Using the FONIX 7000 to Verify Coupler and Real-Ear Performance ...

Real Ear Measurements 28
Figure 33 – Illustrating the importance of the correct placement of the probe tube (Dirks
and Kincaid, 1987). Think of the abscissa as the length of the ear canal (3.0 cm = 30
mm) and what happens to measured SPL near the TM as the probe tube is placed
along this line. For
example, at 2000 Hz
the measured SPL
@ 30 mm from the
TM is ~ 2 dB less
than measured at
the TM! Thus, for
2000 Hz and below
the meaured SPL
would be essentially
the same regardless
of where the probe
tube is placed along
the ear canal. On
the other hand, @ 8000, if the clinician placed the end of the probe tube ~12 mm from
the TM, the measured SPL would be ~ 12 dB less than what is present at the TM. The
other curves @ 3000-7000 Hz reveal similar findings.
Figure 34 – Illustrating the proper placement of the probe tube in the ear canal where
the measured REUG @ 6000 Hz is @ 0 dB gain. This is another method to verify that
the probe tube is in its proper place along the ear canal.