A quick background on my purchase: I have been looking to get a decent pair of earphones for on the go. Since I have some decent full-sized cans at home, I can't exactly deal with crappy-sounding earbuds.
 
I did not have a budget in mind, and was willing to spend upward to $200 for a nice pair of in-ears. However, I do not believe expensive = good sound, and was willing to try out a bunch of well-reviewed earphones in different price tiers. After reading an extensive number of reviews, I narrowed down my choices to the following: Xiaomi Piston 3, Yamaha EPH-100, and the Dunu DN-1000
 
Now, the Xiaomi Piston sets (both the Piston 2 and Piston 3) have popped up again and again as recommendations in IEM reviews, but unfortunately I was a bit skeptical because of their price ($20 according to most sites, though I found mine on GearBest for even cheaper - $12). Regardless, the Xiaomi I ordered ended up being the last one to arrive, so I tried the Yamaha and the Dunu first.

The Yamaha EPH-100 I received was a potential counterfeit, since it was an open-box item and has the pronounced grooves on the housing, and I simply don't think they sounded any good - enough to draw suspicion. So I will not include the Yamaha in my comparisons.
 
The Dunu DN-1000 ($160 brand new from Amazon) on the other hand sounded absolutely fantastic, and right off the bat I knew it was a keeper. The Xiaomi Piston 3 had a VERY tough job measuring up to the Dunu for sure - in fact I was quite sure I would give it a few minutes when it arrives, go "Meh..." and put them aside. No big loss for $12, right?
 
Boy, was I wrong.
 
The packaging is very tasteful and luxurious for this price - the acrylic carrying case with the silicone cord wrapper is very classy and good-looking. The accessories is barebone: 4 pairs of eartips, but that's frankly more than adequate at this price range (and due to the superb comfort level, you really don't need to mess around with the tips like you would on earphones with fit issues).
 
Materials and craftsmanship are all top-notch. The Piston 3 uses a lot of metal - and while the housing has more plastic than the Piston 2, I find the design to be better-looking (and reportedly the Piston 3 is far more comfortable). Plenty of earphones in the sub-$100 category feel more tacky and plasticy than this.
 
Of the three IEMs I tried, the Piston 3 is actually by far the most comfortable and easiest to fit. To be fair, it has the most shallow fit of the three, but it sits very snug in the ears without putting too much pressure. Superb ergonomics.
 
 
The Piston 3 is reportedly much more balanced than the Piston 2. I haven't heard the Piston 2, though the reviews on Headphonelist kind of gave the impression that Piston 3 may be relatively bass-light (just north of neutral). This was not the case at all: The Piston 3 actually has a LOT of bass (more so than I am used to; to be fair my full-sized cans are not bassy sets), and retains pretty good control over it considering the quantity. I would actually rate its bass quantity to be on-par with the Dunu DN-1000, although tightness and extension is not as good.
 
Mid-range and treble clarity is excellent; these are not muddy-sounding in the least. I simply cannot imagining getting a better sound for this kind of money.
 
Nit-picks? Sure, there are a few issues. My biggest gripe with the Piston 3 is there's too much lower-treble energy relative to the mids, which causes certain instruments to sound too sharp/metallic and unnatural. Depending on the recording, metallic instruments can sound a tad "splashy" while strings (particularly violins) can sound a bit screechy. I also noticed some unnatural artifacts in certain tracks (soundtrack from Gravity for example) that seems to be the result of peaks in the treble. All in all it's not bad, and only surfaces during certain recordings, but it's something worthy of note.
 
Mid-range is a recessed, especially evident when cross-comparing with the Dunu. Voices have real weight and presence on the Dunu, whereas they sound more distant and withdrawn on the Piston 3. It's not a dealbreaker for me, but if you like mid-centric headphones you may find Piston 3's V-shaped profile bothersome.
 
Bass extension on the Piston 3 is good but the emphasis here is definitely on the mid-bass (I tend to prefer headphones with sub-bass emphasis, as they tend to offer a clearer presentation). On tracks that have mostly mid-bass, the perceived bass quantity and quality between the Piston 3 and the Dunu are actually quite similar. But the moment the sub-bass comes in, the Dunu flexes its muscle while the Piston 3 takes a backseat. Bass tightness is more than adequate for this price range, clean with very fast decay. Only on the most challenging tracks does the Piston 3 struggle (Afro Celt Sound System - Big Cat: The Piston 3 clearly runs into trouble at the rapid-fire bass at 5:50, whereas the Dunu DN-1000 and AKG K553 renders this part with no issue).
 
But like I said, these are nitpicks considering the price. Xiaomi could be selling these for $50 and people would still be talking about them - let alone the $12 I paid for them.
 
Are they "giant killers"? Well, depends on how you look at it. The Piston 3 are excellent but if you have experienced good headphones, then they certainly won't replace the good sets you have. But for inexperienced people looking to be introduced to high-fidelity sound in their music, I can't think of a better place to start than the Piston 3 (the excellent packaging makes these excellent gifts for friends who are still using their crappy cellphone earphones).
 
In fact I am ordering another pair of these for a good friend right now.
 
The fact that I am keeping these after having heard the Dunu (over 10x more expensive) speaks volumes for the Piston 3.

I've been looking for a good pair of portables to complement my ATH-EM9d (which are nice, but they provide no isolation and they lack bass, which meant they aren't suitable for many genres or movie-watching). Ideally I wanted something I can travel with that would isolate the cabin noise on trains and airplanes. I already own several full-sized cans and have never enjoyed dragging those around when I travel, so I started looking into IEMs.
 
After reading an extensive number of reviews, I narrowed down my choices to the Xiaomi Piston 3, Yamaha EPH-100, and the Dunu DN-1000 (I know they each belong to very different price tiers, but I wanted to know how big the differences are in sound quality before deciding how much I actually want to spend, heh).
 
