Several considerations are given to insertion gains measured by body aids under different measuring conditions. Measurment was carried out as follows: (1) Simulated insertion gain was measured when a body aid is placed in a pocket of a man's jacket and also when the aid is set away from the jacket at intervals of 10cm toward a loudspeaker. (2) Two types of body aids were tested. Apertures of microphone in these aids were set in two different ways. MODEL (A): The aperture faces both the upper side and the front of the aid. MODEL (B): The aperture faces only the upper side of the aid. (3) Simulated insertion gains were measured by SAMRAI with C-coupler. (4) A microphone which has a special aperture was also tested. The structure of the microphone is equivalent to a hearing aid whose aperture faces the front. From these measurements, it was certain that MODEL (A) is less affected by the difference of measuring conditions than MODEL (B). And the similar result to MODEL (A) is obtained from the microphone mentioned in (4). As a result, it would be advised that a substantial aperture of a microphone for a body aid should face the front.
The most suitable saturation-sound-pressure-level (SSPL) of hearing aids for moderate hearing loss was studied in 341 cases. They consisted of 253 cases of sensorineural loss, 45 of mixed loss and 43 of conductive loss. The selection and adjustment of the hearing aids were performed in hearing aid clinic at our hospital. In the cases with sensorineural loss, the mean value of the optimal 90dB SSPL were about 105dB in cases of 45-55dB HL, and 110dB in cases of 60-75dB HL. In spite of a small difference between the groups of different hearing levels, individual variations were large within the groups of the same hearing levels. There was no difference of optimal SSPL between the types of hearing aid, and between the cases with different audiograms. In the cases with conductive and mixed hearing losses, the mean of the optimal 90dB SSPL were about 5dB higher than those of the sensorineural loss at each hearing level. The results provide useful data for the selection of hearing aid and the adjustment of SSPL to an individual case.
The MCL level is an important index in the hearing aid evaluation. The aims of this research are to investigate where the MCL level is located in each subject's dynamic range and whether it could be predicted based on the measured dynamic range. The results were as follows; (1) Mean values of MCL levels in each frequency were near the 2/3 point above the minimum auditory level in the dynamic range in subjects with normal hearing and conductive hearing loss. In subjects with sensorineural hearing loss, however, the measured level of MCL showed a tendency to be lower in their dynamic range in the high frequency range; intersubject variability between the measured MCL level and predicted value based on the dynamic range was large. This suggests that the direct measurement of MCL is important, especially in patients with sensorineural hearing loss. (2) In subjects with normal hearing, average MCL level contour nearly fell upon their average equal loudness contour. (3) In subjects with normal hearing, the MCL levels measured by pure-tone stimuli agreed roughly with those measured by filtered speech stimuli not in 50% level (L50) but in upper 90% level (L5).
The suitable acoustic gain and frequency response of a hearing aid in noise were studied in seven individuals with moderate sensorineural hearing loss. The test sounds consisted of a 57-word list mixed with three kinds of noises. Most comfortable loudness levels and speech discrimination scores were obtained corresponding to the different frequency responses of the hearing aid. The results were summarized as follows. The acoustic gain of a hearing aid should be adjusted to the MCL, for adapting to a surrounding noise and its frequency response. Regardless of the kinds of the surrounding noises, the suitable frequency response of a hearing aid is commonly one with a low-frequency cut-off slope of 6-12dB/octave. It is to be desired that, if the frequency distribution of the surrounding noise which an individual encounters in daily life is estimated, the frequency response of a hearing aid in the individual case is appropriately adjusted in order to adapt to the surrounding noise and to improve the intelligibility of consonants.
The purpose of this study is to evaluate the effects of hearing-aid performance on Japanese monosyllabic discrimination scores in noise. The subjects were 10 adults with mild to moderate sensorineural hearing loss. A 50-item monosyllabic discrimination test was administered repeatedly with the use of three behind-the-ear type hearing aids with different frequency-gain characteristics. Speech spectrum noise was applied as a competing noise at the S/N ratio of +10dB. Main results were as follows: 1) Regarding to the group data, mean percentage correct of monosyllabic discrimination scores did not show significant differences among the three hearing aids. 2) The individual data showed that three of the subjects made significantly higher discrimination scores with the broad-band flat amplification characteristics. 3) For the discrimination of voiceless consonants in noise, the high-pass filtering type amplification and also the broad-band flat type amplification were significantly effective. 4) For the discrimination of voiced consonants in noise, the high-pass filtering type of amplification was significantly inferior to others. 5) The subjective evaluation of the hearing aids consistently showed that the broad-band flat type amplification was evaluated as “the easiest to listen” and the high-pass filtering type amplification “the uneasiest to listen”.
Sound quality perceived through a hearing aid was investigated by factor analysis to find out dimensions in perceived sound quality and to explore their relation to electroacoustic characteristics of the hearing aid. Sixteen cases with moderate and moderately severe sensorineural hearing losses were studied. They judged quality of test sounds perceived through the hearing aid under 27 different electroacoustic conditions (3 saturation sound pressure levels×3 frequency response characteristics ×3 acoustic gains). The test sounds consisted of various kinds of speech and daily life sounds. Results were summerized as follows; (1) By means of factor analysis of sound quality, four dimensions were obtained, and the dimensions were interpreted as factors of ‘fullness’, ‘calmness’, ‘distinctness’ and ‘true to nature’; (2) Adjustments of either the SSPL or the acoustic gain had relation with each of four factors; (3) Adjustments of the frequency response related only to the factor of ‘distinctness’; (4) Grade of harmonic distortion, related mainly to the factor of ‘distinctness’. These results are very useful for fitting hearing aids to cases with sensorineural hearing losses.
The electroacoustical characteristics of hearing aid measured in a 2cc coupler are not directly applicable to psychoacoustical real-ear function for prescription of the necessary gain and frequency response of an optimal hearing-aid. In this method loudness measurements were entirely made through a cearing-aid in a listener's ear in account of functional gain. And the most comfortable sensation levels (MCSL) and the uncomfortable sensation level (UCSL), that could not be predicted by the thresholds of severely hearing-impairred individuals, were obtained with 1/3oct. band noise uning the aided audible field measurement. The desired gains of hearing aids were computed prescribed as those that placed in the assumed aided speech spectrum within the listener's dynamic ranbe of hearing in a normal and comfortable pattern.