ER3XR lives up to the Etymotic legacy
I have been a fan of Etymotic gear since I bought my first ER4 many years ago. Clarity, purity, and intense detail are hallmarks of this brand, and I know of no other IEM that approaches the Etymotics in this area. The ERs reveal detail in recordings that surprise, astonish, and reward the listener, and I can always rely on them to present information in my recordings that I never knew was there. The old ER4 is a champ in that regard, and the ER3XR has 90% of that capability. However, while there is a small tradeoff from the ER4s in that crystaline presentation of mids and highs, and a bit less sense of space and air between instruments and notes, the ER3XR rewards the listener with a richer, deeper bass that is missing in the ER4.
When I use my ER4, I often boost the bass so that it has a more balanced presence. The ER3XR, on the other hand has that already, along with another octave or two of low-end oomph that equalization alone cannot provide. I welcome that tradeoff in certain genres and recordings, where pace and rhythm benefit from a robust foundation and a wide frequency range in music reproduction.
I also own a pair of the ER2XR, which is similar to the 3, but with a noticeably lower amount of secret sauce. Bass in the 3s sounds subtler because it is more controlled and better refined. Mids and highs have that Etymotic magic, to a greater degree than the 2s. The difference between the 2s and the 3s is much more substantial than the difference between the 3s and the 4s. In the latter case, the bass boost is the obvious standout, with the slight reduction in detail that I mentioned earlier, that may not even be obvious without a direct comparison to the various versions of the ER4. So, with the ER3XR, you get a big slice of the Etymotic pie with a substantially smaller price tag.
Like all Etymotic IEMs, these perform best with deep insertion in the ear canal, and some will find that uncomfortable. I find that the grey foam tips work the best for me. I also have used pro ear tips from Comply that aid in both achieving the necessary insertion depth and creating the exceptional isolation these provide (think "noise reduction"). If ample bass and magical mids and highs are what you crave, I suggest trying Comply tips with the ERs. However, the range of tips that come with the ER3XR provides many options for finding a balance between comfort and the isolation that is necessary to get the bass performance that these guys can provide.
These newer ERs also have a better cable (much less microphonic) and cable management that the old ER4, which makes using them yet more satisfying. I still return to the ER4 when I want to mine the most information from the recording, but the ER3XR is not far behind, and is now my go-to when traveling or just looking to disappear into the music with delivery by IEMs. They have excellent isolation (great for air travel), unrivaled detail, and now greater pace, rhythm, and timing enhanced by clean, clear low frequencies. They are not bass-heavy, though - look elsewhere for head-banging bass if that is what you crave. But for a satisfying balance in music and the opportunity to discover hidden gems in your recordings, the ER3XRs are a great choice at a very reasonable price.