Well here is my summary of what I remember and posted over time on another forum.
Tried multiple headphones in store twice and then these at home: BD DT770pro80, Senn HD569, HD599, 4x AKG K712 and 1x K702.
BD DT770pro80, bass for days, treble hot, no mids, no comfort, terrible build and design, return, pass, plays good but terribly V shaped, skull cracking clamping force with shallow pads
Senn HD569, comfortable if the pads are deep enough for you otherwise the hard hinge protrusion is painful a lot, sound wise don't even bother it's poor
HD599, boomy bass aroudn 200Hz no sub bass extension, no high treble, sounding narrow response wise as a result, high bass, low treble and nothing below and above that... shallow pads = hard hinge protrusion = pain, my old closed cheap Senn plays better than HD599 with better extended treble and overall sounding balanced unlike this modern typical Sennheiser coloration disliked by me where Senn prefers high bass boost in 100-200Hz, shouty borderline painful mids and cut off treble, guess Senn went to hell over the years thanks to hype and moving production to China and trying to please younger new audiences
HD600 would be the first I would even consider bothering from now on with Sennheiser and I still preferred Q701 in direct comparison, again shallow pads and narrow soundstage, good but not that good to deserve all the crazy praise
1st AKG K712, bought new received open box = return, sounded "OK" except I think it was sibilant with not enough bass as it should have? 36k batch, creaked too I believe, return obviously, not gonna stand for open box when ordering new, seemed legit when verified with AKG distributor who even told me when they sold it to the seller
2nd K712 from different seller, 41k batch, bassy, treble "OK" I guess hard to remember would heave to read my notes, but the cups clicked in their end positions of rotation so when I moved my jaw it would make a click, damn... exchange...
3rd K712. from exchange they sent me not a new one but a totally wrecked box taped up by the seller a box that had serial number different by 1 than the headphone, obviously some kind of refurb, it was again 36k batch I think, had it only shortly and of course it went back to the seller at their cost, not gonna stand for ordering new and receiving refurb in a trashed box, seemed similar sound wise to 1st 36k batch one
4th K712 from 1st seller again, 42k batch, new almost undamaged box for the first time, factory sealed this time unlike 1st from them, BUT... I could not get over the sound of it, the treble sounded off to me and IMHO it lacked 8-10kHz, it was recessed and made treble sound odd, bass was high and there as on the 41k batch one, also the pads on K712 are not deep enough for me and my ears hurt afterward
At this point after hearing the creaking, clicking, sound differences between batches my illusions of K712 being more consistent than China made AKGs went out the window. At nearly 220EUR unacceptable to deal with such inconsistencies, reference headphone? Yeah as if if they cannot even make the same headphone and it changes with each batch. I would say the K712 is indeed manufactured in Slovakia and distributor confirmed it still is, the mold for plastic is different than China made K702 and same as some old K702 made in EU or what I think were K7xx from first batches that might have also originated from the Slovakian factory where they make K712 otherwise.
BTW drivers differ and there are many variants of the K7 AKGs.
In short:
K701 driver
K702 driver used in K702, K702 AE (v1 I think thin flat memory foam pads, v2 thicker flat memory foam pads same as K712), Q701 (= K702 + foam under outer grill), IMHO also K7xx but not confirmed (thicker flat memory foam pads same as K712)
K712 driver
Hold on I will dig it out...
There you have it.
Fed up with K712 quality control and how much shops are trying to resell it's returns as new, these are big European multinational official distribution shops, not some back alley corner shop.
I ordered the AKG K702 since I liked Q701 with it's angled pads and AKG doesn't seem interested one bit to offer angled memory foam pads when asked about that. Nor have I seen aftermarket pads like that at which point modding K712 would turn into a 300 EUR endeavor by buying pads or angle adapters.
Well got the K702 and had K712 at the same time, same as I had with HD599 and K712.
Swapped the pads between them twice at the least over the course of a good few days listening to both and let me tell you... they sound very similar with equal pads so much so that it's easy to forget what you are actually listening to, period. They are not the same there are driver differences but the pads are the biggest difference of all. Neither has any foam under the outer grill I think only Q701 has from photos I've seen.
I will cover driver difference later. What do the pads do?
Flat memory foam pads = more bass + less treble volume by making driver closer to the ear, that's it it changes the volume balance between bass and treble.
