air pressure in an ear (or calibration cavity)

7.03  air pressure in an ear (or calibration cavity). Difference between the pressure of air within the external auditory canal (or in a calibration cavity) and atmospheric pressure at the location of the measurement. Unit, pascal (Pa).

Annotation 1      Air pressures observed in aural acoustic impedance and admittance measurements are conventionally reported in dekapascals (daPa). Traditionally, air pressure has been reported with respect to the height of a column of water it can support. At an air temperature of 20°C:

1 cm H₂O = 98.0665 Pa, thus

1 mm H₂O ≈ 9.81 Pa, or

1 mm H₂O ≈ 0.98 daPa, and

1 daPa ≈ 1.02 mm H₂O.

Annotation 2      Measured aural acoustic impedance or admittance may be affected by rate and direction of change of air pressure as well as by the amount of time the air pressure remains constant within the external auditory meatus.