This & That:
Pretty inexpensive.
Unlike my Superlux HD681 that came packed in a cheap see-through plastic thingie, the 668B came in a proper packaging.
Included are the storage bag (feels quite cheap, but it's much better than nothing at this price point) that I already know from my HD668B as well as a similar 3.5 to 6.3 mm adapter, but in addition, there are also two cables and a clip that secures/locks the cable joint. I'm using the shorter 1 m cable.
It's obvious that the HD668B has "adopted" design elements from several AKG and Audio Technica headphones.
The plastic used on the headphone feels quite cheap but rather sturdy.
Proper strain relief on the cable and good flexibility. Cable attached to the left ear cup, which is the industry standard. I like the clip that secures/locks the extension cable in place.
Cable extension is a standard 3.5 mm TRS plug, so any regular headphone extension cable could be used in theory.
Cable microphonics are fairly low, which is nice.
Comfort is decent but not great.
The pleather ear pads are rather shallow but it's not as bad as on my Fostex T50RP Mk3.
The headband size is self-adjusting but the comfort or pressure distribution aren't great due to the split design.
Clamping force is on the higher side.
There is a bit of passive noise isolation, but not to the degree of most fully closed-back over-ear headphones.
Sound:
Usually, I'm using the HD668B with low impedance sources.
I have the shorter (1 m) of the two extension cables attached.
For what it is worth, I have got hair around my ears.
Tonality:
V-shaped with elevated mid- and upper bass ass well as upper middle and upper treble.
The midrange is definitely nicely tuned and follows a flat, diffuse-field target tuning wherefore voices sound natural and realistic - something that is especially nice to hear on a headphone this inexpensive.
As the bass and highs are elevated, though, the midrange is ultimately pushed further into the background of the mix.
The lows stay nicely out of the mids and don't start to climb before about 550 Hz; they then reach their climax somewhere around 100 Hz with an elevation of around 8 dB of what would be neutral, with a subjectively perceived strong, bassy impact. Level stays there down to 60 Hz; below that, the bass starts to roll off. Therefore, the midbass and upper bass are the most elevated, however the sub-bass isn't lacking at all and definitely present with similar quantity as the central mids, however probably not fully down to the very lowest registers where it is perhaps a bit below the mids' level.
The upper middle and upper highs as well as super treble are then elevated, with surprisingly high evenness wherefore the highs are bright but fairly (but not fully) realistic.
- - -
So yeah, a fun, v-shaped sounding headphone with a recessed but tonally correct midrange.
Resolution:
Very decent - even more so considering how little this headphone costs.
Pretty clean sounding bass that is only a bit on the softer side. Details are good, but not the most separated (sounds a bit blunt), despite being fairly tight and fast.
Decent midrange resolution and speech intelligibility - nothing sounds grainy here.
Treble resolution is good, but fast attacks could be rendered a bit cleaner.
- - -
So yeah, much better than expected for the price, and generally really respectable, good performance. In short, there are just no real technical flaws when it comes to resolution.
Soundstage:
On the smaller to average side with almost just as much spatial depth as width.
Reaches about from the left from the right ear cup and about to where my eyes are located.
Imaging and separation aren't s clean as on some of my more expensive headphones, but the imaging is anything but blurry and remains decently precise and distinguishable even when more complex music is played.
- - - - - - - - -
Compared to my:
Superlux HD681:
The HD668B sounds bassier to me.
Deep bass extension on the HD861 is minimally better by ca. 3 Hz, but not much and only audible when performing sine sweeps.
The HD681 is brighter, leaner in the mids.
The same goes for the treble where the HD681 is brighter and peakier - out of the two, the HD668B is definitely the better-tuned headphone.
The HD681's bass sounds a bit cleaner and tighter in comparison.
Both are similarly resolving in the mids and highs, with the HD861 appearing airier in comparison (only because its tuning).
The two headphones' soundstages are nearly identical to my ears, with the HD681's being perhaps just a tiny bit wider.
Fostex x Massdrop TH-X00 Mahogany:
Way different price league, but several similarities.
Both sound v-shaped.
The bass boost starts about similarly on both headphones until 100 Hz, with the Fostex being a bit less full in the root, however below 100 Hz, the TH-X00 continues to climb further and further, and starts to roll off much lower than the Superlux that is already really good in this regard, wherefore is has got considerably more sub- and midbass, with an overall more sub-bass-driven sound signature. Due to this more sub-bass-driven signature, it is the even more engaging and fun sounding headphone in the lowest registers.
The Fostex's upper mids are more in the background, but not subdued.
The upper middle highs are clearly brighter on the Superlux, whereas the TH-X00 is brighter in the starting super treble.
Out of the two, the Fostex's highs sound more realistic and natural.
In terms of resolution, the Fostex is ahead, but it doesn't totally smash the Superlux. Not at all, in fact, as the latter still performs very reasonably when compared to the former that is superior by a good bit in about every aspect regarding resolution.
Therefore, the Fostex's bass rendering is cleaner, tighter, faster, better controlled as well as better layered; in the mids, its more layered and detailed as well as refined sounding as well, which also applies to the highs.
The soundstage size is comparable with the TH-X00's appearing overall just a bit larger in terms of spatial width and depth.
The imaging is however cleaner and better focused on the Fostex, with superior instrument separation, a better portrayal of "emptiness" around tonal elements, and the overall more authentic imaginary room. Directly compared, it also collapses less when used with fast and busy music tracks, even though the Superlux does a good job at this as well, even more so at its considerably lower price point.
Conclusion:
Inexpensive, well-tuned v-shaped fun headphone with good technical performance.