Could you link me a good intro article for a non-engineer? amazing , thanks again.
Unfortunately I don't know any.
What you see here basic frequency response graph uncompensated - meaning that's just raw measurement of frequency.
Typical cues to look for: (all in relation to 1kHz)
Bass (0-250Hz)
-3-5dB - fast/super-accurate, very flat
0db - flat
+3dB - slightly warm, natural
+3-6dB - warmish, natural
+6-10dB and more - bass heavy
Upper mids/lower highs (1,5-3,5Khz)
-3dB - dark, cloudy
0dB - cloudy
+5dB - smoothed out, warmish
+10-12dB - natural, energetic, vivid
Highs
5-7kHz range = sibilance region, but sibilance is more related to CSD rather than normal graph, so it's not so easy to judge
10kHz = presence region - peaks here are typically responsible for clean sound, clarity, separation, resolution
10kHz+ region typically only gives you an idea how far highs extend
Hope this helps you a bit.
[Edit] in case of SD-2 its bass is not very flat though. It sounds very natural to my ears. Sometimes simple graphs can show you only small part of how the IEM sounds, much more tells CSD graph.