ER4

ER4 is a line of in-ear monitors (IEMs) manufactured by Etymotic Research. First released in the 1990s, the ER4 family is noted for its emphasis on accurate, neutral sound reproduction and strong passive noise isolation. The design centers on a compact transducer housed in a metal body, coupled with a robust seal created by interchangeable ear tips to provide consistent performance across users and environments.

Variations in the ER4 lineup include the ER4S and ER4P. The ER4S is marketed for higher-impedance sources and professional or reference listening setups, while the ER4P is geared toward low-impedance, portable devices. The distinctions among these variants reflect different listening contexts rather than dramatic changes in overall sound signature, with the goal of maintaining a faithful, uncolored response.

Historically, the ER4 became a benchmark in in-ear monitoring for its isolation, fit, and measured accuracy, influencing later designs in the IEM genre. It has been used by audiophiles, broadcasters, and professionals seeking reliable isolation and reproducible sound when monitoring or evaluating audio. Over time, Etymotic expanded the lineage with related models and updates, but the ER4 remains representative of early efforts to combine high isolation with a reference-grade listening experience.