Ok well I auditioned both the AKG k845bt and the Sony 1RBT MKII yesterday one after the other. These are my thoughts overall on them. Basically a review comparison.
Sound wise overall they were both quite similar. Both had a good wide soundstage and good attention to detail in all ranges. The AKG extended deeper in the bass than the Sony and I felt the bass was more clean. The Sony wasn't muddy by any means but it seemed to have a slight mid bass hump which got annoying to me in some instances. The AKG was boosted in the bass but this was more in the sub bass region. The Sony also seemed to be slightly veiled in the vocals compared to the AKG when it came to male vocals. Female vocals didn't really have this issue.
Both headphones had some sibilance to them. The massive sibilance I experienced on the last Sony that I tested out wasn't there which makes me susupect that it was a burn in issue (don't think the MKII would have arrived at the store all that long ago before then). It was still annoying enough that I couldn't listen to a few songs with but didn't distract me most of the time. The AKG's sibilance was lower and didn't really bother me unless I looked for it. Other than that the sound was quite balanced for both of them. Definitely the best two bluetooth headphones I have heard.
Sound quality varied also depending on the source I was listening to. Youtube videos and low bitrate mp3 were definitely better on the AKG. The bass was cleaner and more even, the vocals were clearer though the upper mids and highs were pretty much the same for both of them. For higher quality mp3 it was similar to the lower quality recordings though the sound was obviously much better. The bass and vocals I felt were still superior on the AKG in the same way though both were obviously much clearer than either one was on the poorer recordings. The Sony having aptx and the AKG not having them didn't make a difference so far to me. The AKG was still superior most of the time.
Earlier in the thread @tinyman392 had mentioned that aptx only really becomes an issue of importance for FLAC files. This was definitely the case here. When listening to FLACs the Sony came out on top. The AKG wasn't bad by any means and the quality was definitely better than any of the mp3's that I listened to but I did notice some artifacts that I don't normally hear in my FLAC files. These artifacts were not present in the 1RBT. To see how much impact aptx was having on the FLAC files I tried the Sony MDR 10RBT as well with the aptx enabled. The artifacts weren't present here either but the overall sound quality was still much poorer than the AKG. Lack of aptx did reduce the sound quality on the AKG below the similar quality 1RBT for FLAC files but not enough to make it sound worse than much lower quality headphones like the 10RBT. When I connected them both via cable the artifacts disappeared on the AKG and the sound differences between the two were similar to what I wrote earlier.
Comfort wise I've got big ears so I was expecting this but neither of them actually fit around my ear properly. I don't think the AKG was designed to actually fit around the ears anyway since they use round cups. They sat my my earlobes and the top of my ears. The Sony will fit around the ears of someone with smaller ears no problems I would imagine but for me they sat on my ears the same way as the AKG. The Sony was slightly heavier though they were both quite comfortable. The ear cups pivot a fair bit so crushing shouldn't be an issue. Had no issues concerning crushing of the ears though the AKG did make my ears annoyingly itchy after a while. I was worried the AKG would hurt the top of my head a lot since it lacked padding on the headband but I didn't find it an issue over my listening period. Other people have complained about this though.
Isolation wasn't the greatest on both (though decent enough) but the Sony did do a better job. I imagine though if listening on a train they both would be fine/ Leakage was a big issue for the AKG however. They seemed more like semi open cans than closed ones with the amount that was leaking. Not an issue at low volumes though when I cranked it up the guy next next to me could tell what I was listening to. Could also be due to me not really getting a good seal on them. When I pushed the ear cups to my ears leakage was no longer an issue. The ear pads use memory foam so perhaps after using them for a while the seal will get better and leakage drop. The Sony had no problems regarding leakage.
Call quality seemed fine for both of them though the AKG did a better job with the microphone. I could hear the other person fine with both but on the Sony they could tell I was using headphones. Not so with the AKG. The AKG does seem a bit fiddly with the bluetooth. Connecting is fine but it is hard to know whether bluetooth has turned off or not when you try to turn it off. Didn't use it long enough to know how big an impact it might have on the battery life (which is already low on the AKG) however. The Sony has a better array of buttons as well. The AKG seems to lack media buttons aside from Play/Pause. Both are said to have NFC though I didn't try it for either.
Overall neither of them are the ultimate bluetooth headphones for me and I wouldn't jump on either one just yet. Want to see some other ones first but if I had to pick out of the two, I'd pick the AKG. Suits me better for my needs.
tl;dr. The AKG was more balanced overall and sounded better for everything apart from FLAC files. Comfort and isolation though would be better on the Sony.
Edited by n00b2 - 5/1/14 at 10:53pm