ER3SE is a high-sensitivity single driver in-ear monitor (IEM) with a reputation for accuracy in audio reproduction. The IEM shells are made of anodized aluminum and are machined with tight tolerances to provide a compact design. The use of a single balanced armature (BA) driver allows for an easy-to-drive IEM with excellent accuracy. The ER3SE is also known for its impressive passive noise isolation, providing up to 42 dB of attenuation. This makes the ER3SE a popular choice for sound engineers, audiophiles, and budget-conscious consumers looking for in-ear monitors. ER3SE and ER3XR are the two ER3 models, both of which use the same high-sensitivity Balanced Armature driver that's easy to drive, even without an amplifier. The difference between the two is in the tuning of the lower frequencies. The ER3SE is designed to be neutral and flat, while the ER3XR is high-energy with emphasized bass. The ER3SE is a great choice for audio creators, musicians, and those who prefer to listen to music as it was recorded. The ER3XR is ideal for those who enjoy extra bass presence. Etymotic's goal is to have a flat frequency response curve that takes into account the resonance in the average ear canal. This results in a slight "hump" in the 2-5k region to compensate for the resonance and deliver a perceptibly flat frequency response. Etymotic's target frequency response graph is based on more than 20 years of research and expertise in human hearing and acoustics. In tuning IEMs, the goal is to accurately reproduce a live performance and factor in the acoustic properties of the ear. This requires a slight "hump" in the frequency response graph to compensate for the acoustic resonance and horn effects of the ear, which results in a flat frequency response perceived by the eardrum.