Here is what happens with K702 with flat pads, it has even more bass, yes that's right, more bass than K712 because at least on my two units of these headphones in comparison the K702 driver has more high bass as in say 80-200Hz, that's what I call high bass, where as K712 has more "flat" bass that goes a tiny bit deeper into sub bass <40Hz and overall it's bass sounds a little different.
The K702 turns into a bassy headphone with same narrow soundstage as K712 has, that's the second thing this driver distance difference causes, the closer the driver the more "impact/immediateness/pain" there is from the sound and that's what makes K712 sound similar to the shallow Sennheisers except K712 has still IMHO better bass/subbass and isn't so treble shy especially high treble over 10kHz.
Now what happens with the open cell foam angled pads from K702? They put the driver more far = nice wide soundstage that I WANT from an open headphone and almost no open headphone except these K702/Q701 seem to be able to offer, I don't find the soundstage too wide or inaccurate, I think some people are simply too used to Sennheiser open headphones sound, I'm coming from a closed Senn I've been using since 2006 so that's around 11-12 years in practice and let me tell you that one is narrow soundstage so hearing these new open headphones from Sennheiser was quite disappointing.
And of course wise versa to shallower flat pad, more treble and less bass volume, the balance changes between these two parts of the spectrum.
Now driver difference, K712 has a tiny bit "more" subbass and less high bass, it seems to have the bass more "flat" where as K702 has the almost Sennheiser like peak in high bass in comparison but this peak on it is only "annoying?" (as it is annoying on modern Sennheisers especially HD5 series) WHEN you use the flat memory foam pads. With stock angled K702 pads K702 sounds fine and the bass is correct to me it simply does not go as deep, but you can do that with EQ if you want, it's pads, simple as that, will never get deep subbass with tall nice soundstage pads. K712 simply does not have this bass "peak/boost" in comparison that's about the only major difference in their driver's bass.
Treble wise I found the K712 to be a poor lottery and even the bass can be, alright lets cover the bass again ONE important thing, check your pad attachment on all AKG K7 line headphones I think some of the units as they arrive from factory may have 1 or more of the notches that lock the pads not locked and that causes loss of seal and thus loss of bass, I found this the hard way when swapping pads because the K702 open cell foam pads are more resistant when attaching and it's quite easy to not lock all 4 notches ==> loss of some bass, try lifting each of the 4 sides with a finger from outside where the notches are (up/down/left/right) if it moves up then the notch is not locked, it should not move easily up.
Treble... K712 seems a lottery with this one, 36k batches seemed to be less bassy with more treble, could be poorly attached pads but the memory foam pads are much harder to attach incorrectly so I doubt it. One was clearly sibilant, other had the 8-10kHz annoying dip, overall all the K712 seemed to go more up/down in their mids and treble compared to my K702.
The K702 I have and the only I heard, has these issues: the top position of left cup tends to creak/grind a little but still probably better than all the K712 that have tighter tolerance between parts and grind/creak even more as a result because everything is a tiny bit tighter fit. The shapes inside are all the same on K702 and K712 only molds differ between EU/China origin, EU doesn't have sharp edges on the mold on ear side, China one has. I think I prefer the looser less tight fit of the China molds that helps avoid creaking/grinding of movement of the cups more. Also almost all K712 tended to stick in front/rear end position of rotation of the cups and some may click when moving out of this position, I even recorded it on videos when returning the products.
And my K702 has nice flat mids and treble, much better probably than all the 4 K712, maybe one of the 36k batch K712 was similar.
Yes there is some 2.5kHz and 7kHz peak, I don't find this an issue at all, the whole range is fairly flat from 2.5-15.2kHz, there is a smooth "ramp up" from 1.0-2.5kHz. The bass has a boost unlike K712 and as such with the angled pads the bass is there more than when using K712+angled open cell foam pads, it only doesn't sound as deep into sub bass but almost no headphone does anyway except K712 with flat, the Beyerdynamic DTs, etc. all flat thin pad headphones.
Mixing K702, K712 and their pads, K712 with K702 pads sound nice but I still didn't like that particular unit due to it's messed up treble but it is definitely a step up over the flat pads when it comes to comfort, soundstage, getting back treble and toning down the bass impact that can be sometimes too much especially for certain games when canons fire next to you, it's just too damn loud with the flat shallow pads.
