The aim of this study is to investigate the effects of ear drum perforation
on real-ear to coupler difference (RECD) in adults. RECD was measured usin
g a probe tube microphone system in 22 patients with ear drum perforations.
Twenty-two normal subjects served as controls. For normal subjects, RECD w
as in good agreement with the values reported in the literature. For the pe
rforated ears, the RECD was up to 8 dB smaller in the frequency range from
0.5 to 1 kHz. There was no significant difference at frequencies below 0.25
kHz and above 1 kHz. A much larger intersubject variability was found in t
he experimental group. The mean intersubject standard deviation was 4.4 dB
in the experimental group as contrasted with 2.2 dB in the control group. N
either the equivalent ear canal volume nor the perforation size appeared to
be correlated with the degree of RECD reduction over lower frequencies. Th
ese results strongly suggest the need for individual RECD measurements, rat
her than using the average normal RECD, to appropriately compensate for the
reduced transmission of lower-frequency sounds in fitting hearing aids for
patients with ear drum perforations.