This interdisciplinary long-term study examined the effects of recreational noise exposure on the hearing of adolescents. Boys and girls (aged 14-17 years) were examined during a four-year period. Audiological, psychosocial, and sound measurements were performed yearly to determine the hearing threshold level (HTL) of participants in the 250-16000 Hz range, their participation in recreational activities, and the sound levels at discos and through personal music player use. A tendency of the mean HTL to increase in both genders during the study was observed, especially at 14000 Hz and 16000 Hz. Boys had a higher mean HTL than girls. The participation in musical activities increased yearly, 'attendance at discos' being the favourite musical activity for both groups. In general, boys were more exposed to high sound levels than girls. The equivalent sound levels in discos ranged between 104.3 and 112.4 dBA, and between 75 and 105 dBA from personal music players.
Intended as an input to international standardisation, this study investigated reference hearing thresholds for the calibration of audiometric equipment, which have been determined using 'clicks' as test signals, several kinds of earphones, and two types of transducers (a loudspeaker and a bone vibrator). The threshold measurements were carried out with groups of 25 test persons with normal hearing capability following as far as possible the ISO-preferred test conditions. The influence of different parameters on the results, such as click duration, polarisation mode, repetition rate, gender and age of the test persons, or type of ear simulator, was studied. The results mainly depend on the type of ear simulator used to calibrate corresponding audiometers. Together with the results of another investigation carried out in Denmark, the data of the present study shall form the basis for the coming International Standard ISO 389-6 on reference hearing thresholds for acoustic test signals of short duration.
Threshold measurements with a Präcitronic KH 70 bone vibrator were carried out on 25 young, otologically normal subjects (50 ears) in the frequency range between 125 Hz and 8 000 Hz. The vibrator was applied to the human mastoid as well as to the forehead. The non-test ear was masked. Equivalent threshold force levels were determined on an artificial mastoid type B & K 4930. Between 125 Hz and 2 000 Hz, the equivalent threshold force levels for mastoid placement decrease steadily by about 13.5 dB/octave, they then increase again by about 10 dB and remain constant between 4 000 Hz and 8 000 Hz. The equivalent threshold force levels for forehead application were found to be higher by about 11 dB in the whole frequency range.
The aim of this study was to determine reference peak-to-peak threshold sound pressure levels for air conduction sound transducers using groups of tone bursts as test signals. For this purpose, threshold measurements with five different earphones and a loudspeaker were carried out on groups of 25 young, otologically normal test subjects in the frequency range between 250 Hz and 8000 Hz, following as closely as possible the ISO Preferred Test Conditions. The dependence of the results on repetition rate, type of sound transducer, gender and age of the test subjects, and on reference pure tone thresholds was investigated. The results mainly depend on the reference equivalent sound pressure levels for pure tones of each sound transducer. Together with the results of another study carried out in Denmark, the data of the present study will form the basis for the International Standard ISO 389 Part 6 on reference hearing thresholds for acoustic test signals of short duration.
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