Well, the Xiaomi Piston 3 hasn't arrived yet so I can't offer a comparison, but between the Yamaha EPH-100 and the Dunu DN-1000, the Dunu easily won by a huge margin (sorry Yamaha, looks like I'll be returning you...) Below are my impressions.
 
Dunu threw in just about everything except the kitchen sink - frankly given the sound quality at the price I got it at ($160 brand new from Amazon), I would have been happy with half of the included accessories. There are eartips of all shapes and sizes, an accessory pouch, a hard carrying case, and two adapters (one for airline, which is perfect for what I need).
 
Craftsmanship on the Dunu appears to be excellent - the entire housing is metal and seems to be very solidly constructed. I did wish the cable were user-replaceable mainly because the housing seem difficult to disassemble and if anything goes wrong with the cable, I won't know what to do. But other than that, can't complain.
 
Comfort-wise, I found the foam tips to provide the best long-term comfort as well as the best seal. The housing is quite large and heavy for an IEM, and I found all the silicone tips to require the use of spacers to provide proper seal and comfort (and even then they don't seal as well, or are as comfortable, as the foam tips). The best silicone tip combination I found was the use of blue or red spacers coupled with the wide-bore single-flange (semi-transparent) black silicone tips.
 
Just absolutely breathtaking! These are the first BA-based IEM's I have tried, and I was just blown away by the detail and clarity present in the treble and mid-range. I had read some reviews saying that the BA drivers made the treble brittle and unpleasant, but I didn't find this to be the case. At least based on the materials I listen to, I didn't find the treble to be harsh or sibilant. There's just the right amount of sparkle without being offensive.
 
The bass is thunderous and goes down really deep, which is definitely a trait I like (I love sub-bass over mid-bass, as I am used to the AKG K550/K553). That said, there's just a little bit too much of it sometimes and I feel the bass could be a bit tighter (the K553 is about how I like my bass, and I do feel the bass is tighter on that). The texture of the bass on the DN-1000 is fairly fluid and dynamic, which is in stark contrast to the fast and crystalline texture of its BA-based mids and treble. The effect is most comparable to listening to speakers that have separate tweeter & subwoofer units, that's the best way I can describe it. It takes some getting used to, as I have never heard this quality in a headphone before.
 
This may be less of an issue when I am traveling, though, since as a general rule bass needs to be enhanced when there's background noise. I have a feeling I'll find the sound signature of the DN-1000 to be just perfect when I am on a train or airplane.
 
All in all, very happy with my purchase and looking forward to updating my impressions with further listening.

Update: Tyll Hertsens at InnerFidelity has expressed interest in doing a review of the K553. I was told to contact him in mid-October. I will be shipping him my K553 for lab measurements; look forward to seeing the results.
 
I've owned a pair of K550 for over two years now, and while I have grown quite fond of them, I was never fully happy with the way they sound. The treble does sound a bit unnatural - as noted by many professional reviewers - and both the bass and the mid-range could use a bit more body. The K553, it seems to me, is AKG's attempt at directly addressing these issues. I picked up a brand new pair of these for $120 on MassDrop, though many retail outlets are also selling these for $128 shipped.
 
I honestly cannot imagine a better headphone for these prices. Below are my impressions of the K553.
The K553 comes in a plain cardboard box that feels rather cheap, but then again, you only pay $120 for them. Some of the details could have been better though - for example the signal cable and stereo plug could have been tied down instead of being allowed to freely bounce around the box during transit. Even the $50 Superlux HD668b was better-packaged, in my opinion.
Packaging issues aside, the K553 is manufactured to the same quality standard as the K550. I read early reports about the earpads feeling "cheap" compared to the K550. That was actually my initial impression as well (the pleather felt harder and more rough, and the foam also feels harder), but after wearing them for a while, they quickly softened and now feel identical to those on the K550. Everything else seemed fine - I spotted no rough seams in the plastic bits, nothing felt loose or badly put together.
 
Retaining K550's exact designs means those who had comfort or fit issues with the K550 will likewise have them with the K553, so... possibly a problem for some.
 
Before I purchased the K553, I had read up on user reviews - some claimed they sounded identical to the K550, while others claimed they sounded very different. I was a bit skeptical about the claimed improvements, since AKG's official specs are identical to the K550, and they certainly look identical in the photos. But, for $120, I figured I could hear them myself.
 
Listening to the K553 yielded an immediate surprise - there are some very significant and tangible differences. Keep in mind I was skeptical about this to begin with, so I was fully expecting to hear identical, or at least very similar, sounds. I was not looking for differences to spot.
 
My immediate thought was that perhaps the new earpads were the cause, so I swapped them, and the results remained the same. I then went one step further in my investigation: I suspected the differences were caused by changes made to the driver enclosures, so I took both headphones apart, inspected for physical differences in the enclosures: I spotted absolutely none - no new padding or dampening materials that I can spot. (Also, just for the record, the inside of the K553 enclosures are both stamped with the words K550 Ear Cup Left/Right, indicating they are the exact same parts.)
 
Then I took yet another step. I de-soldered the drivers of both headphones, and swapped them (so my K550 is now sporting K553 drivers, and vice versa). And get this - the sound signatures got carried over with the drivers. So whatever tuning AKG did to the K553, it's in the drivers themselves. My final theory was that may be AKG used the K545 driver units in the K553 (and forgot to, uh, update the specs on their website... or something), since the K545 is reportedly a much more bassy set. However, the K545 drivers have significantly lower sensitivity rating than those used in the K550, so this can't be the case either (see list below for why).
 
