Using near-field acoustic measurements to characterise mechanical and acoustic properties of lightweight building structures

The evaluation of the vibrational field on a certain surface has a great importance in noise control engineering applications. It can be helpful, both for noise reduction purposes, and diagnostic purposes, in product optimisation, or in order to characterise the mechanical properties of the vibrating structure. Accelerometers are still the most used sensors to measure vibration. However, contactless transducers, such as scanning laser doppler vibrometers (LDV), have been widely used recently, presenting several advantages. Near-field acoustic holography may represent a valid alternative to LDV, in order to reconstruct the vibrational field on a surface from sound pressure measurements performed with an array of microphones. This paper presents the preliminary results, of a ongoing project regarding the use of near-field acoustic holography to characterise the elastic and acoustic properties of a lightweight building structure. The used test rig allows to scan the sound pressure over the vibrating surface on a grid of points, using an array of microphones. The panel's dynamic response was used to evaluate its elastic properties. The reliability of this experimental approach was assessed by comparing the results with the ones obtained using miniature accelerometers. These elastic properties were finally used as input data to model sound transmission through the plywood panel using the transfer matrix method, investigating the accuracy by comparing the numerical results with the experimental sound insulation.