before going to war because somebody suggests that some DSP or even just competent EQ can make cheap stuff sound great, I would like to list a few ideas which are usually accepted as factual:
1/ it is very difficult to EQ accurately by ear. it's sort of a job actually.
I spent almost 2 entire years trying again and again with test tones and sweeps to gain experience, and be able to tell what frequency wasn't right and how much was the right compensation. it's long, hard, and even then the result will probably be in the +/-0.5dB in the midrange, it can still be up to several dB at both ends of our hearing. at least that's the case for me.
2/ if I put 2 IEMs in my microphone and make an EQ to compensate the difference, that would be the right compensation for my coupler and the way the IEMs went in it. which is almost certainly not how they would be in my ears. meaning some resonances wouldn't be where I measured them so the FR would not be the same. I actually try to address that when I do my own measurements, as EQing my stuff easily is 95% of why I even own a mic and a coupler. but in the end I still have to rely on a all lot of subjectivity and tuning by ear. so back to 1/
3/ most people with some serious experience in acoustic and listening tests will tend to agree that the frequency response is the dominant variable when it comes subjective impressions and preferences.
many audiophiles imagine that stuff like clarity, soundstage, or how "fast" the bass is, won't be related to FR and must have some other more important causes like transient whatever and distortions. and while those are some of the possible causes, they will come in play if and only if they happen to be very bad(like madly underdamped driver or above 1% THD). basically they make audible differences if they cause audible issues(thank you captain obvious!!!). so I'm not saying to forget everything and assume that a FR tells us everything, because of course that's super dumb. but there is really no reason to act surprised or revolted when someone proposes that another IEM with a similar signature might be just as pleasing and very similar all around. nobody claimed it would be identical in every way, so those who try to introduce that "all or nothing" battle are just building a strawman argument. don't fall for that.
4/ in practice nobody who knows what he's doing would attempt to strictly EQ the upper treble. as many people can perceive those, it means that most EQ settings are not in fact going to fully copy the FR of another IEM(or heaphone).
78/(I use the numbers I want!!!) if one IEM had a terrible roll off of some massive dip, trying to EQ that back up to try and mimic some other IEM could fail and result in massive distortions while still not even reaching the right FR.
so all in all, even for partial EQ, it might not be given to everybody to do a great EQ job for oneself. as
@Joe Bloggs started before me, and kept going long after I felt satisfied and moved on to other stuff, I'm pretty confident that he can make some IEMs sound pretty good to his own ears with an EQ. those who visualize a dude turning 3 knobs and giving up, that's not Joe B at all. he's an actual mad man when it comes to DSPs and EQ in particular. ^_^
IMO, so long as distortions remain fairly low and phase doesn't imitate Tony Hawk in one of his games, chances are that the sound would come surprisingly close. but only if the FR we get to hear was actually the same. as to subjectively be fooled, that's an entirely different problem. sealed stuff and vented stuff don't feel the same, I'd just take a few steps or have a car pass by me and I'd know something is wrong. and of course with Ety, if I don't get brain probed by the IEM, I'm never going to believe I'm using an Ety! ^_^ so actually tricking someone into not knowing which IEM is which, that's a challenge way more difficult than just making a cheap IEM sound great or close to our own idea of neutral.
