The following review is my impression of the K702, based upon working on mixing and mastering processes with them in my music studio.
Today after 100 hours I can say that I can trust my K702 100% as my best studio monitor headphones. It's very easy to navigate with them through the frequency response scale within the sound stage environment. The sound is very smooth, airy and clean; no artificial noise, due to the perfect axis in the 3D sound stage. This means the depth is equal to the stereo image which is equal to the frequency response. This brings better instrument separation and musical details to the sound. With these abilities I can be anywhere in the mix and the best thing about it is that I can match the K702 sound with my speaker monitors. (I have to comment here, most of the headphones have problems creating this depth in the 3D sound image.)
First, I was a little wary when I saw the frequency response graph on the Headroom site. When I got my chance to listen to the K702 and compare them to the 271MKll and the K240MKll on the SPL Phonitor, I realized that this frequency response graph is divided by the expansive K702 sound stage. I still don't know if it makes any sense but with this coloration, it still sounds very balanced, especially when you compare them to the monitor speakers or to my other flat FR cans.
A member mentioned on the forum that with the K70X you can hear the end of the reverb tails, and it's true. This is what I call "musical details". It's very easy to hear distortion on the sound, especially when you are mastering or cleaning noise in the mix. The other thing that I appreciate about them is that they are not laid back and not fast. This means that the sound is very stable and doesn't move forward or backwards when you use compression or EQ on several channels as a dynamic process on a track.
No matter what kind of music I'm working on in the studio, I found that the K702 will create the best results. Until I had the chance to own the K702, I was relying on a few different headphones, in that each one gave me a different view and characteristic of the sound. With the K702, I don't have to use any other headphones to check the references anymore. They do the job completely. In my ongoing search for the best studio monitor headphones, these are at the top of the list, so far.
Review update, 11. 1. 2014
Since I've did this review / impression back in 2008 and After cheeking for a few years what will be the best amp for the K702 I've come to the same conclusion that I've start with back in 2007, the SPL Phonitor is the best amp for the K702. For studio applications I didn't found any solid state amp out there that can compete with the Phonitor in terms of transparency and sound separation, and the most important for me is the long sessions in the studio with no ear fatigue! The Phonitor is a very balanced sounding hps amp, and they use the nine SUPRA OP amps that made and developed by SPL (120V technology), same technology as in the SPL MMC 1 @ 8K mastering console, and the SPL PQ 2050 mastering edition EQ @ 15K.
Over a few years I had the opportunity to compare the K702 to other high end hps, like the Sony Qualia 010, T1, HD-800, HE-500, Stax 4070. As well the K702 is the cheapest one on this list, a high end hps with a mid range price.
The Sony Qualia are a great hps and the most balanced sounding out there, but out of my price range and I was not so pleased with the Qualia sound stage.
The Beyer T1, are the closest one to 702s sound concept and yet not natural as the K702 with the Phonitor combo. Here is more info of my studio impression, http://www.head-fi.org/t/595522/akg-k702-vs-beyerdynamic-t1-in-the-studio
About the HE-500 with the Phonitor combo I didn't like it so much, but the upper mids are good and maybe the best part for me about those hps.
The HD-800 are very expensive hps and yet very popular hps on head-fi. I had a few sessions with the HD-800 and every time after about 20-30 minutes into the session I've found the treble spike of the HD-800 to kick in and start annoying my ears, especially with electronic music that have a lot of energy going on in the treble area. I cant afford my self to burn my ears because of the HD-800 treble spikes, so for me the 800s are out of the race after 20 minutes with the Phonitor combo.
The Stax 4070 are the most promising monitoring tool so far, I was very impressed with the sound concept of the 4070s, but to get them in my studio up and working I'll need to sale the Phonitor and bring some other amps to fit the 4070s for my best needs. As well I would like to try out the Stax SR-009 first.
At this point in time, is the beginning of 2014 and the AKG new flagship hps is out, the K812. I would like to try them out very much unfortunately I'm not in the U.S any more, I've moved back to Israel and here at the kley zemer music store (AKG main and only distributor in Israel) they sale the K-271 MKll which are the most advance AKG hps in their store for 1000 nis ($287). A year ago I've asked if they'll import the K702 and they told me the K702 will be too expensive to be sold in Israel. So, I don't think they will ever sale the K812 here in Israel.
I'm still a bit optimistic and I didn't totally give up yet on the K812, I hope soon I'll have the opportunity to check them out and compare them to the K702 on the Phonitor.
In the meantime in a parallel universe as a electronic music producer and mastering engineer I have long mixing sessions in my studio, I mean after 5-6 hours on my speakers my ears starting to get tired at this point I want to change to a different reference system. In those moments I'm very happy to power up the Phonitor and get into the micro details of my musical word of mixing and my mastering with the K702.
Another issue with the K70X series is the cable, I've found out you can improve the sound by 10-20% with a better cable. Here is more info and some great impressions, http://www.head-fi.org/t/378255/akg-k702-build-your-own-cable
The SPL MMC 1 mastering console.
SPL PQ 2050 mastering edition EQ.
Edited by Acix - 1/12/14 at 4:33am