Superlux HD-668 B

Introduction
The Superlux HD 668b where my first “non gamer” headphones as I always wanted to step up my audio gear and at the time (2020) it was the best over ear headphone I could afford.

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First Impressions (2020)
My last “gamer” headphones were the Steelseries Arctis 3. Both headphones feature a V-shaped signature where the bass and treble are a little bit boosted. However, when I switched from the SteelSeries to the Superlux, I instantly noticed that the sound opened. This is because in the Arctis 3, the mids seemed so lost beneath the rest of the frequencies that any voice or instrument in this range sounded lacking in body. Unfortunately, I sold the Arctis 3 several years ago, so I cannot make a direct comparison, but trust me, the improvement was significant.

Unboxing, Build and Comfort
For $35, the unboxing experience is very good. The headphones come in a decent cardboard box and come with a good variety of accessories: 2 cables (a 1 and 3 meters long), a 3.5mm to 6.35mm adapter and a carrying bag.

The build is mainly based on plastic except for the metal headband. Despite this, they feel like solid headphones that won't break from a few falls to the floor. Also, this amount of plastic makes them extremely lightweight, which is a plus if they are going to be worn for several hours. Clearly, this build is similar to several AKG models, and the headband is very similar to the renowned Audio Technica R70x. The earcup and headband cushions are made of pleather.

A particular thing about the 668b is a 3.5mm connector hanging from the left earcup to connect the headphones cable. Many people mention that this is a clear weak point in the construction and can break at any time. In my 4/5 years of use (not continuous but regular), they have not suffered any problems in this area, but I thought it was good to mention it so it is taken into account.

Comfortwise, this is the worst aspect of these headphones objectively. If you are a person who is used to the low clamping force headphones that float on your head, you will have a bad time with this pair. One piece of good news is that after two weeks of use and letting them rest with the headband open in some box or support, the clamping loosens considerably.


The earpads are also a problematic point for these headphones. They are very shallow, so it is very likely that the ears will touch the fabric covering the driver. However, according to what I searched (but have not yet tried), the earpads compatible with AKG K240 can fit in the 668b earcups, relieving the discomfort that the pleather and shallow earpads may cause.

Frequency response description

Credits: DIY-Audio-Heaven

• V shaped sound signature but sounds well balanced with bass notes not bleeding into other frequencies.
• Boosted mid bass but with good control avoiding interference with midrange sounds.
• Neutral midrange which makes female and male vocals sound natural and articulate.
• Boosted highs that are sibilant most of the times (problematic for mid and higher volume level listeners). However, they provide great clarity.
• Great extension in the treble giving a sense of "air" and spaciousness in music.

Subjective sound description


Bass
There is an early sub-bass roll-off, so these headphones do not extend that well in that range. However, there is a good amount of mid bass, it has punch shown on sounds like drums and on EDM song basslines. In "Vivere" in particular, the large number of instruments in the song can be heard clearly, with a very pleasant bass guitar which is always present behind the vocals without interfering.

"7th Dimension" (Koan Sound) has good bass rumble. The good quantity and quality of bass highlights electronic music, giving it a "fun" character. The 668b handles passages with a wide variety of synthetic sounds very well.

Mids
"Luck Be a Lady" (Sinatra live at Carnage Hall), his voice is immaculate and it seems like you are in the same theater listening him sing. The rest of the instruments sound well separated from each other and with a high level of detail.

With classical and melodic music, the voices and instruments sound organic and with a hint of forwardness. This also shows a well controlled bass execution that does not muddy the mids.

The midrange frequencies in general have a character approaching neutral, accentuating a bit in the upper midrange registers. Vocals in general are presented with great naturalness and have good clarity and presence in their reproduction thanks to the slight elevation between 1.5 to 2.5 kHz.

Treble
Sibilance is very noticeable in "Come rain or come shine" (Sinatra live at Carnage Hall) when the trumpets and cymbals sound together. This also happens in "Teach me tonight."

"Black Magic" (Slayer live) the cymbals at the beginning of the song are piercing at medium and high volumes. The lead singer has good focus sounding clear and prominent.

"No retreat" (Destructo) the bass is again well-presented, and the bells at 1:52 are quite sharp and overly bright, even at what are considered low volumes.

"S" sounds in "Strangers by nature" (Adele) have an exaggerated character.

Soundstage & imaging
Being a semi-open design, these headphones allow for better sense of spaciousness than IEMs or closed-back headphones. Its soundstage is not huge but it does expand a bit around the head. More wide than tall, but with good depth.

For the price, the imaging and separation that the 668b offers are incredible. Instruments can be differentiated from each other with clarity, their location and the distance between them on the stage can be perceived. There is also excellent articulation between voices and instruments.

