Etymotic ER4 XR & SR @ techPowerUp
 

Etymotic's ER4 in-ears set the benchmark when they were first launched over 25 years ago. Recently, Etymotic decided to bring out two new versions of their ER4 design - namely, the XR (Extended Response) and SR (Studio Reference). These new versions feature all-metal housings and a brand new cable design. On the acoustic side of things, you now get the choice between elevated bass and something that should be close to neutral in terms of the Studio Reference.

https://www.techpowerup.com/reviews/Etymotic/ER4XR_SR/