Superlux HD 668B and HD 681 Headphones

A goodly amount of forum chatter has been focussed on these two very inexpensive Superlux headphones. (Superlux is a Taiwanese maker of professional audio gear, and is distributed in the U.S. by Avlex.) I thought it would be fun to have a listen and see if the headphone enthusiast community has stumble upon some giant killers.

(C'mon, how much can $30 really get you?)

The Superlux HD 668B and HD 681
Looking rather like an unwanted love child of an AKG and Audio Technica drunken trist, the Superlux HD 668B (~$30-$40) is about as unstylish as a headphone can get. The HD 681 (~$30-$40) is a bit spiffier looking with its red accents, but remains a utilitarian AKG look-alike headphone.

Build Quality and Accessories
I'm quite surprised at how durable these cans appear to be. Everything is cheap plastic, of course, but the implementation and use of materials seems quite well executed. The pleather pads are nicely stitched, and main parts are screwed together --- for the price, these are nicely built cans.

The HD 668B cord is replaceable, and uses a scheme I've not seen before: a very short (1") stub of a cable with 1/8" stereo plug on it comes out of the left earpiece. You then attach one of two included 1/8" stereo headphone extension cables --- the four foot cable for use with portable gear, and a ten foot cable for home and studio use. The HD 681 has a permanently attached eight foot cable terminated in an 1/8" plug. Both headphones come with a 1/8" to 1/4" adapter and fabric carry pouch.

Ergonomics, Comfort, and Isolation
Both headphones are full-size, circumaural (around the ear) type headphones. The earpads are thick, but a little stiffer than I like. Nonetheless, the earcup is quite large and my ears easily fit inside the cup without feeling cramped. Long listening sessions should be possible with little physical discomfort.

I typically feel the Audio Technica "wing" type headband pads are a bit insecure on my head. I didn't find this to be the case with the HD688B --- probably because they are quite light and the earpieces have a bit more range of motion than the AT headphones. Both headphones felt secure on my head.

Both headphones are touted as Semi-open designs and provided only modest attenuation. I found this a little odd as they are intended for studio use; typically I would expect cans of this type to be sealed. These have enough isolation for uses around the home, office, and dorm room, but will not isolate well enough for travel, commuting, and audio professional applications.

On to sound quality ...

Avlex Corporation (U.S. Distributor)
6655 Troost Avenue
Kansas City, MO 64131

Gatepc's picture

I love it when you review stuff like this, the weirder stuff. Thanks and keep it up very interesting read!

Cheesebaron's picture

You can replace the pads with AKG 242 velour pads, that gives a bit more comfort, at least on my HD 681.

Tyll Hertsens's picture
Thanks for the tip, mate.
saleemkhan's picture

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Esmalin's picture

Pretty spot on review on these budget monitors. I`ve been using 668-B (with velour pads) for a month now and have been extremely pleased. High are indeed on powerful side but I`m just enjoying music alot more since I got these. Low price and pretty robust and functional construction are good points as well.

Personally I feel that you get fair improvement on sound if you use amplifier on 668-B but it is not absolute requirement. 681 should be easier to drive if manifacturer specs are on spot.

There is also closed model of 668-B called 669 for those who need more isolation.

itsastickup's picture

I've worked out the equalisations for these cans. They sound pretty good. I've benchmarked against my ety HF5's, which are considered a bit bright. running off a rockboxed clip+ :

-2db 3400Hz q=0.6
-8db 5000Hz q=0.6 (probably due to ear canal resonance: so your ears may be different and you may find a higher q, ie. 1, helpful)
-3db 8400Hz q=0.8
-6db 12400Hz q=0.75

Finally you still need -7db or more on the treble tone control as while the above flattens out the spikes the treble is still overall higher than normal.

Tyll Hertsens's picture
itsastickup's picture

slight mistake the q for 8400Hz is 1.3 not 0.6.

vahan's picture

I'm going to buy one of them, I have classic ipod 80gb so which one sounds better on ipod without aplifier?

Lawk's picture

I hate my 668B. It's not high resolution IMO it is just bright and harsh, even EQ'd it doesn't sound right to me.

Frigo's picture

With my FiiO E07K, the following peak filter (Orfanidis type in Electri-Q) provides the best results:

-10dB @ 4800Hz, q=1/3 (BW=3.447 octaves)

Meshail's picture

Dear tyll

how are you i wish you are good :) ... i want to get a headphone for classical & full orchestra music ... sadly i can't afford the models i really want right now so i'm gonna pick somthing cheap right now so i wanna know which will perform better at listining to a full orchestra ... i want more details & separation & ofcourse the better sound quality .... so is it the superlux hd 681 or the sennheiser hd 201

thanks & BR

reindeer's picture

This review certainly put a downer on what I've read elsewhere on these phones (especially the first class goldenears ratings of different characteristics of the 668), but then I honestly didn't find the reviews on this site especially helpful or balanced in view of other headphones so far. For example, rough treble textures would make them potentially no worse than the Beyer 880, and if the 668 is as clear as goldenears says, it is even better for a quarter of the money. I also find the place of honour for the Philips Fidelio much exaggerated in view of its pros and very noticeable cons and I don't relate to saying the veil and colouration of the Sennheiser 600 somehow doesn't matter.
Nevertheless, now I don't know what to do, as always when looking for a better headphone...

donjoe's picture

Well the thing is many of the reviews you've read elsewhere were based on long-used or properly burned-in 668Bs. When I got mine new (or barely-used, as the previous owner disliked them and sold them quickly) I got the same impression in the above review: the highs were so harsh I couldn't stand them (unprofessional measurements with my smartphone later showed me it was primarily a 6-7 kHz "knife" stabbing me in the eardrum, plus a sibilant peak around 11k).

BUT... I gave the burn-in hypothesis a shot and played:
- 51 hours of pink noise
- 60-ish hours of music, pink noise and frequency sweeps (which I kept changing because I was so undecided as to what would be best)
- 80-ish hours of 20-20k frequency sweeps.

After the first two phases the harshness toned down somewhat, but they still sounded too aggressive and sibilant to listen to for any length of time, but after phase 3 (sweeps-only) all that changed substantially: now I could hear a reasonably flat and pleasant response with very little sibilance left and no more ear-stabbing going on. Yes, they remained bright, but in a way that you might call "detailed" or "revealing" rather than "harsh" or "fatiguing".

I wish Tyll had used these for his burn-in hypothesis testing, because there's a world of improvement to be made to these by burning them in, as opposed to top-brand already-high-quality ones that may be far less responsive to the intervention.

skris88's picture

Tyll, I'm 62 this year. I just bought this pair of HD668B headphones because I my most recent 'phones made me want something semi- or fully-open backed.

I immediately reached for my iPhone Treble Reduce EQ settings as per your comments and found the sound dull. I set it to Flat and it is much improved. I now listen to it with 2dB cut at 32Hz sloping down from 1kHz.

It shows your hearingand mine is very different.

I love the fact the bass on this is tighter (or at least much tighter than my previous open-backed headphones).

Still, thank you for pointing me in the direction of these cans.

Great sound, especially so for the $40 they cost me (on special)!