Have been using my SHE3580s for a bit since I've gotten them now, and I think they've been at least burned in enough (60 or so hours of use). Appreciated the recommendations about the tight seal with these earphones, for that did improve the sound quality noticeably. Though it seems these earphones in general are difficult to adjust and seal (at least compared to my old 630s). Tried out all 3 sizes and even with Medium being the best fit, it takes a bit of wriggling to get them to settle in properly.
The issues with the headphone jack have relatively cleared up since initial use. Haven't really heard the channels go out when I twist around the jack anymore. I do not have the mic model, just the standard earphone model, so no issues about bad connection because of TRRS incompatibility here.
As for the sound... my impressions of the SHE3580 have changed, but not necessarily in terms of better or worse. One thing I emphasized previously and have come to appreciate even more with use is the resolution of the earphones. The level of detail and clarity I have been hearing out of these, from the mid-background instrumentals, back vocals, and the like, have been a real treat, since I had never expected to ever have such resolution on cheap earphones.
However, I still have issues with the bass, in light of what's been said about these here. After listening with a proper seal, I can definitely appreciate the bass much better than with initial use. But it seems, to me, that while the SHE3580s are really good at letting you
perceive the bass, it is weak at actually letting the listener
feel the bass. For the songs I listen to, I can certainly hear the lowest bass and beats, but it is a completely clinical feelings. There is no
energy out of the bass levels at all, which diminishes the pleasure of many songs when you can hear how low the bass guitar or synthesizer beat is going off, appreciate the lower registers, but are completely unmoved by it because of the lack of "oomph."
And on another note, EQ is completely necessary with these earphones. After tuning the EQ to a curve similar to what Joe Bloggs has suggested, there was a
very noticeable change in dynamics. EQing complement these earphones
extremely well, and can definitely make up for the dynamic shortcomings inherent with these earphones. This is a sample of my EQ settings (adjusted for increased bass, as per my personal tastes, but not at all necessary to see the improvement that EQ can give to these earphones):
During my commutes I've been switching on and off between using EQ to non-EQ, and the difference in dynamics are great enough for me that it's pretty much gotten to the point that I won't stand how weak and unpronounced the stock sound is and always have the EQ on when using these earphones.
All in all, these earphones are an interesting buy, but they weren't the well-rounded super-bargain earphones that I was hoping for. Doesn't mean I still won't keep and use them though.