Pros: Good value, balanced, accurate. Audiophile grade sound for a bargain.
Cons: Larger heads might have fit and/or comfort issues. Lacks bass impact compared to higher end competitors.
I got my pair on sale for $150 USD. I have had a few lower end AKG headphones and have never been disappointed with the value and sound signature they offered. It's been a long time coming but I was finally able to get a higher end AKG in the K612 Pro. In this review I will be comparing it head to head with the venerable Sennheiser HD 600. Here in Canada the HD 600 is about double the price but offers a good benchmark to compare with.
My source in testing is the 1/4inch headphone output of my TEAC UD-H01 DAC/Amp connected via USB to my Windows 8.1 desktop. I use the foobar2000 player with EQ off playing various files from FLAC to m4a to mp3 (VBR/CBR 320). In terms of sound signature preferences I like more mid centric headphones with tight, accurate bass (quality over quantity). I frequently have long listening sessions and I do get irritated by sibilance on certain bright headphones like the DT 990. I enjoy all genres of music spanning across many different era's. Enough about me, I've had this headphone for a few weeks now and after 50+ hours of burn in and constant use I am happy to share my experience.
Packaging is average nothing too fancy. Upon opening the Velcro lid on the box the headphone is sitting in a plastic bag with warranty card in the box. The 3 meter cable comes with the 1/4 inch screw on adapter attached. The cable is not replaceable but is of reasonable thickness and should hold up to abuse. The first thing I was drawn to was the real leather headband with quality stitching and AKG engraving. A really nice touch at this price point. The headband is also flat on the inside vs the bumpy one on the Q701. To keep cost down this unit is made in China though.
Ear cups are plastic with black and silver metal grills. The ear cups do tilt up and down but do not rotate flat. The replaceable ear pads are a thick and plush padding with velour covering. Simply twist to unlock and they pull right off. Over the inside of the drivers is a thin padding with a 1/2 inch circular cutout in the center to expose the driver to the ear. The padding is then covered with a soft breathable nylon material which is attached to the replaceable ear pad. The nylon feels great on the skin if the ear should ever touch the inside. The nylon covering is a nice touch. Most headphones, including the more expensive HD 600, leave the inner foam exposed.
Right and left are large and clearly marked. It's a small detail but I like to be able to tell which side is which in the dark. The top right side of the leather headband has a small engraved graphic, not sure if it was AKG's intention, but it serves the purpose well. The outer headband portion is made of two steel bars with plastic coating. The auto adjusting headband design used on the K612 is a unique feature to AKG taken from the K701/Q701. The inner leather headband is suspended with elastic nylon strings and moves along the tracks of the outer steel portion held together with plastic guides. It seems to work well, it slides up and down quietly and effortlessly.
Style wise I really like the simple black and silver color scheme. It looks nearly identical to the K702/Q701 (black). On the head they do appear huge though because of the dual headband design. Overall the materials, look and feel reflects the price. You know you're holding a professional grade piece of equipment. The main difference between this and the Q701/K702 in terms of design is the cable. Honestly though, as an owner of headphones with removable cables, it's an overrated feature. Connectors are bulky and wear out. If you take care the cable will last a lifetime. I have yet to actually "need" to replace the cable on any headphone of this quality. I can't personally comment on long term durability of the design yet, however, it's been in use by AKG for decades now.
After several weeks clamping force is light to moderate. But this can be formed by bending the outer metal headband to your liking. There is plenty of flex in the headband. At only 238 grams comfort on the ears was never a problem. I did not have any issues with sweat either. However, I did have a bit of a hotspot on the top of my head after 2 or more hours. As nice as the leather headband is, it's not padded at all. The nylon elastic part forming the auto adjust feature pulls the headband down even more. The larger your head, the farther the elastics will be stretched, and the harder they will push down. I have an average size head and I felt it. So people with large noggins might have a more serious issue.
I tried to remedy this by forming the leather headband in an arc to conform to the top of my head better. Then I stretched the elastics out by hand being careful not to stretch them to breaking point. This helped but I still find myself pushing it up periodically to relieve pressure. I anticipate this should be less of an issue as the elastics stretch over time.
Another note for those with large noggins. I only have one fingers width of clearance left on the top of my head for adjustment. That really isn't very big at all since I have an average size head. On my HD 600 I am only half way up the available adjustment. Comfort wise I give a clear edge to the HD 600 because of the larger oval ear cups and superior headband support, despite being 20 grams heavier. In terms of durability I would say they are about the same. Style wise the HD 600 probably looks fancier with the granite counter top like finish and larger see through metal grills.
Boy do the K612's like power! At only 120Ohms they require more power than the 300Ohm HD 600 to achieve the same volume. On my TEAC UD-H01 it needs about 15-20% more power. That being said I could drive it from moderate to ear bleeding levels from 11 to 12'oclock on the volume knob. My TEAC is not considered very powerful (40mw RMS at 32Ohm) so I would say anyone with a modern desktop or even portable amp should be fine. I did not test the K612 without the amp, but from what I have read mobiles and onboard audio devices usually don't cut it. Unless they have built in amplifiers. They are totally open and offer no isolation. Sound leakage is significant, on par with the HD 600. The sound did not seem to change at all before or after 50+ hours of burn in.
If I was to use a single word to describe the sound signature of the K612 it would be "accurate". It really is very accurate across the entire spectrum. It's very neutral, even more so than the HD 600. I consider the HD 600 a bit more forward in the mids and slightly more rolled off on the highs. More laid back I guess you could say. So I was worried that the highs could get irritating, as they did on my testing of the DT 990. So I threw some Kenny G at them on high volume. After more than an hour I experienced no irritation at all. No sibilance whatsoever.
A track I love to test imaging and soundstage with is Letter by Yosi Horikawa. The K612 was impressive, on par with the HD600 for sure. Truly great at this price point. The only real weak point for some will be in bass response. Although very tight and accurate, it lacks a bit of oomph compared to the HD 600. You just don't get as much impact. This really doesn't take away from anything else though, and you still hear the low tones right down to 12hz. It's just not going to please those bass heads among us. Heck, even the HD 600 is considered light on bass by many.
The HD 600 still has the incredible ability to resolve details and present them in a more natural way. It's hard to explain but all the little nuances in vocals and stringed instruments are brought out a bit more. You hear them on the K612 too though, just not quite as clearly. It's something you wouldn't miss that you could only tell by a direct side by side comparison. This slight improvement will be enough to justify the upgrade for some. All things considered the K612 is still among the best sounding headphones in its class.
I consider the K612 an improvement over the Q701 at a lower price point. Not only is the headband more comfortable, the highs are less irritating, and the bass is fuller. AKG has never had a better sounding headphone at a lower price point. Audiophiles will be pleased with the reproduction on this headphone. The only real competitor in its price range is the Audio Technica AD900X. But I think more people will prefer the sound signature of the K612, it works better across more genres. A lot of people have fit/comfort issues with the headband on the Audio Technica's too.
Although I do think the HD 600 is more comfortable, natural, and revealing with improved bass. I am keeping the K612. It's rare to find a headphone in this price range that has such a versatile sound signature. I would not hesitate to buy it again. It's a great bargain under $200.