Analysis of the binaural speech transmission index in classrooms
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Bachelor Thesis of Wagener, Julia
The point in time when the human ear starts to perceive sound as noise is subjective. Starting at a young age, even children are exposed to loud noises every day. However, conventional and standardized measurement microphones cannot record how complex sound or noise is perceived by humans. The first binaural models, which have been developecl in psycho- and room acoustics, are only based on the body geometry and the cognitive perception of adults. lt is not known yet whether these models can also be applied to children, since physiology and perception differ from those of adults. Initial research has already been carried out in this field which has not yielded any significant results yet. This bachelor thesis exa.mines the effects of different recorcling methocls on the binaural speech transmission index with an adult ancl a child artificial head, as well as with a reference microphone. An inclirect and a direct rneasurement method accorcling to DIN EN 60268-16 of May 2012 are used to measure the speech transrmission index. The inclirect method is based on a rnathematical rnodification of the impulse response using the Schroeder equation, which is used to calculate the moclulation transfer function. In the direct measurement method, on the other hancl, the speech transmission index is measured using a rnodulated test signal. The influences of the three different receivers in both measurernent methods are compared in this paper and the advautages and disadvantages are show in consideration of the workload and above all based on the results. The research confirrned that binaural recording techniques correspond more to human speech intelligibility than recording with omnidirectional microphones. lt also revealecl that there is no significant difference in the values of the speech transmission index for adult ancl child artificial heacls, neither for the indirect nor for the direct measurement method. Since the evaluation results of the inclirect and direct measurernent methods are comparable, it is recommencled to use the indirect measurement method for room acoustic measurements of the speech transmission index, considering the required time.