pressure on your head.
I have owned a pair of Hifiman He-350, that I'd - before owning the 668 B's - describe as being bright. HD668 B is, however, even brighter, and a bit more aggressive.
If you'd like a bit more lowend, you can try adding more layers of foam in front of the drivers.
If you one day find yourself with 30$ you don't know what to do with, I'd recommend you try out the 668 B's - If my description of the sound seems like something you'd like.
I am not going to go more in-depth about the sound, as I do not consider myself to be experienced enough to properly describe other sound characteristics - and I do not want people to be mislead by improper descriptions
Pros: With Mods:
* Sound is clearer
* Bit Brighter
* Treble is tamed somewhat and wonderful
* Mids are brought forward
* Bass is punchy and not overpowering
* Lows are accurate and very responsive
* Great with all types of genres
* Detachable cable
Cons: Right out of the box With-Out Mods:
* Treble too hot and harsh
* Mids are lost over the treble
* Wiring not the best
* Clamping to much
First, off the Superlux HD-668 B are a great value for what you get. I recommend modding them for better listening sound and comfort.
Added electrical table inside the cups covering the holes. This lowers the sound stage but not too much and helps control the sound.
Removed paper inserts in the cups because not needed with 1st mod
Removed foam inserts. Clears up the sound, helps to tame the treble somewhat, and also, bringing the mids forward.
Resoldered the poorly done wires for better lasting connection.
Fixed the clamping by stretching the headphones out.
Testing: Equipment Used: SMSL sApII headphone amp running through an SMSL M2 USB DAC using Digital Output mode in Linux with PulseAudio. Method: I listen to a wide variety of genres from Jazz, Rock, Metal, Electronic, and Classical/Orchestra. So I tested a bunch of songs from each different genre and they all sounded great without anything missing from them.
Treble is way too hot and has a harsh sound. To fix this is to trim back the 4khz - 10khz rage in an equalizer but I have fixed this somewhat by modding these cans, but some EDM songs not all can have hot/harsh treble if mids/lows aren't playing at the same time.
Mids are not pronounced and are covered up by the harsh sounding Treble. This can be fixed with an equalizer or mods.
Bass is punchy and not overpowering that it will blast your head off.
Lows are not missing anything in their range. They sound accurate and are very responsive.
Vocals are very clear and natural.
Superlux HD-668 B is not the best build quality but at this price point, I wouldn't expect it to be. Its made of plastic but nothing is wrong with that. The stock earpads are cheap and uncomfortable. I recommend replacing them with a good quality pair of earpads. Also, the wiring inside is poorly done. The head pads are not bad and can be adjusted. They are lightweight so they can be worn for long periods of time.