Speaker
Description
In acoustics, the Bies-Hansen model is a well-established empirical correlation for estimating the airflow resistivity (AFR), supporting the design and evaluation of fibrous acoustic materials such as mineral wool. It provides a mathematical relationship between the physical properties of material—including density and fibre diameter—to AFR. The model’s empirical constants were originally derived for fiberglass materials with negligible binder content, under the assumption of uniform fiber diameters below 15 µm. In the original correlation, fibre diameter was obtained by optical microscopy and represented by a mean value used to fit the constants. In practice, multiple techniques are available for fibre diameter determination, each based on different measurement principles and data interpretation. Moreover, it is questionable if the mean value fully captures the complexity of non-uniform fiber diameter distribution typical for fibrous materials.This study compares several fiber diameter measurement approaches and assesses the agreement between measured AFR and Bies–Hansen predictions when each method’s diameter is used in the model. It outlines how measurement technique selection affects the derived fiber diameter and therefore the predicted AFR.The study highlights that variations in fiber diameter determination methods affect AFR predictions and underscores the need to recalculate the original empirical constants for better alignment with measured values. Recalibration improves model fidelity across materials with different properties and non-uniform diameters, enabling more reliable AFR prediction beyond the original scope of the Bies–Hansen correlation.