@Redcarmoose I'd say 300 hours is the amount to get the last 10 percent of burn in, just like any other K7. Yes. Personally I found the K7XX to start sounding right after about 100-150 hours. With little burn in the treble is brittle and sibilant, and the midrange sounds sucked out and highly recessed. 

@cs098 The K545 definitely is a good choice for a great sounding portable overall AKG that doesn't require a dedicated system other than a smartphone or decent MP3 player.

Well-written, helpful review. If I have the K7XXs, the LCD-3s and the speakers all playing at the same time on my Schiit Ragnarok, the K7XXs will be the quietest. Yeah, these things like power. But they are very nice for $200.

Nice review. Pls do the comparison with the HD 650. I got them, too, so I'm really interrested on how they stack up against each other.

 A friend recently purchased ak712 after borrowing and listening to my old(over 5 years old) k701.
  I have probably well over a thousand hours of platy time on my old Austrian made k 701s.
He commented that he found my old k 701s to be more open at the top than his new k 712s. Probably  some of that is break in time. But I did hear what he was talking about. One thing about the old  k701 and probably why so many people criticize the 701 for is the need for a big beefy amp to power them properly. In fact you will probably have a tough time finding any conventional dedicated headphone amp including some really high powered ones to really grasp the k 701 and get the beast from them. I have found my amp in the form of a vintage monster receiver circa late 1970s. My concept 16.5 powers the  k701 like no dedicated headphone amp that I have heard with them . One look the  power supply on this beast speaks a thousand words. The dual transformers and well endowed power supply supplies the necessary muscle to really show what the k 701s can do. You I am sure have never heard bass on the K 701s like they do with the concept receiver.
  I have come to appreciate the k 701s and their remarkable abilities but it has been a long and arduous journey that most people would not have had the patience to endure.
   The  k701s were truly a statement of resolution.

Fiio E12 Works fine with the AKG K7XX. I don't know any really good sealed headphones from AKG (K550 and K271 are quite okay). And again some guys believing in the magical burn-in rainbow-unicorn-phenomenon. Right now i'm listening to my K7XX for over a month (nearly 4 hours a day) and i can't approve that the sound-signature has changed. And yes, i'm using 2-3 different headphones a day, so a change in one of them will be noticeable to me. The K7XX is a fine headphone, but the K601 will be my favorite AKG for quite awhile

Yes please do comparison K7XX with HD650...Thx

Would love to have a review of hd 650 vs these cans

Thanks for the review, but there are a few issues I find troubling. First of all it's alleged power hungriness is really not explained by it's flat impedance curve, if anything that should be a boon to an amplifier. The other is that you recommend amps that costs several times more than the HP in review, to me that's an automatic knock especially at this price level to spend that much to make this HP sound it's best. That's like saying you need a more expensive screen than the new front projector one just bought to get it's best.Of course this isn't your fault per se you just reporting your experiences, but I would have a hard time to recommend a product that needs more expenditure 2-3 times or more than the product to deliver it's best. AKG should really come up with a driver that is more efficient while retaining it's qualities that most people who like their sound care for.This can sounds like just another variation on the same "theme" AKG been composing for years,if not decades.

@LajostheHun You have brought up some very important points. I consider the K7XX fidelity-wise to be a 400-600 dollar tier headphone along the lines of the Beyer DT990 600 ohm, HD600, and HD650 for mid-fi prices similar to the HD598, which doesn't need a dedicated amp. The differences fidelity-wise between the HD598 and K7XX are night and day. The K7XX just has better engineered transducers and better fidelity. HD598 hits excursion and distortion levels far sooner. The K7XX's sibling, the K712, retails at an MSRP of 600 dollars, but since AKG prices vary wildly, the target of what level of gear for them tends to go all over the place. At 700 dollars you would think the Woo WA6, but if it goes for 200-300 dollars then think Objective 2 or Schiit Asgard 2. Because of that it's deceiving as logic says you buy gear based on how expensive your headphone is. However AKGs are counterintuitive as they scale noticeably better with more expensive gear, and their sound varies much more than the HD650 and HD600 on different systems. AKGs tend to not be the headphone for novices due to how system dependent they are. Often they can be a false economy with their competitively lower prices than Senns of equal fidelity, leading to people thinking they don't need as good a setup. I will go into this in my comparison video. If in doubt go with the Objective 2 as it will get the job done if not sound that last 15 percent exquisite or bring a lot of scalability out of the K7XX. 

amp matching is pretty straight forward, I think.
 
K700 series has a tendency to sound bright and thin if not used with right amp. since I cant enjoy these traits, they are difficult to amp.
 
Senn hd650 on other hand can vary from neutral to warm. I am ok with both cases. thus easy to amp as long as it can provide juice.
 
although I must say both hps are designed with different demographic in mind, akg caters pro audio, no guarantee which hp out they will be plugged into. while senn is geared towards audiophiles who will take time to build up setup. this approach pretty much thrives on our tendency to do careful system matching and invest time and effort to maximise potential.

How do you think these will fair when paired up with the FiiO e10k? (currently what I have)

@Kung-Fi The FiiO E10K should be decent for it, but FiiOs tend to not sound that dynamic with AKGs. 

Hey everyone, I uploaded a comparison between the HD650 and K7XX. Here it is:
 
http://www.head-fi.org/t/755497/sennheiser-hd650-vs-akg-k7xx

Hi, great review and information! Thanks for share! Did you try K7XX or any other K/Q/7xx series with the GeekOut 720 ? Is it appropriate for driving this HP or do you have any idea about its synergy with GeekOuts (450, 720, 1000)?

Great review, wondering what would be better match for jazz HD650 or KXX

@Baycode I didn't try them with that amp unfortunately. I was using entry level amps such as the Hifiman EF2A, Maverick Audio A1 and Audioengine D1. I only procured the Lyr 2 around the holidays in December, 2014. So I'm unable to comment on its performance with the GeekOuts. But it likes the same types of systems as its K7 siblings, so if there is a GeekOut that you've tried with another K7 and really enjoyed the synergy, the K7XX will also work well with that same amp.  Sorry that I am not able to comment too much here, as I've just used entry to now medium level hybrid amps, and am only going on word of mouth for other systems. 

@Johnlist Well let me ask you this: do you listen to jazz primarily as an analytical thing, or more for the musicality? Because both do jazz well, but the K7XX is more analytical at jazz and if you prefer to listen to jazz more for the technicality of it, the K7XX will likely be your better choice. If you listen to more jazz fusion and soul-style jazz, the HD650 with its warmer bass and mids will likely be a better choice. 

I'm getting a pair of these and dont have an amp I don't know much about amps though help would be great my source is just my galaxy S5 under $130 can go up to $150

@MilkyShakes I would go for the Schiit Audio Vali for an amplifier.