Improved methods to diagnose a hearing loss and the enormous progress
in the development of digital and programmable hearing aids have been
helpful in promoting the social integration of patients, even of those
affected by a profound deafness. Besides the hearing loss, recruitmen
t effects and alteration of sound can also be compensated by the new h
earing aids. However, one precondition is that the hearing aid fitting
is carried out professionally, with plenty of time, and including the
new hearing aid fitting methods. The new techniques developed in our
hospital to optimize hearing aid fitting are pointed out. Fitting shou
ld start by considering what kind of ear mould and what kind of differ
ent modifications are to be taken. In a great number of patients we we
re able to verify that venting combined with the insertion of a Bakke-
or Libby-horn increases not only the subjective acceptance of the hea
ring aid, but also significantly improves speech discrimination, parti
cularly under background noise. The preselection of the hearing device
and precise adjustment are based on the hearing loss in different fre
quencies, involving the principle that the frequency response of the h
earing aid and the audiogram mirror each other accordingly, whereas th
e gain of the hearing aid can not be recognised exactly from the audio
gram. In contrast to the POGO- and the NAL-method, we recommend a grea
ter amplification, especially in the higher range of frequency. Today,
the in-situ-measurement with a probe microphone is considered to be t
he method of choice for accurate frequency adjustment. This in-situ-me
asurement allows an exact determination of the frequency response of a
hearing aid and enables to perceive unpredictable resonance effects i
n the external ear canal. This is of particular importance when checki
ng the hearing devices of children who have a significantly altered ex
ternal ear resonance. When evaluating the speech discrimination in the
presence of background noise, it is necessary to use different noises
. We could determine that the masking effects were very different, whe
n speech-noise, Doring noise and Fastl noise were used. For the accura
te adjustment of hearing devices, we also have to take into account th
e dynamic range. Comparative measurements show that the determination
of the uncomfortable loudness level with monosyllables is absolutely i
nsufficient, particularly when new multichannel hearing aids are fitte
d. The uncomfortable loudness level for narrow band noise and sinus to
nes is frequency-dependent and differ from the UCL of monosyllables. L
ikewise, for adjusting the PC and AGC, the in-situ-measurement has tur
ned out to be reliable, because the hearing aid characteristics in the
protocols of the hearing aid companies show big differences, because
they are measured with a 2 cm(3)-coupler. As before, the reliability o
f the otometry to verify the range of comfortable hearing has been est
ablished. In case the adjustment of a hearing aid is especially diffic
ult, the temporal resolution should be taken into account. We were abl
e to verify in a great number of patients that the temporal resolution
of the hearing can improve or deteriorate by fitting a hearing aid. I
f a suitable hearing aid is used, an improvement in the temporal resol
ution capacity proceeds with an increased subjective acceptance of the
hearing aid and usually, with an improved speech discrimination under
background noise.