**Q**: There are so many terms related to wideband acoustic immittance, MEPA, and reflectance that I get confused. Can you set me straight?

**A**: We agree, it is very confusing! The method of wideband middle-ear power analysis and it's related quantities, such as wideband reflectance, are called by many different names in the literature. Here is an attempt to disambiguate the various terms. See your MEPA manual for more indepth information about these quantities.

Acronym or Symbol | Term | Disambiguation |
---|---|---|

MEPA | middle-ear power analysis | Broad term encompassing the measurement of power reflectance, admittance, and impedance quantities. |

acoustic power assessment | As for MEPA | |

immitance, wideband immitance | Broad term encompassing wideband immitance measurements, including MEPA, acoustic reflexes, and tympanometry (any test using a probe to infer middle-ear status) | |

RMS | reflectance measurement system | As for MEPA |

WAI | wideband acoustic immittance | The 2013 Eriksholm Workshop on "Wideband Absorbance Measures of the Middle Ear" produced a consensus statement recommending the term Wideband Acoustic Immittance to refer to the family of wideband measures, including power-based and impedance-based measures such as reflectance and absorbance. |

WB ATF | wideband acoustic transfer functions | Includes reflectance and admittance quantities |

WMEP | wideband middle ear power | As for MEPA |

wbMEPA | wideband middle-ear power analysis | As for MEPA |

Acronym or Symbol | Term | Disambiguation |
---|---|---|

CAR | complex acoustic reflectance | CAR is equal to the ratio of the reﬂected to incident wave pressure at the microphone, located in the ear canal, as a function of frequency, in complex notation (magnitude and phase). The magnitude squared CAR is Reflectance. |

EA | absorbance, energy absorbance, power absorbance | Power absorbed; aka Transmittance, Absorption. Complement of power reflected. Has the unit proportion, or percentage, or decibel, relative to 100% power absorbed |

1-|R^{2}| |
absorption, power absorption | Power absorbed; aka Absorbance, Transmittance. Complement of power reflected. Has the unit of proportion or percentage, relative to 100% power absorbed. |

ECR | ear-canal reflectance | As for Reflectance. |

ER | energy reflectance | As for Reflectance.* |

R, |R^{2}| |
reflectance; power reflectance; reflectance magnitude | Has the unit of proportion, or percentage, relative to 100% power reflected.* |

transmittance; power transmittance | Power absorbed; aka Absorbance. Has the unit decibel relative to 100% power absorbed. | |

WBR | wideband reflectance | As for Reflectance. |

* Energy is a static quantity. Power is energy flow, defined as the energy per unit time. Specifically energy is in Joules and power is in Watts, which is Joules/sec. Energy flows in and out, giving rise to a power. Since MEPA measures the flow of energy, it seems more logical to call MEPA a Power-reflectance rather than an Energy-reflectance, which was the term used in much of the earlier literature. Today the preferred term is "Power reflectance" over "Energy Reflectance."

Admittance (Y) and impedance (Z) are complex numbers, and are reciprocals (Y=1/Z and Z=1/Y).

Acronym or Symbol | Term | Disambiguation |
---|---|---|

admittance; wideband middle ear admittance | Broad term encompassing admittance magnitude, phase, conductance, and susceptance quantities (see impedance for reciprocal terms) | |

Y, |Y| | admittance magntidue | Magnitude of complex admittance |

Re(Y) | conductance | Real part of complex admittance |

impedance; wideband middle ear impedance | Broad term encompassing impedance magnitude, phase, resistance, and reactance quantities (see admittance for reciprocal terms) | |

Z, |Z| | impedance magntidue | Magnitude of complex impedance |

Im(Z) | reactance | Imaginery part of complex impedence |

Re(Z) | resistance | Real part of complex impedance |

Im(Y) | susceptance | Imaginery part of complex admittance |