Before I dig into my analysis, here's how I divide the frequency ranges:
 

1. Sub-Bass: 20-40Hz
2. Mid-Bass: 40-80Hz
3. Upper-Bass: 80-160Hz
4. Lower-Midrange: 160-320Hz
5. Mid-Midrange: 320Hz-1KHz
6. Upper-Midrange: 1-3KHz
7. Lower-Treble: 3-6KHz
8. Mid-Treble: 6-12KHz
9. Upper-Treble: 12-20KHz

 
Alright, so here's the list of differences I observed:
 

1. Based on my subjective listening, I estimate the K553 to be 2-3 dB louder than the K550 (despite the drivers having the same sensitivity rating on paper). This is interesting, especially considering that the new ear pads, being firmer, should have placed the drivers further away from my ears (I also tried pressing both pairs of headphones closer to my ears to eliminate the difference; the K553 remained louder).
2. The K553 is significantly more bassy, particularly in the mid-bass region (I tested this with EQ). The two headphones seem to be comparable in the sub-bass region (20-40Hz), meaning the K553 retains the excellent bass extension of the K550. The mid-bass region (40-80Hz) is what makes a headphone "thumpy", and this is where the K553 really deviates away from the K550: Based on my EQ tests (centered around 60Hz), the mid-bass is about 4dB louder on the K553. If you liked the way bass was handled on the K550, you may not like the changes to K553 - but in my opinion this was an improvement as I felt the K550's bass did lack body (in spite of the excellent sub-bass). The upper bass (80-160Hz) remains clean and appears comparable on both headphones.
3. The midrange on the K553 bears one distinction from the K550: The upper-midrange (around 1KHz) is more recessed. The effect is very noticeable in female vocals, which sounds much more forward on the K550. Based on my EQ tests, the difference is about 3dB (meaning if I lowered the 1KHz slider by 3dB while listening to the K550, the vocals would sound comparable to the K553 - not counting the differences in the treble, more on that later). The FR graph for the K550 from Innerfidelity does show a small peak in the 1KHz region; I suspect the curve for K553 may be more linear here. Whether or not this is a welcome change will depend on the listener - I personally think the K553 sounds more natural.
4. The treble is another area where the K553 really deviates away from the K550. My first impression of the K553 (aside from the significant bass boost) is that it sounds less "congested" in the lower-treble region (3-6KHz), and looking at the FR graph for K550, there is a peak at 6KHz. Lowering this region in the EQ by about 3dB on the K550 (in conjunction with the adjustment in the upper-midrange) produced a sound signature that, I feel, is similar to the K553. Additionally, I feel the K553 have less of a roll off in the upper treble (centered around 16KHz), and some textures that sound a bit indistinct on the K550 are more clearly heard on the K553. The mid-treble (centered around 8KHz), which affects metallic instruments, sounds comparable.
5. Lastly, sound imaging has been improved over the K550. The K553 does sound less "airy", but I feel whatever allowed the K550 to sound that way also hurt the accuracy of its imaging. The K553 addressed this and I can much better pinpoint the location of sound sources on the K553.

 
The overall sound of the K553 is just that much more pleasant and balanced to my ears. They are much more musical due to the improved treble presentation and added bass body, but still tonally neutral enough for analytical listening and sound editing work. Aside from the minor issue of the bass sounding a tad loose at times, IMO the K553 successfully addressed all the shortcomings of the K550 while retaining all of its merits.
 
Seriously, at $120, the K553 is an absolute steal. In this price range the only competitor I can think of would be the ATH-M50 (you can't even buy the M50x for this price), and the K553 easily outperforms the M50/M50x in every category, and has better material & construction to boot. I cannot imagine another closed headphone for under $200 that sounds this good.

Two years ago, when I was looking to upgrade my aging ATH-A9X, I came across the AKG K550 and the ATH-A900X, both then newly-released, with several head-fiers reporting that they are tonally-similar headphones. Unable to decide which one to get, I bought both to do a comparison. I ended up keeping the K550 for myself and giving the A900X to my wife (who still uses it and loves it).
 
Below are my thoughts regarding how these two cans compare.
 

1. The A900X isn't a bad-looking headphone, but lacks K550's elegance. That said, comfort level is excellent and I in fact prefer it over the K550 in this department. The AT "winged" headband design makes putting them on and taking them off a breeze, and the angled drivers do not press against my ears even after my prolonged use (whereas the K550 causes discomfort).
2. One particular thing another reviewer complained about was the "poor quality" of the wings on the A900X. I looked into this issue, and did not personally find this to be true (relative to previous models). Below are my observations:
   1. On the old model A9X/7X/5X, the wings only pivot in one direction (let's call it the Y-axis), which is up and down.
   2. On the A900, AT implemented the "3D Wings" which pivot in two directions (X- and Y-). The way they achieved this is by making the wings themselves into a 2-piece design - there's an "outer rim" that pivots around the Y-axis (like the old wings), and an "inner piece" that pivots back and forth (X-axis).  This is actually a fairly intricate design and I imagine, harder to manufacture.
   3. On the A900X, AT simplified the "3D Wings" to ease manufacturing process while still retain pivots in both directions. The wings themselves are now back to a 1-piece design and pivots up and down (like the old wings on A9X), but the T-shaped joint where the wings are clipped onto the arms now pivots back and forth (in the older models, this joint is fixed). The joint on the new system makes the wings feel loose, giving the appearance of flimsiness, but having owned this headphone for two years I can attest that the construction quality on the wings are solid.
3. Material quality on the A900X is decent but not great. It's a step up from the A900 (which had the cheapest pleather possible and several plastic bits just look like sub-$100 headphones), but it's not at the same level as its older cousin, the A9X (which had supple protein leather earpads and wings). The earpads on the A900X is a durable-looking pleather that feels a bit on the hard side, and the wings remain fabric-covered like on the A900.
4. One nitpick: The stereo plug on the A900X is the exact same one AT has been using since the mid-90's (starting with the old ATH-AX series). It might have looked ok in the 90's, but looks a bit gaudy by today's more understated aesthetics.

