I am a firm believer in EQ. Thanks to
PiccoloNamek's EQ guide, and with
some inventions of my own, these days I can spend less than an hour with just about any new pair of IEMs and tweak them to sound better than anything I've heard without EQ, at any price. (and I've heard up to $400 IEMs) The main reason for this easy improvement is that I can use EQ to tame half-wave resonances, as explained for example by Siegfried Linkwitz, who's responsible for a lot of loudspeaker inventions:
http://www.linkwitzlab.com/reference_earphones.htm
A side product of this is that I can profile the frequency response of the phones much like a spectrum analyzer, but with my own ears. A raw FR chart coming from e.g. headroom often looks like a stock market chart on Black Friday in the treble frequencies, because of resonances. It is hard to translate such a graph into actual listening impressions. The smoothed and compensated graph is easier to read but smoothes out some of the important resonance frequencies. I believe my "FR charts" provide a happy medium: they show the main resonances in an easy-to-read chart, backed by the impressions of a human listener. They also have the advantage of not requiring any measurement equipment that I don't have
The FR charts are, greatly simplified, generated by feeding sine tones through an equal-loudness compensation EQ filter that mimics the frequency response of the human ear listening to an external sound source placed in front, then I tune a second EQ filter until I hear a flat FR. I then tune the EQ some more by listening to actual music, then the EQ is inverted to provide a frequency response graph of sorts compared to the ideal frequency response for my ears. (My own sound signature preference can be characterized as a W sound sig, with prominent mids, scooped out midbass to provide clarity to the rest of the spectrum (the opposite of what's usually termed a "warm" signature) and recessed highs at the sibilant frequencies to avoid sibilance)
Sound score will be on a 0-10 scale for unEQed sound and 10-20 scale for EQed sound, to reflect the fact that just about the worst EQed sound I've ever heard on any "proper" IEM (from any trustworthy brand, that can be bought for $10 and up) sounds better than the best unEQed sound I've heard at any price.
LIST OF REVIEWS TO DATE
(Prelude) Etymotic MC2/3/5
(C1) TDK Clef-P, vocal tune edition, $32
(C2) Panasonic Ergofit RP-HJE120, $7
(C3) Philips SHE3580, $10
(C4) Sony MH1C
... More reviews will be coming out soon
While you're waiting, here's a compilation of almost all the frequency response graphs I've made to date, all referenced against the original $10 headphones that could for me, the Philips SHE3580: