Question
In practice we sometimes bump into the binaural Hearing Aid fitting with the instruments of different technologies. I mean the situation when patient is fitted with analog (classic) instrument on one ear and with digital one on another ear. In most occasions we have binaural balance problems with such patients. Please let us know your opinion on this matter. Do you know what digital instruments are compatible with analog ones for binaural fitting.
Answer
We have long known that there is a binaural summation effect in the presence of normal hearing: binaural stimulation is perceived at a combined greater loudness than monaural stimulation of the same SPL. In normal hearing ears, this summation effect can be as great as 6 dB. However, the picture is a little more clouded in the presence of sensorineural hearing impairment. The actual summation effect is more variable, and usually measured to be a little less than the normal ear. However, a binaural set of hearing aids probably can be worn at slightly lower volume control setting than individually fit monaural aids.
In fact, in earlier versions of our fitting software, we calculated our prescribed gain based on an assumed monaural fitting and then dropped the gain by 3 dB in the case of a binaural fitting. In more recent years, we have assumed binaural fiings. (Shouldn't we all?) If the patient is fit monaurally, we reccommend a increase of a few dB, if the patient reports the overall loudness as too soft. In the case of a mixed fitting (for example, linear in one ear and nonlinear in the other or an assymetrical hearing loss), it becomes hard to predict. Therfore, we reccommend that the clinician manage this issue post fitting: as part of the fine-tuning process, a binaural loudness balance check should be included.
Bio.
Donald J. Schum, Ph.D./CCC-A
Vice President, Audiology & Professional Relations
Oticon, Inc.
29 Schoolhouse Road
Somerset, NJ 08873
1-800-227-3921 (ext. 535)
DJS@Oticonus.com
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