 

1. The K550 is simply one of the most tastefully-designed headphone I've seen. The construction, materials, and appearance are all superb (my photos don't do them justice).
2. Comfort level is good but there are some nitpicks here... The earpads could be a bit deeper. The top of my ears do press against the drivers because the foam used in the earpads are extremely soft. The earcups are a bit stiff when it comes to pivoting, so they may not conform to the shape of your head without manual adjustment. The clamping force of the headband feels a bit loose, especially if you have small heads (and this is a headphone that already has sealing issues)
3. The plastic used for the signal cord, while fairly high-quality, is still more prone to tangle and deform in comparison to Audio-Technica's fabric-wrapped cords, which retain their shape better. I personally prefer AT's implementation.
4. One material nitpick... The headband padding is pasted onto the headband using basically a double-sided tape. Unfortunately the adhesive becomes a black goop as it ages and, in my case, actually started oozing out from the headband and making a mess on whatever surface I leave the headphone on. I ended up tearing out the padding, cleaned off all the adhesive, then glued it back using a glue gun.

 
 
Several Head-Fiers have claimed that the A900X and K550 are tonally similar, which was the reason I was interested in these two cans to begin with. They turned out to be very different-sounding cans, heh.

1. Treble: The A900X has a fairly clear and resolving treble. It appears to be tuned to offer sparkle without being offensive or sibilant (there's a dip at 7K which, I suspect, was intentionally introduced to reduce sibilance). Extension is absolutely brilliant, going full up to 20KHz. The only complaint I have is that it's noticeably grainy-sounding compared to the K550, whose treble is simply silky-smooth in texture.
2. Mid-Range: The A900X's mid-range is thicker, fuller, and more engaging than the K550. It is definitely a more engaging presentation (more "musical" if you will), but clarity suffers a bit here. The K550 in comparison is more clean-sounding.
3. Bass: The bass is my biggest gripe with the A900X - there's quite a bit of mid-bass bloat and the control isn't particularly tight. Bass extension isn't very good either - the rolloff starts at 50Hz, which means there's not much sub-bass compared to the excellent extension of the K550. Without any earpad mod, the A900X has a bit of a consumer sound to its lower end (I personally found that swapping the pads for the oval-shaped ones from the A1000X helps dial the bass down a bit)
4. Soundstage: The A900X has a very wide sound stage, likely owing to its excellently-resolving treble. Imaging is likewise excellent - I feel this is one area where it has a definite upper hand against the K550, whose soundstage - while large - feels a bit indistinct.

 
 

1. Treble: The treble is a bit of a problem area for the K550. Many users have complained about it being "peaky" or "sibilant". I don't find this to be the case, though the lower-treble is definitely too forward, causing the slightly unnatural treble presentation noted by many reviewers (a problem compounded by the thin-sounding mid-range. Both issues were addressed in the K553). I also wish there were less roll-off in the higher octaves, as the K550 could benefit from better extension (it's rolled off from 1.5KHz onward). Complaints aside, clarity is good and treble texture is superb - there is absolutely no grain on the K550.
2. Mid-Range: The mid-range on the K550 has excellent clarity, which I really love. However it is sometimes dominated by the lower-treble, which as I mentioned, is too forward. Additionally it could use some additional body - the overall presentation does sound a bit bright & thin.
3. Bass: The bass on K550 has excellent tightness and extension, however it could likewise benefit from some additional body. I personally do find K550's bass to be thin-sounding due to the lack of mid-bass. There's ample amount of sub-bass and upper-bass, but the mid-bass is intentionally recessed. A 2-3dB boost in the mid-bass would provide a more balanced bass presentation (exactly what the K553 did).
4. Soundstage: The K550 is well-known for its spacious soundstage, and I do agree it feels very wide and airy. However, I feel the imaging is a bit fuzzy and indistinct. Watching movies and playing games, it's much easier to tell where a sound is coming from on the A900X.

 
The A900X and K550 are both good headphones with distinct personalities. Neither are perfect, though. I would say the A900X is the more balanced-sounding of the two and more versatile when it comes to musical genres and other usage (games & movies).
 
The K550 offers better clarity and may be more desirable for analytical listening and editing tasks, but it's not as musical as the A900X and many will find its treble presentation to be problematic.

Two years ago, when I was looking to upgrade my aging ATH-A9X, I came across the AKG K550 and the ATH-A900X, both then newly-released, with several head-fiers reporting that they are tonally-similar headphones. Unable to decide which one to get, I bought both to do a comparison. I ended up keeping the K550 for myself and giving the A900X to my wife (who still uses it and loves it).
 
Below are my thoughts regarding how these two cans compare.
 

