Pros: Cheap, good basic sound, cheap, decent build quality, cheap, includes carrying bag, cheap, self-adjusting headband and did I mention it's cheap ?
Cons: Harsh highs (solved by the filter mod), a bit tight clamping, all plastic (but makes it light) and not solid feeling.
I'm member on a forum for bassguitar players and since a few years the Superlux HD681 are the most spoken of headphones on there. Because of the price vs basic sound quality. After I bought the DT770 pro it seemed funny ordering this one on top, for comparisment and good for recording too.
Because I really dislike the one with the red rings I bought the one with silver rings, not realizing that it has a different sound. But it looked cooler, that's a lot to be said here...
Let's roll !
Okay, so what does one expect from €19,95 headphones ? They're made entirely out of plastic, but don't look too cheap. They have some thight clamping force and the self-adjusting system seemed to work fine, only not really smooth. But overall decent build headphones with easily removable earpads and even service friendly. The cord is thicker than the one on my AKG K271 so even there I don 't see any problem. It's a AKG clone, but Superlux gave it some own style-elements.
A self-adjusting system is always nice, but it does have a thight clamping force. I solved this by pulling it over a box and leave it like that for a day. Now the clamping force is normal for my head. With the AKG velours pads comfort didn't aprove, I acually prefer the stock pads, they have more clearance around my ears. Got no problem with them being sweaty too, allthough it has been extremely hot around here the last few weeks. The Superlux HD681 is quite light, which adds on comfort. Overall suitable for long term usage.
Sound quality (before filter mod) :
So, dare one speak of sound quality on €19,95 headphones ? At first I was disapointed... a lot ! Couldn't understand why all these guys were bragging about it on the bassguitar forum. I'll try to paint the picture:
Bass: The bass was very decent, nice punchy drumkick, bassguitar present in the mix. Not really deep bass, but well noticeable. It's more like a low-mid bass, somewhere around 80hz or so. But in metal (what I'm working on at the moment) the 80 hz region is very important. So I would call the bass sound "sufficient".
Mids: Mids where very clear from the beginning. The guitars really slammed me in the mixes I'd allready did with the DT770. But seems the Superlux puches mid foreward a bit. Cause when I lowered the volume of the guitars they became recessed in the mix. So I would call the mids a bit "over the top".
Highs: Here was where I could really hear this thing had only cost me €19,95 ! Too much highs ! Harsh highs ! Non-musical highs... really not good in this department. It sound like it has its own treble boost build in. So I definetly cal the highs "harsh".
Of course, since I have the B version, that's voiced like a K240, I have the "Balanced" version. Nothing balanced about the highs though...
But then I read on this forum and on Rock Grotto that these Superlux headphones started to sound better if they had some playtime. And I found the mod with the filters to take away the treble boost feel. I have been playing these headphones for days now and I really hear the highs getting a better sound. Still too much, but better sounding. A friend of mine, who's into electronics, is looking into the filter mod and I will get them in there for sure. If the highs soften this headphones simply have a very usable sound. So I will comment further on sound after the filters have been added.
EDIT 21st September 2013: a few days ago I've done the mod with the filter that softens the harsh highs. The Superlux are different headphones now ! Now they're really "balanced", even very close to my AKG K271. Incredible how $8 of components can chance cheap (sounding) headphones into expensive (sounding) ones.
Sound quality (after filter mod):
Bass: They are not bass-heavy headphones, but the bass is okay. It's not deep, more like a 80hz and up bassrespons. But it's compareable with the 7 times more expensive AKG. So don't expect punch in the basrespons, but it is very useable.
Mids: The installed filter takes care of the highs and in some amount the mids are also tempered. They're real sweet mids now, just as I like them on my AKG K271. Before the filter the mids were a bit over the top, puching vocals and guitars foreward. This has been solved beautifully by these filters. Now the mids are nicely balanced and dependable.
Highs: Allright ! Here we are... the difference in unbelieveable ! Gone are the harch highs, welcome to the new sweet, musical highs that suddely make these $25 headphones sound scary close to the 7 times as expensive AKG K271.
As far as I understand it, soundstage is all about stereo imaging and instrument placement. Well, that's not one of the strong points of these headphone. The sound sits a lot "inside the head" making it difficult to place the instruments. The stereo image is a bit rough, could be because of the forwarded mids and the harsh highs. But hey, what do you expect from €19,95 headphones that says "studio monitor". I cannot image one will use these for mixing, but I believe it would be a decent phone for guitar or bass recordings.
At this point it's hard to say because I 'm planning on the filter mod. But out of the box I think these headphones can satisfy many music-lovers. It's fairly neutral sounding, besides the overexaggerated highs, and many won 't even mind the highs. I read a lot of reviews where people say the HD681 can, with some mods, sound like $150 headphones, but I seriously doubt that. It is no match for the DT770 pro or the K271 studio. Not by a long run.
Conclusion after the filter mod:
These headphones were $25 and the filters have cost me about $8. This makes it a $33 headphone. After the filter mod the sound is truely balanced and really does have a "studio monitor" feel over it. It is definitly useable in the studio for recordings, allthough the open build will cause problems. Now I have to agree with all those who claim this Superlux HD sounds like a $150 HP after the filters are in place. At this moment it even is a match for my $200 AKG K271. Or it's at least surprisingly close.
After these filters I had to upgrade "Rating" from 3 stars to 4 and half stars and "Audio Quality" till max.
Here are some pictures of the B version with the AKG velours pads: