Date of Award

2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Ntuen, Dr. Celestine A.

Abstract

This study was conducted to develop quantitative models for Acceptable Noise Level (ANL) under air conduction (AC) listening conditions. Experimental results on the effects of frequency bandwidths on ANL under two listening conditions involving earphones and loudspeaker (sound field) with high and low frequencies and babble noise and white noise revealed: (a) there are statistically significant interactions among the background noise types, the background noise frequency bandwidths and signal source; (b) background noise and noise frequency bandwidths have effects on listener discriminability bias toward the noise and the signal intensity; (c) different listening conditions had different ANL thresholds; and (d) a significant difference existed between listeners’ Minimum ANL threshold under earphone listening and air conduction listening. The findings revealed that ANLs at different loudspeaker locations were not significantly different statistically from one another. The psychophysical parameters revealed that males had a higher positive discriminability bias toward signal and noise intensities at all locations, except at the 315 degree azimuth; female listeners had higher discriminability biases (β) toward sound at the 315 degree azimuth. For example, the β value for males under signal alone was 0.2095 compared to females’ value of 0.23 at the 315 degree location. Under noise only, male β values were all superior to those of females with values higher than 0.22 against less than 0.1 for females at the 180-, 225-, and 315-degree locations. The result showed that the minimum ANL threshold and the listeners’ discriminability biases toward sound could be found at the 315-degree loudspeaker location. Finally, a study to determine the differences between ANL and Speech Comprehension in Noise Level (SCNL) was not significant. However, the sensitivity toward sound intensity was higher under ANL than SCNL. This is because ANL is the willingness to work in noisy conditions while SCNL seeks meaning out of signals.

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