A quick synopsis of my resume. 30 years of hardcore interest and investment in hifi, instrument building, musician. I've owned many decades of home stereo equipment and have a definite preference and fondness for Vinyl.
The soundmagic e30 has been my only headphone in use for the last 1.5 years and they have proven non-fatiquing and thoroughly enjoyable.
Past headphones I've owned range from $1000 LCD, several $500-$200 of nearly every brand from the most current back through headphones from the 1980's and 90's.
Generally I have found many full size over the ear headphones disappointing and colored. Many have odd sound and/or a falsely exaggerated upper end clarity aspect that mimics high fidelity. I personally have spent (wasted) lots of money on these poorly designed headphones by companies who seemingly do not have a solid grasp on what instruments sound like in real life and so have no unwavering reference point to create musical and realistic gear.
Generally, I'd say the e30 is neutral/warm yet detailed with a pleasing full bodied sound and a moderate bass boost that varies depending on the particular pair (as I mentioned at start, individual headphones vary even within a particular model)
The e30 is 'hi-fidelity' in the sense that it imparts virtually no sound signature/sound stamp of its own onto your music collection with the exception of the already mentioned bass and also a modest and enjoyable lushness of the midrange of 2 of the 7 pair I own. Both those with this midrange lushness are the earlier run which feature a non twisted cable. You can still find the early run of this IEM by choosing less popular colors which have been sitting unsold on sellers shelves. The black sets will all be newer and twisted cabled but the blue pink and for some sellers, the white ones will likely be the early non twisted cables because they sell less quickly and so remain in sellers possession longer. This is good for us, since I feel they are a bit more special and musical than newer production e30's. That being said I enjoy 5 of the 7 sets I own with the other two a bit less balanced. The two I favor most are the non twisted cable. I do wish the bass was not exaggerated but many will actually find this a boon due to the popular bias towards a bit of a bass boost.
So the short story is: you can buy 3 sets of e30's for $100 and that is what i'd advise. That way you can have a bit of a choice and variation on a theme and you will likely find one or more a bit more special than the others. If you like a lush midrange, grab two of the older non twisted cable sets and one of the newer blacks and you'll be a happy listener.
The barrels are numbered. Whether that is a serial/production/batch number is unknown. the ranges of those in my possession range from M103 to m305. .
The older sets with non twisted cable have barrel numbers (M103 and M104 printed on the barrel). The other newer black (5 sets) have a braided cable. The smooth cable is from earlier in the production run from what I can gather and it sounds excellent. I am suspicious that twisting the cable increases the high end response in some way but at the expense of accuracy. I am unable to scientifically confirm this and it is a working theory. Either that or the earlier run of e30's had a bit different cone design or material composition either intentionally or unintentionally.
Whether the sound differences are from intentional production changes over time, from uncontrolled production variation, or from differing burn-in times is unknown but I'd wager it's a result of the last 2 phenomena.
addendum: this variation of sound within a model is not something I believe is unique to the e30 or soundmagic brand. I have experienced this fact with other models and suspect it is the case with all headphones.
They do need a solid overnight burn in with loud playing music for the bass to get in line and mellow.
Regarding fit. These are super comfortable and never fall out or irritate and come with two type of tip. One with a wide mouth opening and the other narrow. The narrow are definitely more appropriate and sound best. I would choose the narrow opening and largest size that will create a tight seal for your particular ears.
As of 10/14 I have purchased sets from this seller who still stocks the non twisted cable. Choose the blue or pinks or drop him a message and he will check and make sure you receive a non twisted cable set(s).