K702 with K712 pads, nice but the bass boost is too much for it, otherwise it still has better treble than the K712 for my 2 units.
Each K702 and K712 with their stock pad are fairly well "balanced" and swapping pads either is a matter of luck for particular units or K702 with flat you gotta like the bass boost and making it sound Sennheiser like. K712 is probably more forgiving for swapping to angled open cell foam pads but you have to have one with good drivers that aren't too up/down or recessed in treble (8-10kHz) which unfortunately they all seem to be only some are too much.
In the end it was "hard" to tell (easy to forget) to which one I'm listening to during normal use when both use the same pads. Of course I have songs that reveal the differences easily but for normal use it's a small difference.
And of course I liked the angled pads more due to a whole order better comfort as the pads are deeper, they do touch my ears but I can wear them all day and it doesn't cause pain, not in the order of K712.
Are the K712 worth +65% in price? Because they are made in EU which in fact seems to mean squat/nothing when it comes to AKG manufacturing? Because memory foam pads are 86EUR more expensive to make? Because K702 are transported from China at no cost using teleportation? Because K712 have perfect consistency when it comes to sound between units, meaning you buy 1 pair today and it sound the same as a pair bought a year ago? Because all units sound consistently better than K702?
NO, not really, sorry AKG. K712 is not any better from my experience than K702 or Q701.
K702/Q701 win in comfort and pleasure to listen to for music, movies, games.
K712 probably wins when it comes to say studio use, mastering/whatever/music-production-you-get-it.
Still I have seen plenty 2nd hand K712 being sold by studios in mint condition, sadly most K712 hold their price like crazy because people bought them years ago at high prices where as now it costs half of that and 2nd hand sellers do not want to go deep below the price of current new pairs.
K702 also used to cost a fortune but the price has gone down over time and especially now with production in China the cost is reasonable. At the same time though, Beyeydynamic as far as I know is still making their DTxxx line in Germany and they cost almost the same. Go figure then, the difference in cost of production and transportation between EU and Asia may not be as high anymore.
There is also the possibility that the K712 box should say assembled in Slovakia from parts made in China. That's only a speculation by me and considering each location seems to be using different mold at least the plastic parts seem to be made using different molds at different location using a tiny bit different plastic, finish quality and tolerances.
The cables though? I would not be surprised if all they do is unpack them from what they get from China as they looked very much the same, with same creases (distaces between folds), only K712 comes with cable attached to headphone which is bad AKG, bad bad bad, why bad? Because right at the headphone connector the cable is bent against the bottom of the box and all K712 cables have near permanent fold there from it.
K702 cable comes in a sealed packet, you attach it yourself, OMG so much work I want to pay 86EUR more for K712? Nope.
Oh yeah, the K712 comes with coiled cable as well, it's short around 1m and very plasticy, IMHO rubbish if you want to use a coiled cable because it's so plasticy unlike the normal cable that is fairly nice though some K712 cables were sticky/oily, IMHO releasing it's plastic softener out of them or some such.
Sound wise all the cables seemed equal to me, K712, K702, normal, coiled, all the same.
Coiled cable is not worth +86EUR either.
Hopefully I'm keeping this AKG K702 and I am glad I have tried it and did not give up completely as the current state of headphones on market is not very good when it comes to ergonomy and balanced frequency response.
The AKG K702 is fun to listen to, it has enough bass, if it does not, check and reattach your pads correctly so all 4 notches lock, soundstage is very good to me and it's not narrow as you will find on most headphones nor is it abnormally wide as some people want to complain, IMHO it's "perfect". Pads are deep enough for most people and because they are angled they help with the issue of K7 AKGs sounding a little bit too "rear", this angle helps move the driver a little more forward and let sounds come more from the front, this depends on fitment around your ears but overall the round shape of cups and pads is not good for ergonomy as it easily invades at front into your jaw and I can even see the headphone in my peripheral vision how big they are front-rear width wise. The top-bottom height is fine. They need to make them oval but AKG probably doesn't care and want to improve their ergonomy as it would "ruin" their "signature" look and be similar to Sennheiser.
