Austrian Audio Hi-X55

Pro's:
Very comfortable
detachable cable
folds up nicely
feels high quality
clarity in the high-mids
makes a bad mix sound bad

Cons:
Makes a good mix sound bad
huge frequency bumb in the high mids
uneven/strange soundstage
a far less expensive headphone can give you a more accurate mix
the sound is not representative of the actual mix and recording.

First impression:
The Hi-X55’s are MUCH more comfortable than my Sennheiser HD-25’s. Very nice.
I’ll be using these for tracking in my home studio so I need to be able to move around, have little or no bleed, and have an honest sound reference. I need to trust them while getting sounds.
I Like that they have a long cable. Great for tracking.
I like that the cable jack is on the left. My rack is on the left. Perfect. They are lightweight. Nice.

Sound: My first impression is that vocals on songs that I know well are unnaturally boosted. More than I’ve heard before in a headphone. Also the sound stage is noticeably narrow. More like a triangle right in front of my face rather than a full left to right stereo image.

I plug into my RME Fireface UFX and listen to “Everybody’s Gotta Learn Sometimes” recorded by John Brion with Beck singing. A well recorded, super clean song with all the components of a good reference track.
I’ve listened to this track as a reference, over the years on multiple speakers, in high end studios, in venues, in my car, on my Audeze LCD-X headphones, My Neumann speakers, my Auratone speakers, and my pair of Sennheiser HD-25 tracking phones. I know how this song sounds in the world.

With the Hi-X55 headphones the song sounds “different” I suddenly hear the acoustic guitar sounds like plastic, the vocal harmonies seem to over-power the main vocal in the chours. I hear things I’ve never heard before in the song, it’s true, but the sound signature is “wrong”.
The song does not sound this way anywhere else except in the Hi-X55. That, in my opinion, is bad. On all other reference devices listed above, the ears focus on certain parts of the mix in the same way. The song makes sense. With the Hi-X55’s it’s a different tilt, a different intention, a different feel, another angle. It just sounds “off”. Hard to explain, but what I want most is the truth so I can apply that to finding sounds that are honest while I’m recording or listening back to a song.
My first impression is I can’t do that with the Hi-X55 headphones.
I bought these because in multiple reviews they were called “flat” and “neutral” sounding heaphones. I can 100% tell you right now these are NOT FLAT headphones. There is a easily noticable bump in the high-mid frequencies around the area of the voice, snare, etc.
When I apply some eq in “Total Mix” things start to sound better. That’s a good sign, but if I have to eq them to get them to sound right why not buy a much less expensive set of headhones?
I would say they are not usable as mixing headphones because their peculiar sound signature is not representative of the true sound of the song.
I put them up against the Beyerdynamic DT-770 Pro 80 Ohm The Beyer sounds better and is a more accurate reference headphone. The Beyer is a little less comfortable, has about the same amount of bleed, has the same size cable on the same side (non-detachable) and is half the price of the Hi-X55. Goodbye Austrian Audio, Hello Beyer!

I bought these headphones for isolation and tracking. And to be short they perfectly fit these 2 purposes.

Build quality
Hi-X55 are solid. Very nice combination of metal, plastic and pleather. They are not fancy by any means while they have this truly professional look. Work horses!

Sound
Crisp and clear. Analytical and unforgiving. You won't enjoy most of the music in these. Highs are quite accentuated. Bad mixes sound harsh! The bass is there but it's not as groovy as in Beyerdynamics. The manufacturer describes Hi-X55 as first headphones that have perfect transient attack. This is true. You almost physically feel percussion and plucky sounds - very snappy.

Stereo panorama
These have very wide stereo field like open cans. Very easy to locate instrument panning and sound directions. Great for analysing mixes. Great for gaming too!

Comfort
These headphones are relatively small but they have the right shape to fully cover your ear - your ear doesn't touch the headphones and perfectly sits inside the oval earpad. Due to closed design you have good isolation but it also creates some sort of vacuum between your ears and the caps (because of the pleather pads) which some may find uncomfortable.

Isolation
Isolation is very good! It's quite better than in Beyerdynamic 770.

Cons
It's very relative con but keep in mind you won't enjoy most of the music in these. You will hear harsh highs and resonances in bad mixes which you usually don't hear. These were designed for professional work and not for amusement.

Price / Quality
I think these headphones have a very solid price to performance rating. I highly recommend them!

I bought the Hi-X55 headphones as a replacement for my 10+ year old AKG K-271 MKII (still made in Austria). I use them for pretty much everything, from listening to music, playing piano and guitar, to virtual meetings and video streaming. While the AKGs are great headphones, I find them uncomfortable to wear for more than 2 hours at a time, and decided on the Hi-X55 due to their circumaural design.

Over the years, I've grown used to the neutral sound that studio headphones deliver, and the Hi-X55 is no exception. That's to say that if you're looking for loads of bass, look elsewhere. However, the clarity and dynamics are exceptional, and I think the Hi-X55 is a true improvement over my AKGs.

To illustrate the point: when I first plugged them in, I thought they sounded terribly harsh and compressed, until I realized that my Spotify Audio Quality settings were on "Automatic" (which I didn't find to be a problem with my AKGs). After changing the setting to "Very High", I was absolute blown away and, after a few weeks of daily usage, I can highly recommend the Hi-X55s.

That being said, there's one major design flaw which I find hard to get over (and reason enough to only award 4 stars to these otherwise exceptionally good headphones): the cable plug is based on a 2.5 mm (!) stereo jack, and uses a proprietary bayonette design, which means that your only options are the 3m and 1.2m cables that Austrian Audio offers. I really don't understand this design choice, and I think a standard 3.5 mm jack without the proprietary bayonette would lead to a much improved user experience. I guess it's not a problem if those options work for you, but I really like using my headphones with spiral cables, and at the very least Austrian Audio should offer a spiral cable option (I ended up making my own spiral cable, which was unnecessarily painful).

The build quality is top notch. Tho I have to mention that the rotation of cups is a lot looser on the left side on the right, but other then that, a very well made headphone.
Tho I am worried about clicking I hear from the plastic bits when the headphone clicks to place. When adjusting my headphones on my head with not much force, you can hear the metal parts move against the plastic as if it's going to take the plastic apart.
That was the bit from my K550 headphone which broke too and it looks similar.

If you mix mostly on monitors, certainly get them to check problems areas on. They will stand out immediately. I especially liked them for vocal work (both interview and music vocal mixing.)

However, I feel like the comfort is lacking which is a shame.
Many reviewers praise it but I have a feeling that they don't sit more than 4 hours with it on. It's a tad too heavy which also causes the headphones to creep forward every time you look down.
This sucks because the passive noise reduction is absolutely fantastic.

Also something to look out for is that the cable is really loud compared to other headphones which is annoying when drumming/moving with them. From 40cm down the cable, if you softly tap on it, it sounds like someone is tapping on the cup directly.

Soundstage is fine.

Still debating whether I am keeping this since I do sit for long hours with them on.

EDIT: after mailing with Austrian Audio, the loose left ear was indeed an issue with my specific headphone. This is also what caused the discomfort.

I want to leave this review up incase anyone else has this issue but I did adjust the stars according to as if my headphone would function like most likely your new one.