1. The A900X isn't a bad-looking headphone, but lacks K550's elegance. That said, comfort level is excellent and I in fact prefer it over the K550 in this department. The AT "winged" headband design makes putting them on and taking them off a breeze, and the angled drivers do not press against my ears even after my prolonged use (whereas the K550 causes discomfort).
2. One particular thing another reviewer complained about was the "poor quality" of the wings on the A900X. I looked into this issue, and did not personally find this to be true (relative to previous models). Below are my observations:
   1. On the old model A9X/7X/5X, the wings only pivot in one direction (let's call it the Y-axis), which is up and down.
   2. On the A900, AT implemented the "3D Wings" which pivot in two directions (X- and Y-). The way they achieved this is by making the wings themselves into a 2-piece design - there's an "outer rim" that pivots around the Y-axis (like the old wings), and an "inner piece" that pivots back and forth (X-axis).  This is actually a fairly intricate design and I imagine, harder to manufacture.
   3. On the A900X, AT simplified the "3D Wings" to ease manufacturing process while still retain pivots in both directions. The wings themselves are now back to a 1-piece design and pivots up and down (like the old wings on A9X), but the T-shaped joint where the wings are clipped onto the arms now pivots back and forth (in the older models, this joint is fixed). The joint on the new system makes the wings feel loose, giving the appearance of flimsiness, but having owned this headphone for two years I can attest that the construction quality on the wings are solid.
3. Material quality on the A900X is decent but not great. It's a step up from the A900 (which had the cheapest pleather possible and several plastic bits just look like sub-$100 headphones), but it's not at the same level as its older cousin, the A9X (which had supple protein leather earpads and wings). The earpads on the A900X is a durable-looking pleather that feels a bit on the hard side, and the wings remain fabric-covered like on the A900.
4. One nitpick: The stereo plug on the A900X is the exact same one AT has been using since the mid-90's (starting with the old ATH-AX series). It might have looked ok in the 90's, but looks a bit gaudy by today's more understated aesthetics.

 

1. The K550 is simply one of the most tastefully-designed headphone I've seen. The construction, materials, and appearance are all superb (my photos don't do them justice).
2. Comfort level is good but there are some nitpicks here... The earpads could be a bit deeper. The top of my ears do press against the drivers because the foam used in the earpads are extremely soft. The earcups are a bit stiff when it comes to pivoting, so they may not conform to the shape of your head without manual adjustment. The clamping force of the headband feels a bit loose, especially if you have small heads (and this is a headphone that already has sealing issues)
3. The plastic used for the signal cord, while fairly high-quality, is still more prone to tangle and deform in comparison to Audio-Technica's fabric-wrapped cords, which retain their shape better. I personally prefer AT's implementation.
4. One material nitpick... The headband padding is pasted onto the headband using basically a double-sided tape. Unfortunately the adhesive becomes a black goop as it ages and, in my case, actually started oozing out from the headband and making a mess on whatever surface I leave the headphone on. I ended up tearing out the padding, cleaned off all the adhesive, then glued it back using a glue gun.

 
 
Several Head-Fiers have claimed that the A900X and K550 are tonally similar, which was the reason I was interested in these two cans to begin with. They turned out to be very different-sounding cans, heh.

1. Treble: The A900X has a fairly clear and resolving treble. It appears to be tuned to offer sparkle without being offensive or sibilant (there's a dip at 7K which, I suspect, was intentionally introduced to reduce sibilance). Extension is absolutely brilliant, going full up to 20KHz. The only complaint I have is that it's noticeably grainy-sounding compared to the K550, whose treble is simply silky-smooth in texture.
2. Mid-Range: The A900X's mid-range is thicker, fuller, and more engaging than the K550. It is definitely a more engaging presentation (more "musical" if you will), but clarity suffers a bit here. The K550 in comparison is more clean-sounding.
3. Bass: The bass is my biggest gripe with the A900X - there's quite a bit of mid-bass bloat and the control isn't particularly tight. Bass extension isn't very good either - the rolloff starts at 50Hz, which means there's not much sub-bass compared to the excellent extension of the K550. Without any earpad mod, the A900X has a bit of a consumer sound to its lower end (I personally found that swapping the pads for the oval-shaped ones from the A1000X helps dial the bass down a bit)
4. Soundstage: The A900X has a very wide sound stage, likely owing to its excellently-resolving treble. Imaging is likewise excellent - I feel this is one area where it has a definite upper hand against the K550, whose soundstage - while large - feels a bit indistinct.

 
 

1. Treble: The treble is a bit of a problem area for the K550. Many users have complained about it being "peaky" or "sibilant". I don't find this to be the case, though the lower-treble is definitely too forward, causing the slightly unnatural treble presentation noted by many reviewers (a problem compounded by the thin-sounding mid-range. Both issues were addressed in the K553). I also wish there were less roll-off in the higher octaves, as the K550 could benefit from better extension (it's rolled off from 1.5KHz onward). Complaints aside, clarity is good and treble texture is superb - there is absolutely no grain on the K550.
2. Mid-Range: The mid-range on the K550 has excellent clarity, which I really love. However it is sometimes dominated by the lower-treble, which as I mentioned, is too forward. Additionally it could use some additional body - the overall presentation does sound a bit bright & thin.
3. Bass: The bass on K550 has excellent tightness and extension, however it could likewise benefit from some additional body. I personally do find K550's bass to be thin-sounding due to the lack of mid-bass. There's ample amount of sub-bass and upper-bass, but the mid-bass is intentionally recessed. A 2-3dB boost in the mid-bass would provide a more balanced bass presentation (exactly what the K553 did).
4. Soundstage: The K550 is well-known for its spacious soundstage, and I do agree it feels very wide and airy. However, I feel the imaging is a bit fuzzy and indistinct. Watching movies and playing games, it's much easier to tell where a sound is coming from on the A900X.

 
The A900X and K550 are both good headphones with distinct personalities. Neither are perfect, though. I would say the A900X is the more balanced-sounding of the two and more versatile when it comes to musical genres and other usage (games & movies).
 
The K550 offers better clarity and may be more desirable for analytical listening and editing tasks, but it's not as musical as the A900X and many will find its treble presentation to be problematic.

The ATH-EM9d is an elusive model that was never sold in the United States - I picked these up in Taiwan during a trip to Taiwan in 2008. Production had already ceased at the time of purchase, with the new ATH-EMx00 series replacing the old line.
 
Even though the ATH-EM9d was being replaced by the ATH-EM700, the older model remained more expensive than the new one (the old EM9d was $190, while the EM700 was $150 brand new). I asked the shop owner (who is a long-time audiophile himself, and participated actively on several headphone forums) what he thought, and he said quite simply: "The new ones are junk. AT cut corners in materials all over the place."
 
