I was in need of a decent pair of IEMs to wear on the trail for when I'm cycling, running and what not to use with my phone. Read all the reviews online praising these for the low price. Got them for around 12$ on GearBest so unless GB started shipping fakes, I'm pretty sure they're legit. Took the better part of a month to get them though.
 
Anyways, the packaging is impressive, you get a nice set of tips for them - I only found the mediums - which are on the headphones when you buy them, and the large ones to be usable. The other ones, S and XS do not seal for me at all and all the bass leaks out, I hear nothing below 500 Hz.
 
I prefer the M tips (and they do change the sound quite a bit so experiment with that). However I've found my experience with these phones to be not so in line with the reviews.
"Smooth treble, too much bass?" Hmm, found quite the opposite. When listening at the same volume as on my Superlux 668B, the treble kills my ears. It's not so much that the phones are overly bright, it's that there are what seems to be some really nasty high-Q resonances in the 2-4K range of up to 6 dB or so which I haven't even been able to isolate that well with a good VST EQ. Simply when certain sounds play, especially white noise sweeps in EDM music, some of these frequencies just go so much higher than the rest of the signal that it literally hurts my ears. I have to turn it down, but then at that point, everything is too quiet and the bass disappears even further.
 
Oh and about the bass, it's nice, tight, but it's not really deep enough to be immersive and to really hear the low end. Seems to roll off fast below 60 Hz or so. 60-150 Hz is OK and then the midrange dips quite significantly again, leaving things sounding distant and hollow, lacking depth. They're definitely not warm. Even my Superlux which is generally regarded as a mid-light set of headphones, brings sounds closer to the front than these.
 
So, for the price I don't think I can buy much better (though I have yet to try some of the KZ models), 12$ and I guess they're fairly good for the money, but not really 'giant killers' of any kind and for me they definitely didn't live up to the hype.
 
Would I still recommend them to someone? Probably, simply on the off chance that they're just not compatible with my ears. My brother doesn't seem to complain about them being shrill so I might hand them over to him.

As the saying in the title goes, this has never been truer than for these headphones.
Thankfully, Superlux sells sound quality, not an overhyped brand name. Can you really get great sound for $40? Oh yes, and it's right here.
 
I was recommended these headphones by a fellow forum member and after a day or two of investigation I decided I really liked what I read about them and figured if it was true, then these would be the best headphones I could buy on my really limited budget. So, I did.
 
Before I give any impressions, a small disclaimer: My previous headphones were Trust HS-6200 5.1 USB, and Trust Multi Function Headset 310. The most "hi-fi" component I have in my house is a set of Logitech Z-5500's. They run via coaxial, while everything else runs from the motherboard Realtek ALC889 codec (best Realtek codec, but still onboard.) So, I have not had much experience with quality components, but I know how to trust my ears. Hopefully, this will be enough to make a relatively accurate assessment of these headphones. Let's take it from the outside in.
 
Design: Well, the first thing that surprised me is that they are relatively small. I expected them to be a bit larger from the pictures. The next thing is, they are really light, weighing only at around 200 grams, which is good as it makes them easier to keep on the head for longer periods of time. The build is fairly sturdy and the plastic is of good quality, they look like they will last long. I'm not going to comment much about aesthetics, aside from the "Studio Monitor" labels being a bit tacky, but I generally like the way they look.
 
Comfort: A bit on the tight side. Causes my ears some discomfort after having them on for a while (upwards of 2 hours), but after a few minutes break it's good. I've read some people claim it made their ears sweat and heat up, I haven't had those problems but I don't normally sweat much anyway.
 
Accessories: With these headphones you get a 3m cable (for PC use) and a 1m cable (portable use) which you can exchange and even combine together. You also get a 3.5 (1/8") to 6.3 (1/4") mm jack adaptor, which is a nice feature, and a carrying pouch to, well, carry them around.
I liked the cable flexibility the most, I think it's a great idea.
 
Sound: And here we go, the most important part. I'll try to refrain from analyzing these headphones in the typical fashion here such as how the "highs, lows, mids, etc." sound as I don't think I'm familiar enough with the terms here but I will attempt to describe their overall sound signature with my limited experience, so here goes. What you play through them is what comes out. A bad recording will sound bad, a good one great. They are really transparent, simply "passing on" the sound without leaving a hint of presence of their own. And honestly, I like this. I want to hear my music the way it was recorded, intended to be heard. I don't want headphones to change my music. Sure, colored headphones may make it sound more "fun", but that's not the way the artist heard or made the track. Well, to each his own I guess. To continue: they reveal a lot of detail. A lot. Background hiss, noise, breathing, coughs from artists and stuff I have never heard before in my music. I have to play through everything again, to rediscover all those tiny details I missed out until now. The frequency response doesn't have many spikes, and it corresponds with what you can see on the manufacturer's website.
Soundstage, well, it's generally good. Certainly better than the closed-back headphones I own. These are only semi-open however. Sound isolation is still OK, I can hear myself typing and my noisy PC case, but when music plays it's hardly audible. To sum it up for the Superlux HD668B: Add nothing, reveal everything.
 
Oh, one more thing: the bass. I've seen a lot of people claim the bass isn't strong enough, while a few claimed the bass was good. And I believe I know why. It actually depends where you plug them in. If I plug them into my PC case's front port, the headphone out on the Z-5500, my cell phone or MP3 player, the bass is overwhelming, in fact there is more bass than there is in the 5.1 headphones that had a dedicated subwoofer inside, and it certainly does not sound natural. However, if I plug them into the rear ports on my motherboard where there is supposedly a headphone amp the bass tames down by around 80%.
 
EDIT: After a bit of longer listening, I've realised that it's not the amount of bass that changes. It's the amount of mids and highs. The thing is, the output ports on the back of the motherboard are assignable. If I set the jack to "speaker out" they give a line level signal, and the headphones sound substantially less clear and you have to turn the volume up from 35 to around 80; this gives the impression that the bass is louder - it's not, it's only that the signal is not strong enough to drive the mids and highs up to point. When switched to "headphone" setting, the headphone amplifier kicks in and the higher frequencies -really- jump up, leaving the bass behind at the "normal" level. This is why it seems it has less bass. So even though these headphones are only 56 Ohms, they certainly benefit from amping, and well at that. Line-level won't cut it.
 
Overall, I am extremely happy with them, will keep them around for a long time. My next purchase is going to be an Asus Xonar Essence ST, I can't wait to hear what they will do then. Well worth the money I paid for them and more, and would recommend them to anyone in this price range, for sure.