ER1 by Etymotic Research was designed to imitate the normal resonance of the open ear, and is used for speech audiometry where the goal is to reproduce the same frequency response at the eardrum for speech as would be produced in the live situation.
ER3C™ earphones are the next generation of insert earphones, replacing ER3A earphones, which have been the worldwide standard for audiometric insert earphones since 1985. 10 Ohm or 50 Ohm model available.