One thing that was easily noticeable was the difference in the plastic used on the cords. The EM9d has the same kind of high-quality tangle-free plastic used on expensive headphones, while the kind used on the EM700 feels like the ones used on budget earbuds. There's also a lot more metal on the housing of the EM9d, whereas the EM700 uses a lot more plastic. I would say the older model does indeed seem much higher quality in both the materials and construction.
 
 
I did some brief listening of both, and the conclusion was easily arrived at... The EM9d trashed the EM700. The EM9d has much better extension and clarity, and the tonality is much more balanced. The EM700 was mostly mid-centric with relatively poor extension and sounded very muddy in comparison.
 
The packaging of the EM9d is the same as the rest of the Audio-Technica's clip-on line - very understated but classy. They come with a carrying pouch and an extension cord.
As you can clearly see, the EM9d are very sharp-looking headphones. Construction quality is on-par with the EW9. It uses the same grade of cord and the same earclips (which were redesigned on the EM700, and were not as comfortable). Comfort level is nothing short of excellent - I've worn these to sleep many times; you simply forget they are even there.
 
 
Audio-Technica is the only headphone manufacturer that makes high-end clip-on type headphones, so I read up on both the ATH-EW9 and the ATH-EM9d extensively before I went down to the shop. The EW9 is popularly referred to as the "Queen of Female Vocals" for clip-ons in the Taiwanese audiophile circles, while the EM9d reportedly was the "King of Neutrality".
 
I now own both the EW9 and the EM9d, and can confirm that the reviews I read were accurate. The EM9d is indeed very neutral; tonal balance is nothing short of excellent. The EW9, while indeed great for vocals with its thick, sweet mid-range, is only suitable for some types of music and lends too much coloration to the music for my taste.
 
It's worth mentioning that the drivers on the EM9d are titanium-plated, which likely contributes to its excellent clarity and treble performance.

Also note that it's a fully open-backed headphone (you can actually see the driver through the holes on the back of the housing). As such, the EM9d offers absolutely no isolation - which makes it suitable for certain situations where awareness of one's surrounding is desired (such as walking around on foot), but not so much for others (riding in a noisy subway train).
 
Treble: The treble on the EM9d offers excellent clarity and extends very well, but is otherwise quite smooth and unoffensive. It's not very sparkly and it's not for trebleheads, but I personally really like it. Sibilance is never an issue with these.
 
Mid-Range: The mid-range is very clear and just slightly north of neutral, but still in balanced territory. This is not the signature AT house sound, but IMO it's for the best. Instruments have very natural timbre, and listening to classical pieces on these will put a smile on your face.
 
Bass: For fully open-backed clip-ons, the bass on the EM9d is actually quite ok. It extends decently well and packs just enough punch to lend classical instruments proper heft (and the bass is very controlled and tight). Quantitatively, though, it is definitely on the light side and will not play well with bass-heavy genres.
 
Sound Stage: The sound stage on the EM9d is very open and airy, which is not surprising given its open-backed nature. The out-of-head feel of the sound and the lack of isolation often lends the strange sensation that you are carrying around an invisible stereo system while walking about.
 
If for any reason you want to invest in a good pair of clip-ons, you should try hard to find yourself a pair of ATH-EM9d. These are my absolute favorite in the category. For $190 though, there are better-sounding headphones outside of the clip-on category to be had - many good IEM's or over-the-ear portables are in this price range or below. So I am knocking this one down in the value department a bit.

I purchased these for my wife two years ago. She's always liked the warm sound of my ATH-A9X, so for portable use I got her the ATH-EW9, which reportedly has a very sweet, warm mid-range.
 
The packaging is the same as other high-end Audio Technica clip-ons, which is to say I find them elegant and classy.
The headphones themselves are simply gorgeous. The Hokkaido cherry wood housing are perfectly finished and the 35mm stereo plug is elegantly shaped and endowed with the letter "ATH-EW9 JAPAN" printed in gold.
 
The included accessories aren't as luxurious as the headphones themselves, which was a little bit of a let-down. The carrying pouch is the same one that used by the lower-end models (EM7, EM9d, EM700, etc.), and the netting used on the inside is a bit on the rough side - I worry about it scratching the delicate wood housing (though so far it seems to have been fine).
 
The included extension cable is also the same one used by lower-end models - I wouldn't complain about it if the EW9 used the same kind of 35mm plug as on the other units, but they don't. As the result, the contrast in aesthetics is rather stark when the EW9 is plugged into the extension cable.
 
Comfort
All Audio-Technica clip-on headphones are extremely comfortable in my opinion. They use a very unique type of earclip that's self-adjusting and doesn't put pressure on the ears, and the earpads are very thick and plush. I often forget that I am wearing them.
 
I actually have several gripes about the way the EW9 sounds, especially considering its price (about $200 retail, I think) as AT's flagship clip-on. It has a very thick and sweet mid-range, which is fine for those who likes this type of signature. However, I find the overall tonality to be peaky and problematic, particularly in the lower-treble region (seems to have a peak somewhere in the 4-8KHz region). There may possibly be some ringing issue, since the EW9 uses a closed-back design. In comparison, its cheaper cousin the EM9d (which I own, and much prefer) uses aluminum housing that's fully open-backed, and does not exhibit this symptom (the drivers on the two units are the same).
 
Treble: The treble extension should technically be the same as the EM9d, but subjectively it doesn't feel as good due to the mid-range being so dominant. The aforementioned lower-treble issue sometimes exhibits itself as sibilance, and other times as overly energetic "screechyness" (in string instruments for example). For vocals, this headphone is great - but instrument timbre simply isn't as natural as the EM9d.
 
Mid-Range: The mid-range is thick, warm, and very forward. Old-school AT fans may like this quality.
 
