IEC TS 62886@ which is a Technical Specification@ describes a coupler and measurement methods to characterise the electroacoustic performance of hearing aids and insert earphones primarily in the range of 8 kHz to 16 kHz
TS 62886-2016 history
2016TS 62886-2016 Electroacoustics – Hearing aids – Method for measuring electroacoustic performance up to 16 kHz (Edition 1.0)