Over 30 years ago, Etymotic invented noise-isolating, in-ear earphones. Etymotic's original design, developed for auditory research and hearing testing, used balanced - armature receivers and established these speakers as the gold standard for high-definition, in-ear earphones. ER4 earphones were the first high-fidelity, noise isolating in-ear earphones to use this technology in a consumer earphone, and are recognized as the world leader for response accuracy to which all other earphones are compared.