Bass: The bass has decent tightness and extension, though like the EM9d it is on the light side quantitatively.
 
Sound Stage: The sound stage on the EW9 sounds less open and more congested relative to the EM9d, both due to the treble issue and the closed-back design.
 
The ATH-EW9 is a very beautiful clip-on that's well-suited for certain types of music. But its high price and the uneven tonality limits its versatility - if you can find its cheaper cousin, the EM9d, I personally recommend going for that instead.

If you have been to Taiwan, you likely have seen one of these inside a CD store. It is one of the most widely-used headphones for CD listening stations there.

It was in fact my first exposure to "hi-fidelity" sound - when I was a teenager, I remember being completely blown away by these phones!
They can still be found for less than $30, which IMO makes them very competitive against the Superlux HD668b.
 
Materials & Craftsmanship:

The packaging is pretty barebone, though you do get a 1/4" adapter.
 
Materials feel cheap, obviously, but you get what you paid for $30. The LH-036 does have one feature I really like: The cups are connected to the headband via a ball joint, which pivots very easily for a good fit. Unfortunately the screw that affixes the earcups to the joint have the tendency to get a bit loose after a while, and each time this happens I have to open up the housing to tighten them (the joints also get squeaky if these aren't tightened).

 
The earpads are made of pretty cheap pleather, but they are very easily removable and serviceable.

 
 
Comfort
 
I don't find the LH-036 to be comfortable due to my ear size - the earpad opening is on the small side and not very deep. Clamping force is decent though, and the headband is actually very well-padded.
 
Audio Quality
The LH-036 sports large 50mm drivers, and the sound quality is actually very good for its price.
 
Technical Specifications:

1. Driver: φ50mm Neodymium
2. Impedance 32Ω
3. Frequency Response: 5-25,000Hz
4. Maximum Output: 100mW

 
Treble: The treble is my biggest complaint with the LH-036. It is very sharp and bitey - a problem I seem to also have with the Superlux HD668b. This is an extremely sibilant headphone and will require a good amount of EQing in order to sound pleasant. That said, detail and clarity is decent, though not quite as good as the HD668b.
 
Mid-Range: The mid-range is actually pretty good (when the treble is behaving). The LH-036 by default has a V-shaped presentation, but the mid-range clarity is decent and I would say have a slightly warm tilt.
 
Bass: With a good amp these headphones actually put out a decent bass with good extension and tightness. I actually think the extension is better on these than the HD668b.
 
Sound Stage: The sound stage is actually pretty ok. It's comparable to the HD668b, though imaging isn't as good (due to treble clarity not being on-par).
 
Conclusion
The Gamma LH-036 has been around for over two decades now - it's actually held up pretty well considering its age and price range. If you are in the market for some budget head gear and don't mind EQing for good results, this should definitely be on your list.

I bought these after reading all the rave reviews on Headfonia and Head-Fi... here are my impressions of them.
 
I think any criticism concerning materials or craftsmanship of the HD668b is nitpick considering its price of $50 (easily found for less) - I personally haven't seen headphones in this price range that are this well built.
 
It's obvious that Superlux took elements from both AKG and Audio Technica designs. The way the earcups pivot is very nicely implemented and conforms easily to the shape of the head. As for the Audio Technica-styled "wings", I've been a long-time fan of it and prefer them to traditional headband design, so that's a plus for me. Add these on top of the two sets of detachable cords, a 1/4 in adapter, a carrying pouch, and an anti-yank clip... I am honestly quite impressed considering the 668b's price.
 
The packaging is simple but elegant; a very clean and professional presentation. The cords are carefully wrapped to prevent movement during shipping.
Construction is very sturdy. No rough seams in the plastic and nothing squeaks or rattles. I personally find the comfort level to be excellent as well; the wings provide just the right amount of down force and clamping force is just right. The pleather used on the earpads are above-average quality and are fairly soft without the stickiness of the cheaper pleather types.
 
Audio Quality
This is where I have a bit of mixed feelings about the HD668b... perhaps because I had too high of an expectation from all the rave reviews. Since so many calls it a "giant killer", I was expecting to be absolutely blown away, and I wasn't.
 
 
 
Treble: These headphones were extremely bright and harsh-sounding. It's strange that the review on Headfonia claimed the treble was excellent - granted, there's a lot of detail and when it behaves, the treble is quite sparkly. But as you can see in the FR graph there is a very sharp and pronounced peak between 5-6KHz, which is THE area that causes sibilance (overall the entire treble region is just way too pronounced to sound natural). I am not sure why Superlux tuned this headphone to accentuate this particular area, but I agree with Tyll's (from InnerFidelity) assessment on this one... it's like listening to a good headphone through razor blades.
 
Mid-Range: The quality of the mid-range is good, though a bit recessed. I think in spite of the issues with treble, the 668b's drivers are quite resolving and the mid-range does carry good clarity. It's just unfortunate that it tends to be drawn out by the distractingly sharp highs.
 
Bass: Contrary to the Headfonia review, I don't feel the bass is particular tight or controlled on the 668b, and bass extension leaves a lot to be desired (as you can see in the FR graph, the bass starts rolling off at 60Hz, and I certainly don't feel much sub-bass from these cans).
 
Sound Stage: The sound stage for the HD668b is quite spacious, likely owing to its detailed treble, clear mid-range, and its semi-open nature.
 
Instrument Separation: The HD668b performs well here; the drivers' good resolution allows the details in the treble and mids to be heard clearly. Orchestral music is properly layered and instruments are easy to pick out.
 
Isolation: Isolation on the HD668b is passable - not any better than the cheap $30 full-sized cans my wife had before this, but not bad considering its semi-open nature.  It should be fine for private use in homes or for sound work at a quiet studio. Do be aware that HD668b has moderate sound leakage, however - and may annoy people around you in libraries and whatnot.
 
