It's early days, and I am not a researcher, or academic, and not sure if this thread is the right place to post this. But since some of the "trouble" started with my initially terrible experience with the Zero 2, might as well post it here.
Long story short, I have flip flopped between two IEM's the ARTTI T10, and the Zero 2 in terms of preference, but through extensive listening and actions listed below, I am now enthralled by both of them. Each which brings their own very impressive slant to the listening experience. But this was not achieved overnight. And the steps that led to the acceptance and appreciation of each of these, has common aspects.
1. It takes time to learn, and for the ear to learn to hear better, as one encounters more resolving devices, than one has been accustomed to.
2. Based on my limited experience, with just these two, I do not think one can expect optimal performance from any listening device, stock, unless one is lucky that one's listening preferences just happen to exactly match the stock item. I have discovered that there is immense scope for "tuning" the performance of an IEM, and in my case, it's all done in software, no physical alchemy involved.
3. Iron sharpens iron. Each listening device gives us a window into what is possible, that is good, and we are able to take the insights gained from listening to one device, to challenge our optimisation efforts with other devices. In a round robin, lessons learned about improving one of a couple of IEM's fed into the optimisation of other IEMs. In an ever improving increment. Am convinced that it is optimal to own a few devices, for the purpose of learning, and that includes, the not so good ones, cos they teach us what to listen out for, and show us what bad sounds like. How do you cure a disease if you do not know what to look for. I.e to weed out the sore points of an IEM, you have to hear and know what needs fixing. Furthermore - the correct end result, will have something in common across good performing devices, so listening to them reinforces good, and teaches us to steer away from bad.
4. My goodness, 50% of good sound is fit. Getting a good fit that one does not adjust every few minutes, is heaven. Does wonders to accurately hearing the bass. and mids.
5. I have found benefit in using a wider bore than the stock tips, which opens the sound (i.e the throat) of the IEM. I hypothesise that manufacturers deliberately supply small and medium bore eartips, to cover up anomalies in the higher frequencies.
6. In my case, I note that the Harman 2019 v2 curve is one to be respected, not followed hook line and sinker, but when I have used it as a guide, in any manual EQ tweaks, I get better more insightful sound. Hope this is NOT placebo.
7. Playback volume is of the utmost importance. Comparing things at the same volume, cos louder will sound better. So many of the impressions expressed about devices, have no common foundation such as - what level of loudness was the human observation made, so it is hard to align human opinions, cos we are not comparing like with like.
8. Some products like the ARTTI T10, are like diamonds in the rough, great potential, but need a fair amount of EQ to chip away the rough edges and let the jewel shine. I've finally got it to sound really good, far better than the stock sound - which had begun to give me concern. and it sound amazing now, with all the issues I had complained about gone - now have pin point 3D accurate positioning of all elements, natural sound, no fatigue, still balanced if nevertheless still airy, with a high frequency that seems to go on forever, but the harshness is gone. Scarily resolving. Hearing things I could not believe were possible to hear in a recording.
Other products like the Zero 2, are pretty close to their optimum @ stock, even without EQ. But still respond to EQ well.
9. I think distortion is important to weed out, in the choice of products. My brief look at AmirM's reviews, arrives at a layman's conclusion, very likely important as a factor, Especially where extensive EQ will be applied, really important one is not also.
10. Part of the flip flopping of opinions, was caused by user error. I was using the same Crossfeed settings, for all IEMs. And this especially did not work well for the T10, so now each IEM is cycled through a number of crossfeed "presets", to identify what fits best. Because crossfeed is a key optimisation, in my listening, I have to set this on an IEM specific basis, not a one size fits all. Simply changing the crossfeed settings, like a lens in focus, cured the blurry sonic image that showed up in the T10 during critical listening. Now pin point sharp, and laser sharp, once I changed to more optimal crossfeed settings.
Just crossed into the new year - 2025.
In conclusion, I'm learning how to squeeze more out of each product, and think this is where effort should be made. Yes buy a decent, well designed and manufactured product as a starring point, but with EQ, The right eartips, and the other points raised above..
11. There is a potential for mismatch in the IEM, which is caused by poor design or poor Quality Control @ manufacture. Combined with inconsistencies in our own hearing, between left and right ears - such as canal length and shape differences, so much opportunity to get a wrong impression of what one is hearing, cos of the imbalance. Have learned how to use placement, i.e slightly different insertion depths to address this issue., combined with software adjustment of the stereo image. These are differences one does not notice as much on headphones, and may never notice on speakers.!
12. All this "retuning" in software takes time. One cannot get anywhere with a rushed attempt. But the end result is well worth the effort.