AKG K553 Pro Closed-Back Studio Headphones

Used it extensively for almost 5 months with my FiiO M11.

Trebles

• Detailed but not sibilant
• No sharp spikes in the region
• Rock tracks' treble fest won't be a problem most of the time
• Clear and airy trebles add dimension into the stage and imaging

Mids

• Well-bodied and balanced mids
• brings out the beautiful tones of piano tracks
• male and female vocals are both sounding full
• "hidden" mids in rock tracks are unearthed

Bass

• Above average tightness
• quantity is a little on the less side. Bassheads will not like the quantity.
• Sub bass is rumbly and present

Soundstage and imaging

• Wide soundstage for a closed back
• panning of instruments in well recorded orchestral tracks are precise
• sound is in front of you and not inside your head

Build and comfort

• Plastic and metal build feels sturdy and solid
• Pads are oil depots though
• Do not change the pads to velour and any open material as the bass will vanish
• Clamp is just right for my head
• cable is detachable but is not balanced out ready. You'll need to mod the 3 pin connector.

Hailed by Metal571 as the best headphones under $200, I have since discovered that his emphasis in headphones is heavily on frequency response. The frequency response of the AKG k553 mkII pro perfectly matches the Harman target, and as a result was very pleasing to Metal571 in particular. Tyll also praised them, despite their "zazzy" sound. These are a hidden gem. So who should buy these?
These were my first pair of decent headphones after the Sony mdr v55. They were my gateway to the audiophile hobby, and at the time i had a very low budget. Being so shallow-pocketed, I did a huge amount of research before any purchase. I could not afford the luxury of multiple pair of headphones for multiple genres. These are perfect!
First of all, lets get past the practical issues presented by the build.
BUILD:
1) I have an average head, and wear these on the first notch. These are not for small heads. My mother can't really wear them for example.
2) The cable is not detachable and is 3m in length. 'Nuff said. I modified mine without difficulty to 1.2m.
3) These are very big and industrial looking, so even after mod I dont wear them outside the house. I do often play these from an LG quad-dac equipped phone, which allows me freedom of movement about the house, but please stay inside with these. Hahaha! The upside is that they are very robust.
4) Though large, the cups are circular and shallow. This can make them uncomfortable for my average ears. It is tricky to find a fit where they dont rest right on your ears.
5) Speaking of fit, a good seal is absolutely essential to the sound. These sound completely different and possibly intolerable unless they are sealed properly.
SOUND: (!!!!!)
Great. Simply amazing. Better than so many popular headphones at this price. Complete absence of the typical flaws/problems with cans at this price. There is sub-bass. There is width and depth. They are non-fatuiging. They are as fun as the music, and pair well with any genre.
Amazing. Couldnt have made a better choice.
Compared to the AKG k550 which I also have own, the mid-bass boost is firstly noticeable, enjoyable, amd also welcome. It does no harm to any music that is not bass oriented, merely leveling the response. Do I prefer the k553? Maybe. I'm not a basshead. What I really appreciate however, is the removal of the 6kHz peak. Holy cow was that a pain. I sometimes couldnt even listen to speech recorded on a poor Mic.
Versus the Philips SHP9500, these have a singificantly smaller soundstage. However, separation and imaging are better. Possibly depth too. Less "3-blob". These have bass too, where the SHP are useless for any EDM/Pop. The stage is very surprising for a closed back. Compared to the popular hyperX cloud gaming headset, these are in another league. Better everything.
These make any cheap pair of headphones sound "whooshy", "whizzy", confused or just wrong. This is the only pair I know of that lacks any major flaws at the price-point. Comparing it against others in the same class, the flaws are fewer but ever present.
Need I say more? The only thing left to do is to compare them to far superior headphones. Against the HD800S for example, while the 800s are not as finally balanced, lacking bass and with slightly problematic highs, everything else is far superior. Its a huge jump, from cardboard cutout, to lifelike waxwork. From pencil sketch to photographic realism. There really is no compare. With the AKGs I have to focus on the music to hear it, but the Sennheisers display it so clearly it cant be missed. However, on anything cheaper, the qualities such as width, depth, tonal balance, resolve, plankton etc. are simply not there.
Thats where I believe this headphone stands. It is the perfect office headphone, isolating sound and being forgiving of poor audio sources, yet projecting a flattering image of almost anything. Strong recommendation.

I liked the sound of the drivers, but if I moved my head a bit, or bent down to look at something (like maybe a mixing console), one or both of the earcups now become a bit looser, and pull away from my ears, not a lot, but just enough to change the sound. If I push a tiny bit on the earcups, exerting more force against my ears, the headphones sound much better. I did not keep these. Once again my SONY 7506's are still my reference headphone. I am about to try some Beyerdynamic DT-770 Pro-80 headphones. It'll be interesting to see how those compare to the SONY 7506's.  

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.