The Superlux HD668 are a good pair of headphones when seen in the context of its price range. Design and construction are superb, as is comfort. Its audio quality is a mixed bag, and if this really is the only entry-level headphone you can afford, then be advised you will need significant EQ to make it sound pleasant.  Then again, for $50, I think the HD668b is still a good deal as long as you don't mind having to EQ them.  Personally though, I would save up a bit and invest in something in the ~$100 price range for a proper introduction into the audiophile world. First-gen Sennheiser Momentum, AKG K553, Audio Technica ATH-M50, or a used pair of NAD Viso HP50 are all excellent headphones that can be had for less than $150.

I am the fortunate owner of a fairly rare pair of headphone: The Audio Technica ATH-A9X. It is the precursor to the highly popular and successful ATH-A900, and I feel they deserve a proper review (since so few people own them outside of Asia).
 
The Audio-Technica ATH-A9X was part of the second-generation "Art Monitor" headphone series that surfaced during the late-90's (it was produced between 1997-2002), alongside its siblings the A5X and A7X. It was preceded by the first-generation ATH-A9 (introduced in 1994) and succeded by the ATH-A900.  I do not own a ATH-A900, though I do own the the newest incarnation in the series - the ATH-A900X, and I'll be happy to do a brief comparison to show you how this popular headphone series has progressed and how it has stayed the same.  
 
The old ATH-AXX series was never sold in the United States. I purchased it during a trip to Taiwan in 2001. It is a very unique-looking and eye-catching headphone, and one would probably love it or hate it. That said, it is undeniable that the material and construction quality are very high - in fact I find it superior to both the ATH-A900 and the A900X in this regard.
As you can see, the cups are made of ultra-polished aluminum alloy. They look very slick, though fingerprints stick very easily.
 
The earpads on the ATH-A9X were very high-quality protein leather. It was soft, supple, and non-sticky (it breathes better than the kind used on the AKG K550), which made me really sad when I saw the kind of cheap pleather Audio-Technica chose to ship the ATH-A900 with. The A900X uses better-quality pleather than the A900, but still a farcry from what the A9X had. 
 
Like many of the enthusiast-grade Audio-Technica headphones, the ATH-A9X came with the famous "wing-support" system, and sits very comfortably on the head. This is in spite of their weight - at 350g, the A9X is pretty hefty for a dynamic headphone. However, the A9X has superior clamping force and the wings exert better downward pressure than the A900 and A900X (whose wings feel flimsy in comparison). They do not slip down and press against the top of the ears as its successors do. 
 
Several other traits of the A9X that are worth noting:

1. The plastic parts on the A9X are not monotone, but an elegant "metallic" brown (it has shiny metallic flakes in the material). It's subtle, but very elegant and tastefully implemented.
2. The cord is wrapped in tangle-free fabric, which is a silky brown color that complements the plastic frame. It looks a lot better than the simple black cords on the A900 and A900X, in my opinion.
3. The padding on the "wings" are also encased in high-quality pleather, as opposed to the simple fabric covers on the A900 and A900X.  This is a small but very nice stylistic touch in my opinion, as the wings complement the earpads very well when the headphones are not in use, and the whole thing just looks more elegant in comparison to its younger cousins.

 
The A9X has what - to my understanding - is called the "old school" Audio Technica sound. Intoxicatingly thick and warm in the mids, with rolled-off treble and bass. Here are its technical specifications, as provided by Audio Technica's Japanese website.
 
Technical Specification:

1. Mirror-polished, high-strength aluminum alloy housing.
2. Special coating completely absorbs unwanted vibrations and provides superior isolation.
3. Employs same φ53mm high-quality drivers from flagship model A10ANV.
4. Frequency Response: 5 - 30,000Hz
5. Sensitivity: 103dB/mW
6. Maximum Output: 2,000mW
7. P.A.T. anti-resonance mechanism.
8. High-quality cloth-wrapped PCOCC signal cord.
9. Specially-formulated pleather earpads.

 
*According to the specification sheet, the aluminum housing, the A10ANV-class drivers, the PCOCC signal cord, and the "special" pleather earpads are all unique to the A9X (not shared by the A7X and A5X).
 
Treble: The treble presentation on the ATH-A9X is rolled off and laid-back. The younger A900X is noticeably sparklier and more resolving, but depending on your preferences they can be more fatiguing. The A9X is very good for relaxed listening.
 
Mid-Range: The mid-range is A9X's strong suite (if you like the AT house sound). It is warm, thick, and forward. Vocals sound very sweet and full-bodied, and instruments (particularly wind and string) are intimate and inviting. I find the A9X to be excellent for smaller, more intimate pieces (small or solo performances). It lacks the resolution and expansive sound stage of its younger cousin to properly render complex orchestral pieces. The A900X, in comparison, sounds significantly cleaner and more neutral.
 
Bass: The A9X has an adequate amount of upper and mid bass to give proper presence to most instruments, and when present, it is decently controlled. However, the bass is rolled off quite early and there isn't much sub-bass that I can hear. Quantitatively the A9X is on the bass-light side, and isn't suitable for modern genres.
 
Sound Stage: The A9X has a curiously small soundstage (possibly the smallest I've ever heard in a headphone) - singers literally sound like they are signing into your ears. This works well for some pieces but not for others. It's an interesting quality and I wonder why AT tuned them this way. If I have one big gripe about the A9X, this would be it.
 
 
The ATH-A9X is a unique-looking headphone with a sound signature that old school Audio Technica fans enjoyed. Its younger cousins - the A900 and A900X have been progressing more and more toward being tonally balanced and neutral, so the likes of the A9X will likely fade away. That said, it is a small piece in AT's history that I will gladly hold onto.