Firstly I would like to add a little background. I own a pair of Austrian made AKG K601s for around 13 years and through the years I have listened to many other headphones (Sennheiser, other AKGs, Sony etc.), but to be honest none were more expensive than 200€. Sadly none came even close to the reference sound of the K601s. Although the K601s are still in perfect working order, I have decided to add the K712 PROs to my collection. I will therefore add some comparisons between the two.
I would describe myself as being very picky in audio quality, and can appreciate superb audio reproduction with low distortion and wide frequency response. The audio gear I am using is an integrated amplifier Denon PMA-1600NE+DCD-720AE and internal PC sound card Creative AE-5. Both can drive up to 600 ohm load.
It is without saying that I had very high expectations for the K712s, and oh boy do they deliver! I didn`t want to rush with my assessment too quickly when connecting them for the first time. I do believe in burn-in process from my past experiences with speakers and headphones. Listened to K712s for an hour and they were very good, but I let them play for about 20-25 hours before having a proper listen. I would say they needed about 50 hours to get to the point I stopped to notice further improvements in sound, so please have that in mind if buying. Just my humble opinion.
First thing that really got my attention is how much detail in sound these have. Compared to K601s, the detail in sound on the 712s is simply on a whole another level. Quality of the recording makes more difference and really pays off when it`s FLAC for example. Directly compared, the K601s now sound a tad more muffled. Soundstage is similar between the two and altogether phenomenal, but 712s are just slightly more intimate and less distant. I now see what they meant, when they said the K601/701 have a massive soundstage. I listen to a whole lot of genres, but mostly old rock, electro-house, pop, reggae, and the 712s can take on anything. They really do excel in electronic stuff, and if I`m really nitpicking, maybe being the weakest in classic rock in my opinion. Bass and treble being slightly better than mids, but altogether have a very natural and clean sound.
The 712s do have a less flat freq. response than 601s, but I do use the EQ for the 3-4kHz dip, which is noticeable if not corrected a bit. They respond really well to added lower bass on EQ. There is no sibilance in any music, so that is really nice when listening for longer durations. No ear fatigue for me. I was always impressed with 601s comfort, but 712s are even better. Clamping force si low and pads are really nice, so comfort is 10/10. Construction quality is maybe the weakest link for AKG brand, so I do handle them carefully, because the plastics on the headband can break and the elastic bands do stretch through years. I always hang them on the outer plastic part of the headband. They are Made in Slovakia.
In the future I will try to get a listen on Sennheiser HD600/650s for comparison. To sum it up, I would really be surprised if the K712 PROs would not be (one of) the best to at least 400€.