Advance warning: Long general rant ahead...
Just like speakers and the room, there are a few aspects to an IEM's sound and the interaction with the ear.
First - your ear itself. Can't change it. Hearing once lost cannot be restored. Shape of the canal allow a few to deeply insert IEMs while a few cannot as Anaxilus found out with purrin and DBA-02 (round peg in a square hole). Our ears exhibit higher sensitivity at certain frequencies. It's also not abnormal to have differently shaped ears and even in some cases, different dBs of hearing in L and R. So, the key is to know more about yourself.
Second - The tip used. The tips are the passage from the 'speakers' to the ear. So, different shapes of tips, their length, nozzle size, bore size and material all affect the final perceived SQ.
Third - is a combination of the two - the fit, the angle and depth of insertion possible. The interaction, in short.
Fourth - is the audio supply chain - the quality of source, distortion, recording, the loudness level you listen at, isolation, noise in the surrounding and so on.
Fifth and not often discussed - psychology and emotion. Our mood can play a big role without many of us realizing it. Placebo can be very influential. Our audio memory is often a blend of both sound quality and the satisfaction we derive out of it.
For instance, I still fondly remember the old Turntable in our home (restoring it will be a project sometime in the future). I still do not know if it's because it's just nostalgic
or I was least demanding at that time and just listening to music
or it was really
that good. About 3 years and a few '0000s in this hobby, I have still not derived the satisfaction I used to get when I was young. Is it because of SQ
or have I become that demanding with SQ? Even if I restore the TT, I do not have the old speakers that I listened them with, so guess I will never know.
When it comes to a review, one is not concerned about enjoying. It's always about comparisons. SPL match, run test tracks, do short A:B, do long A:B, X > Y in this and that, Y > X in that and this, rinse, repeat until you are ready to put that into words confidently. It's advantageous in one fact. When you do a direct A:B (same source, track, volume matched), you do not let your emotions come in the way (Even recently, I thought SHE3570 > ES18 before the comparison). On the other, it gets tiresome after a while as the process takes a bite of you. Secondly, not everybody is going to hear it the same way (all factors described above + music + signature preferences). That is why I am lucky to have ljokerl who likes certain aspects of sound which are important to me the same as me and dislikes a few things the same as me. It's not the 'same' all the way - no way, but I can safely bet that if he
personally loves a certain IEM, I am least likely to hate it and if he warns me about buying a certain IEM and I still go ahead and buy it, I will be disappointed. I have experienced both. The key to reading a review is always knowing what 'overlaps' you have with the reviewer's own preferences. It's not always one reviewer, but I look for certain descriptions from certain individuals. I also know where
not to look where the reviewer and I do not see eye to eye in sound descriptions for more than a couple of IEMs. All this took me a silent couple of years of reading in head-fi coupled with lot of buying. It need not even be a reviewer, sometimes people may not be familiar with audio jargon, but we can find their picks to be right for our ears. So, however you cut it, I think a lot of homework is required on our part too!
Just my usual 500+ word cent