Measurements in room acoustics : Uncertainties and influence of the measurement position

Witew, Ingo B.; Vorländer, Michael (Thesis advisor); Ponci, Ferdinanda (Thesis advisor)

Berlin : Logos Verlag Berlin GmbH (2022)
Book, Dissertation / PhD Thesis

In: Aachener Beiträge zur Akustik 37
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2022

Abstract

Regardless of the field, measurements are essential for validating theories and making well-founded decisions. A criterion for the validity and comparability of measured values is their uncertainty. The "Guide to the Expression of Uncertainty in Measurement" (GUM) provides a standardized framework for determining and interpreting measurement uncertainty. Still, in room acoustical measurements, the application of these rules is not yet widespread. Firstly, this is due to the fact that well established 2-CH-FFT correlation techniques rely on a complexprinciple, which is not covered by the classical guide. In addition, the effect of input variables on an individual measurement can only be determined after considerable effort. An example are fluctuations of room acoustical quantities over small distances between measurement locations in concert halls. This variation of the sound field by position is sometimes considerable and can only be predicted in relatively simple boundary value problems. This raises the question of the validity and interpretability of room acoustical measurements.The goal of this thesis is to provide a GUM-compliant discussion of uncertainties in measuring room acoustical single-number quantities. This starts with a structured search of variables that potentially influence the measurement of room impulse responses. In a second step, this uncertainty is propagated through the algorithm that determines room acoustical single-number quantities.Further emphasis is placed on the investigation of spatial fluctuations of the sound field in auditoria. The influence of an uncertain measurement position on the overall measurement uncertainty is discussed. To reach general conclusions, the relation between changes in the measurement location and the corresponding changes in measured room acoustical quantities is investigated empirically in extensive measurement series. To this end, a measurement apparatus was designed that allows automatic, high-resolution sampling of sound fields over large areas. The collected data creates the foundation to apply the principle of uncertainty propagation using a Monte Carlo method.This study shows how precisely a measurement position must be defined to ensure a given uncertainty of room acoustical single-number quantities. The presented methods form a foundation that can be flexibly extended in future investigations to include additional influences on the measurement uncertainty.