Etymotic needs no introduction when it comes to IEMs. They were around during the early days (before most of you kids in 2022 obtained sentience) and a proponent of their "diffuse field" target. The ER-4S, pictured below, can arguably be called the HD600 of the IEM world. If you didn't own one, you at least heard one, most likely being able to borrow a friend's ER4S for an extended period of the time. ER-4S with triple flange deep penetrator tips. The ER-4S was finicky. Most complaints revolved around it sounding too thin, having too much emphasis around the pinna gain region 2-3kHz, and having a small spike in the treble. The secret to using the ER-4S was super deep insertion, usually with the treble flange penetrator tips. Naturally, most people did not like the feeling of having their ear holes penetrated so deeply. Now what seems like 15 or more years later, the folks at Drop have collaborated with Etymotic to make a new version called the ERX for people who did not want their ear holes assaulted. There's now a normal IEM body instead of a phallic tube. In addition, a set of tips is included that provides a good seal with a good tonal signature (that is not lean or spiky in the highs). At least for me it did. FWIW, I did try the triple flange tip and could not get it to work properly because the body of the IEM prevents deep insertion. Anyway, why did it take so long? Drop + Etymotic ERX IEM I would have to say that this is the most agreeable Ety yet to my ears. There's a good amount of bass that extends low. It's not overdone. Of course tastes and gear references vary, thus I can see many IEM users wanting moar bass, moar upper-mids, more treble, a la the Harmon Curve, which this community on average happens to somewhat disagree with (or vehemently disagree when comes to its IE target). It would say, take the stock ER-4S tuning, lift the bass a bit, lower the highs a bit, and keep the 2-3kHz bump. The 2-3kHz bump is slightly too much for my ears, probably because my pinna amplify this region more than what Ety expected. IEMs bypass pinna, so inverse HRTF curves will never be perfect. However, things were not so far off that I wasn't able to acclimate after a few songs.