[In situ measurements for determining the effect of additional boring of the earmold]

To investigate the effect of earmould venting on the insertion gain of hearing aids in patients' ear canal, the authors sealed 35 earmould ventings with soft silicone after measurement under normal conditions and repeated the measurement. The size of the ventings varied from 0.8 mm to 3.5 mm in diameter. The results show the expected SPL-reducing effect of the ventings between 500 Hz and 1,000 Hz. Below 500 Hz the effect found was only slight, because of the low amplification in this frequency range. Above 1 kHz an increasing sound pressure level was measured as a result of resonance effects. This study illustrates the effect of earmould venting on insertion gain. To improve the hearing aid fitting the earmould venting should be used, deliberately and specifically, far more often than at present. The resulting effects of earmould modifications of real ear gain can only be determined by in situ measurements on the patient's eardrum. This method also enables resonance to be compensationed for in a controlled manner.