Urban vegetation—especially vegetated roofs—has real potential for noise mitigation. But accurately measuring their acoustic properties in situ is not as straightforward as it seems.
In our new paper, “Influence of transducer locations on acoustic impedance prediction in porous systems with application to vegetated roofs,” we take a close look at how small errors in source and microphone positioning can strongly affect the prediction of acoustic impedance when using the multiple-geometry technique.
🔍 Key findings:
- Even millimetre-scale errors in transducer locations can lead to large deviations in predicted impedance and material properties
- Harder and layered porous systems (like vegetated roofs) are particularly sensitive
- To obtain accurate and unique impedance predictions, transducer positions should be determined within ±5 mm
- Practical guidance is provided for setting tolerances in experimental setups
These results highlight why careful geometric control is essential when characterising complex porous materials—and why this issue deserves more attention in field measurements of green infrastructure.
Authors: Chang Liu, Fotis Georgiou and Maarten Hornikx
📄 The paper is available here:
👉 https://doi.org/10.1016/j.apacoust.2025.111213
Building Acoustics TU/e 