I always test these two items with "Rime of the Ancient Mariner" (Live at Long Beach Arena). It's spectacular at minute 1:20 how you can tell with these headphones that the bassist and one of the two guitars are on the right side of the stage and the other guitar is a little to the left with the singer at the center. I can't always capture this detail, and the Superlux surprised me for the better.

Also in "Hydrogen" (M.O.O.N.), a song where the left to right movement of the bass notes is excellent, it covers the three important positions as it should (left-center-right).

Personal note
Its resolving character can become fatiguing at higher volumes and for genres that have many string instruments (rock or classical music with violins).

Conclusion
At the beginning of this review, it might sound like these headphones have more cons than pros. Ultimately, as someone who reviews audio products, I have to be as objective as possible, and yes, their comfort will leave something to be desired for some individuals (I don't mention it in the review, but it's not my case). Setting that aspect aside, the price to performance offered by the 668b is one of the best that can be found for over-ear headphones under $50: spectacular resolution, punchy yet well-controlled bass, organic-sounding vocals and instruments. If you're not afraid of treble or listen at low to moderate volumes, I am 100% recommending these Superlux headphones for budget-conscious audio enthusiasts.

Link to my review and measurement index thread where one can also find a full review overview, more information about myself as well as my general-ish audio and review manifesto: https://www.head-fi.org/threads/956208/

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I only give full stars. My ranking/scoring system does not necessarily follow the norm and is about as follows:

5 stars: The product is very good and received the "highly recommended" award from me.

4 stars: The product is very good and received the "recommended" award from me.

3 stars: The product is good/very good, but not outstanding/special enough to get any of my two awards. ["Thumbs Up"]

2 stars: The product is only about average or even somewhat below that and somewhat flawed/flawed in some areas. [neither "Thumbs Up" nor "Thumbs Down"]

1 star: The product is bad/severely flawed to outright bad. ["Thumbs Down"]

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Superlux HD668B


Source:

Review sample.


Miscellaneous:

Pretty inexpensive.

Unlike my Superlux HD681 that came packed in a cheap see-through plastic packaging, the 668B arrived in a proper packaging.

Included are a 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 have adopted design elements from several AKG and Audio Technica headphones.

The plastic used on the headphones 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 the case is 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:

I have the shorter (1 m) of the two extension cables attached.

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 oriented tuning wherefore voices sound natural and realistic – something that is especially nice to hear on headphones this inexpensive.
As the bass and highs are elevated, though, the midrange is perceptively 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 to my ears, 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 areas, 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, although undeniably tuned more towards the “fun” side.

Resolution:

Very decent – even more so considering how little these headphone cost.

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.

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 as 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.

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Comparisons:

Superlux HD681:

The HD668B sound bassier to me.
Deep bass extension on my HD861 is minimally better by ca. 3 Hz, but not much and only audible when performing sine sweeps.
The HD681 are brighter, leaner (and therefore less realistic) in the mids.
The same goes for the treble where the HD681 are brighter and peakier – out of the two, the HD668B are definitely the better-tuned headphones.

The HD681s’ 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 (but most likely only because of their tuning).

The two headphones’ soundstages are nearly identical to my ears, with the HD681s’ 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 my Fostex being a bit less full in the root, however below 100 Hz, the TH-X00 continue to climb further and further, and start to roll off much lower than the Superlux that are already really good in this regard, wherefore they have got considerably more sub- and midbass quantity than the cheaper headphones, with an overall more sub-bass-driven sound signature. Due to this more sub-bass-driven signature, they are the even more engaging and fun sounding headphones in the lowest registers.
The Fostex’ upper mids are more in the background, but not subdued.
The upper middle highs are clearly brighter on the Superlux, whereas the TH-X00 are tuned brighter in the starting super treble.
Out of the two, the Fostex’ highs sound more realistic and natural.

In terms of resolution, the Fostex are ahead, but the gap towards the Superlux is not as gigantic as one may thing. Not at all, in fact, as the latter still perform very reasonably when compared to the former that are ultimately however superior by a good bit in about every aspect regarding resolution.
Therefore, the Fostex’ bass rendering is cleaner, tighter, faster, better controlled as well as better layered; in the mids, they are more layered and detailed as well as refined sounding, which also applies to the highs.

The soundstage size is comparable with the TH-X00s’ appearing overall just a bit larger in terms of spatial width and depth.
In terms of imaging, though, the soundstage is cleaner and better focused on the Fostex, with superior instrument separation, a better portrayal of “emptiness” around tonal elements, and an overall more authentic imaginary room. Directly compared, the Fostex’ soundstage also collapses less when fast and busy music tracks are played, even though the Superlux do a good job at this as well.




Conclusion:

Recommended.

Inexpensive, well-tuned v-shaped fun sounding headphones with good technical performance and even midrange response.


Photos:

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.