Another ergonomy thing is the headband, OMG the headband. Leather difference between K712 and K712, I would say none, they are both stiff only K712 has narrower cut which is actually worse because then only the front edge of it will cut into your head. You gotta get some padding for the headband, why doesn't AKG put some there is beyond me. I've cut a 2.5 thick by 5.0cm wide piece of open cell foam, attached it with those twisting wire thingies that are used to hold folded cables together, though now I use a hook and loop that is otherwise used for the same purpose of holding cables, except this hood and loop is the correct size, no need to cut anything and it's outer side is soft almost velour like, I got them with my computer PSU from EVGA. No idea if you could buy them somewhere, I suppose try looking at ebay/aliexpress if you want them. I've also tried slightly wider foam as I cut my existing piece in 2/5 3/5 ratio or there about but I found the wider piece was keeping the headphones a little too high, the narrower one is perfect.
Ebay/aliex also has options for some knitted padding from China. Or you could buy and glue on HD600 padding for a couple EUR from China.
Using zip ties on the posts to stop the headband moving too far and dropping the headphone works but it puts even more pressure on to of your head under the hard leather headband, I could not stand that for long, it's painful. Works yes but so painful.
Get a padding, if it's still too high or low get different thickness or width.
Done, that's all the modding a new K7 headphone needs. Of course the rubber bands don't last forever and will weaken over time, still it's user fixable, same with the loose wires falling off of the driver, oh well suck, but you can resolder/replace that.
Pads are easy to change but not cheap to buy original ones from official distribution, pricey to say the least. And the ones found on ebay/aliex are probably all knock offs with who knows what change in sound that might do.
Clamping force on AKG K7 is OK, not too high not too low, about just right. Beyers are skull craking and the metal band is very very difficult to bend, Sennheiser new are skull cracking a bit too but they do soften out since it's all just flimsy plastic especially flimsy plastic joints that probably break if you sneeze.
Sometimes I find it hard to take the AKG K702 off, it is such a pleasure to listen to music with them.
My unit doesn't lack bass, doesn't have sibilant treble or other treble issues that would annoy me. The only treble issue I found when comparing is that there may be a dip at 7.5kHz more than the K712 unit but it seems fairly short dip, plus my ears hear 7kHz more left and 8kHz more right, still even with that I would say there is a dip on my K702 at 7.5kHz that was not present on the K712 to such degree. Otherwise "purrfection".
Music, movies, gaming, very nice. Sure games may take getting used to for the first couple days or week if you go to K702 from a closed narrow headphone or even from K712 as sounds are now more far and less "loud/immediate/painful/impactful" but once you get used to it it does sound more realistic with much better sense of space around you. Music especially when made right sounds as if you are there listening to the music live instead of music being played inside your head or in your ears way too close and narrow. I didn't get that feeling with HD600, it was more wide and less strained than HD599 but not as open and wide as Q701.
If you have not given a try to K702 or Q701, I can recommend them unlike all the Beyerdynamics, Sennheisers, AudioTechicas, ... that I have listened to in this 100-200EUR price range. With Sennheiser you have to go very high in price to get decent sound quality these days IMHO, to HD600-650-660 probably skip 700 and try 800, pricey. Beyers, pass, V shaped for bass heads and I do like me good bass but what is too much is too much, and the "ear killing" treble. AudioTechnicas... good luck finding a good one, MSR7 closed is neat but not perfect and heavy as a brick, the open ones cost a fortune again with thin flat pads and notorious lack of bass.
I do not know if Q701 are manufactured still, I think they may not be and they certainly are not worth their insane price, all the difference as far as I know is a couple rings of foam under the outer grill.
AKG K702 is the best deal IMHO from K7 line up, detachable cable, nice box LOL nicer inside than K712, different paper and print than K712 too looks more cheap on outside more China like where as K712 box is a little thicker paper but glossy black print but the print scratches off on the edges, on K702 box it does not scratch of so easily and it's matte, white on K702 box is more chemical clean pure white, K712 is more natural yellower white.
OK I will stop now, it's long and should be all I can remember.
Locally, totally inflated to ridiculous compared to 5 years ago when it went up and up for 3 years. Around +25% in price. In Germany... if you wait a 6 months you can jump over the insane peaks of +50% in price, they have these huge swings. Now since April it's back where it was ages ago.
Sort of the budgetlightforum.com of headphones instead of flashlights.