ABSTRACT
A new power behind-the-ear hearing instrument with digital feedback suppression (DFS) seems to be an important step towards solving the problems of acoustic feedback in high power instrument fittings. Previous experiences (Dyrlund & Bisgaard, 1991) with a DFS prototype are confirmed in the present work. Ten profoundly hearing-impaired children were fitted with the new DFS instrument and wore it over a trial period of approximately three weeks. with the new instruments the rationale was to supply equivalent low frequency (< 1 kHz) gain compared to the subjects' original hearing instruments, and extra 5-10 dB high frequency (> 1 kHz) gain. The hypothesis was that with the new DFS system it would be possible to provide extra high frequency gain for these children without the annoyance of acoustic feedback. The test included questionnaires before and after the trial period, comparative free-field audiometry between the subjects' original and DFS instruments. The free-field audiometric results show a typical improvement of 5-10 dB at 2000 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 period, and was generally preferred by 9 of the 10 subjects after the trial period.
Subject(s)
Feedback , Hearing Disorders/diagnosis , Adolescent , Audiometry , Auditory Threshold , Child , Female , Functional Laterality , Humans , Male , Surveys and QuestionnairesABSTRACT
The introduction of a new power behind-the-ear hearing instrument equipped with an integrated digital feedback suppression (DFS) system, based on adaptive, digital signal processing, creates the need for new methods for evaluating the characteristics of this new technology. A special measuring method based on determination of the complex loop gain of the DFS instrument and the associated feedback path is described. This method yields information about the static feedback-margin improvement due to the DFS system, and the method is usable especially in connection with measurements on real ears. It requires fairly advanced test facilities, including a dual-channel FFT analyzer and, by preference, an anechoic room. Loop gain measurements on the new DFS power behind-the-ear hearing instrument show encouraging results. Groups of profoundly hearing-impaired children and adults were tested, and static feedback-margin improvements in the order of 10 dB for the new DFS power hearing instrument were seen. Variations were largest for groups using own ear moulds and individually fitted instruments.
