The ER4XR is a high-performing in-ear monitor with a single balanced armature (BA) driver, making it highly accurate and compact. The anodized aluminum shells are CNC machined with tight tolerances and are paired with a durable, replaceable cable. Known for its strong passive isolation, the ER4XR offers 35-42 dB of noise reduction, making it ideal for audiophiles who seek an immersive audio experience. The right and left channels are matched within 1dB across frequencies, providing a consistent and enjoyable listening experience. The ER4XR offers a "fun" sound signature with added bass compared to the reference model, ER4SR. ER4SR is ideal for sound engineers and audiophiles who prefer a flat and accurate sound reproduction, while ER4XR is for those who enjoy a bit of added bass presence. The frequency response graphs are designed to deliver a perceptibly flat frequency response that compensates for the resonance in the ear canal. The target frequency response was developed by Etymotic based on over 20 years of human hearing and acoustics research. Each ER4SR and ER4XR comes with a channel-matching compliance graph.