The modelling of vibro-acoustic properties of plates usually requires the hypothesis of diffuse conditionsof the vibrational field. For heavy-weight homogeneous isotropic plates, this condition is met startingfrom low frequencies. Nevertheless, the same hypotheses do not hold when applied to stiff, inhomoge-neous and non-isotropic materials, like wood, thus its modal behavior needs to be addressed with moredetail. The aim of the work is to benchmark theoretical methods and experimental measurements thatallow to estimate when the transition from modal to diffuse field occurs in Cross Laminated Timber(CLT) elements. For this purpose, the diffuseness of the vibrational field has been investigated throughthe experimental evaluation of the mode count and the modal overlap factor on a pilot CLT panel.Measurements of the spatial distribution of modes, impulse responses, dispersion relations and drivingpoint admittance were conducted in laboratory on an 8 m2CLT plate. The analysis of the results allowed,on the one hand, to directly estimate the two parameters, and on the other, to provide input data neces-sary to evaluate and compare different theoretical models. Results of direct measurements, performed upto 550 Hz, show that the number of modes occurring in one-third octave bands exceeds the standardthreshold of 5 only at 500 Hz, whereas the modal overlap factor is lower than the standard thresholdof 1 for most of the modes. This indicates that the vibrational field is mainly non-diffuse in the mid-low frequency range, due to the small number of modes combined with a low damping of the CLT plate.Nonetheless, measurements of modal reverberation time and structural reverberation time in one-thirdoctave band provided consistent results, implying that modal decays are the major contributors to theone-third octave band decay. Furthermore, comparisons with theoretical models show that the drivingpoint admittance proved to be the best method of analysis, requiring simple measurement setup and sig-nal processing, whereas the ISO 10848-4 is affected by the thin plate hypothesis and underestimates themode count at mid-high frequencies.
Morandi, F., Prato, A., Barbaresi, L., Schiavi, A. (2020). On the diffuseness of the vibrational field of a cross-laminated timber plate: Comparison between theoretical and experimental methods. APPLIED ACOUSTICS, 159, 107104-107113 [10.1016/j.apacoust.2019.107104].
On the diffuseness of the vibrational field of a cross-laminated timber plate: Comparison between theoretical and experimental methods
Morandi, F.
;Barbaresi, L.;
2020
Abstract
The modelling of vibro-acoustic properties of plates usually requires the hypothesis of diffuse conditionsof the vibrational field. For heavy-weight homogeneous isotropic plates, this condition is met startingfrom low frequencies. Nevertheless, the same hypotheses do not hold when applied to stiff, inhomoge-neous and non-isotropic materials, like wood, thus its modal behavior needs to be addressed with moredetail. The aim of the work is to benchmark theoretical methods and experimental measurements thatallow to estimate when the transition from modal to diffuse field occurs in Cross Laminated Timber(CLT) elements. For this purpose, the diffuseness of the vibrational field has been investigated throughthe experimental evaluation of the mode count and the modal overlap factor on a pilot CLT panel.Measurements of the spatial distribution of modes, impulse responses, dispersion relations and drivingpoint admittance were conducted in laboratory on an 8 m2CLT plate. The analysis of the results allowed,on the one hand, to directly estimate the two parameters, and on the other, to provide input data neces-sary to evaluate and compare different theoretical models. Results of direct measurements, performed upto 550 Hz, show that the number of modes occurring in one-third octave bands exceeds the standardthreshold of 5 only at 500 Hz, whereas the modal overlap factor is lower than the standard thresholdof 1 for most of the modes. This indicates that the vibrational field is mainly non-diffuse in the mid-low frequency range, due to the small number of modes combined with a low damping of the CLT plate.Nonetheless, measurements of modal reverberation time and structural reverberation time in one-thirdoctave band provided consistent results, implying that modal decays are the major contributors to theone-third octave band decay. Furthermore, comparisons with theoretical models show that the drivingpoint admittance proved to be the best method of analysis, requiring simple measurement setup and sig-nal processing, whereas the ISO 10848-4 is affected by the thin plate hypothesis and underestimates themode count at mid-high frequencies.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
