unfortunatelly ill have to bid farewell to you, good people of this topic, the px has to be sent back.
some people in the future might find my experiences helpful so here is why.
(((the story so far. my christmas gift from my family was a pair of noise cancelling headphoes of my choice. my use was to be home use with a pc, excluding the damned noisy neighbours of my life. most sources acclaimed the bose qc 35 and sony wh-1000xm2. as the bose doesnt support aptx i chose the sony. i was quite content with it, anc is superb, sq is good, comfortable, extensive app options. on the bad side noticeable latency - i set my video player to -150ms i think -, plasticky feel, stupid auto turn-off. then, after 2-3 days i could hear a constant pink noise-like hissing on the left and i sent it back. the second pair of sony showed the same issue on the right side after only one day (NOT my ears!), plus the dreaded headband cackling. sent it back, and thought about my next move. of the sennheiser hd1 only the pink floyd edition is available in my country, expensive as hell and ugly, the pxc 550 pricey and reportedly inferior anc compared to the bose and sony, i didnt want the bose because of the lack of aptx, there arent too many good opinions around of the plantronics - so i started to read up on the px and the b&o h9. there werent direct comparisons in the matter of anc to the bose/sony level, so i asked around here - thanks folks for the replies! - and chose the px.)))
first day.
-these are one sexy pair of headphones. not as pretty as on the pictures but photoshop could make even me prettier.
-there was a lot of pressure on my head (i think i have a medium-sized head) + a very uncomfortable sense of pressure in my ears, both resulting in a feeling just this side of a headache. still, im a you-break-me-in i-break-you-in kinda guy (had a few martens boots in my youth) and didnt lose hope.
-range is great, they almost never skipped when venturing to the kitchen or bathroom. the sony was worse.
-build seems to be very convincing. they look and feel as they could last a decade or more (at least structurally).
-on/off sensors are stupid. i take them off, nothing happens, take them back on, the music stops. still this can be adjusted in the phone app, so again i didnt care much (i dont own an android or apple phone, playing with the app requires of me a short trip to my brother)
-connecting to pc is a hassle. after sending the cans and my pc (and myself) to sleep and wake all the aforementioned up in different order the px connects automatically to the pc (via a logilink aptx capable csr dongle) but theres no sound. i had to open bt devices, enter the headphone profiles window, disconnect the a2dp profile and reconnect it. this is absurd to do twice a day, there was no need to jump such hoops with the sony. i did everything i could (power management in windows, pm of the dongle, setting autoconnect in the bt software), nothing helped.
second/third day.
-comfort got much better.
-became a hesitant believer of the burn-in theory though im still not sure if the cans burn in or my ears get used to their sound. (< means sound got better for me.)
-played around a bit and to my greatest surprise i found that there is no noticeable bt lag. to my knowledge it is unheard of with aptx hd headphones!!!
-played around with anc. my greatest grief with my neighbours is the thumping noise of the kids running around and drumming, same family, two floors(!) above so in my case the anc has to do a good job in low frequencies. the sony did a great job of this, so did a bose qc 25 that was lent to me. a quick test revealed (me beating my desk with my nails, me thumping a wall with my palm, neither of them hard) that the px does next to nothing with these kind of noises. i didnt get desperate (yet) as i (dis)remembered i read somewhere that the default level of anc is not the strongest and voice pass-through might be enabled - lets see the app first, i thought.
-in the garden next to our house people did some work (20 meters at least). my window was open a bit (10cm) and though i couldnt hear what they talk about i could very clearly hear them - with anc on. again, i didnt lose hope, see the point above.
fourth day.
-its weekend, my neighbours are most active this time of the week. anc didnt do much with the incoming sensory assaults, so i rode to my brother - lets see that app! a most disappointing result: anc was on its maximum already and voice passthru was off. so i had to realize: from this pair of cans i can only expect this much (next to nothing) in the matter of defending me from the outside world - desperation beckons... i decided to leave the pair with my brother to play with them a bit and i will send them back next week...
i left out a few things that many people discussed before, yes, sq is usb-c > bt aptx; anc off > anc on. the 8x pairing, 2x connection is great.
im not sure where to go from here. anything that might be better is even more expensive. i think ill get a denon ah-gc20 which is far from being acclaimed much but according to the measurements of rtings.com they do a great (not excellent) job on low frequency noise cancelling. if thats not enough ill move backwards (mobility, possibly sq-wise), bite the bullet and acquire a bose qc 25...
anyway, i was warned and can only repeat: these are great cans, plenty to love here but if youre looking for a pair of anc headphones, forget these. think of the anc of the px as an added extra feature - you shouldnt buy these with anc in mind.
so so long and thanks for all the fish (and replies and advices and information)!