EAR MUFF PERFORMANCE DETERMINED BY THRESHOLD METHOD AND BY PROBE MICROPHONE METHOD

In connection with a European joint project regarding attenuation of i mpulsive sounds by hearing protectors an additional experiment was per formed on 16 subjects comparing the standardised subjective method (IS O 4869-1) with an objective method for assessing the attenuation of ea r muffs. For the objective method a probe microphone was used with a f rame supporting the microphone in the concha and with a 12.5 mm probe tube. At 125 and 250 Hz there was 2-3 dB difference between the two me thods in a direction opposite to that expected due to physiological no ise. The reason was probably the actual realization of the sound field . At 4 and 6.3 kHz the objective results were 7 dB lower, probably due to dips at the probe tip in the standing wave in the ear canal. The o bjective method is much faster and gave slightly smaller standard devi ations, which support the idea to use that as a standardised method in the future. However, the optimal microphone technique has still not b een found.