DIGITAL FEEDBACK SUPPRESSION (DFS) - CLINICAL-EXPERIENCES WHEN FITTING A DFS HEARING INSTRUMENT ON CHILDREN

A new power behind-the-ear hearing instrument with digital feedback su ppression (DFS) seems to be an important step towards solving the prob lems of acoustic feedback in high power instrument fittings. Previous experiences (Dyrlund and Bisgaard, 1991) with a DFS prototype are conf irmed in the present work. Ten profoundly hearing-impaired children we re fitted with the new DFS instrument and wore it over a trial period of approximately three weeks. With the new instruments the rationale w as to supply equivalent low frequency (< 1 kHz) gain compared to the s ubjects' original hearing instruments, and extra 5-10 dB high frequenc y (> 1 kHz) gain. The hypothesis was that with the new DFS system it w ould be possible to provide extra high frequency gain for these childr en without the annoyance of acoustic feedback. The test included quest ionnaires before and after the trial period, comparative free-field au diometry between the subjects' original and DFS instruments. The free- field audiometric results show a typical improvement of 5-10 dB at 200 0 Hz and even larger improvements at higher frequencies. The increased high frequency gain provided by the new instruments did not give rise to significant complaints of feedback or howling during the trial per iod, and was generally preferred by 9 of the 10 subjects after the tri al period.