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On the diffuseness of the vibrational field of a cross-laminated timber plate: Comparison between theoretical and experimental methods

机译：关于交叉层压木板振动场的扩散：理论与实验方法与实验方法的比较

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The modelling of vibro-acoustic properties of plates usually requires the hypothesis of diffuse conditions of the vibrational field. For heavy-weight homogeneous isotropic plates, this condition is met starting from low frequencies. Nevertheless, the same hypotheses do not hold when applied to stiff, inhomogeneous and non-isotropic materials, like wood, thus its modal behavior needs to be addressed with more detail. The aim of the work is to benchmark theoretical methods and experimental measurements that allow 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 through the 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 driving point admittance were conducted in laboratory on an 8 m(2) CLT 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 necessary to evaluate and compare different theoretical models. Results of direct measurements, performed up to 550 Hz, show that the number of modes occurring in one-third octave bands exceeds the standard threshold of 5 only at 500 Hz, whereas the modal overlap factor is lower than the standard threshold of 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-third octave band provided consistent results, implying that modal decays are the major contributors to the one-third octave band decay. Furthermore, comparisons with theoretical models show that the driving point admittance proved to be the best method of analysis, requiring simple measurement setup and signal processing, whereas the ISO 10848-4 is affected by the thin plate hypothesis and underestimates the mode count at mid-high frequencies. (C) 2019 Elsevier Ltd. All rights reserved.
机译：平板的振动声学性质的建模通常需要振动场的漫射条件的假设。对于重型均匀各向同性板，从低频开始满足该条件。然而，当施用刚性，不均匀和非各向同性的材料（如木材）时，相同的假设不会保持，因此需要更详细地解决其模态行为。该工作的目的是基准测试的理论方法和实验测量，允许在交叉层压木材（CLT）元件中发生从模态到漫射场的转变时估计。为此目的，通过在飞行员CLT面板上的模式计数和模态重叠因子的实验评估来研究振动场的漫射。在8米（2）CLT板上，在实验室进行了模式的空间分布，脉冲响应，分散关系和驱动点导入的测量。允许的结果分析，一方面，直接估计两个参数，另一方面，以提供评估和比较不同理论模型所需的输入数据。直接测量的结果最多可达550 Hz，表明三分之一八十频带中发生的模式数量仅超过500Hz的标准阈值，而模态重叠因子大多数为1的标准阈值模式。这表明振动场主要是在中低频范围内非漫射，这是由于少量的模式与CLT板的低阻尼相结合。尽管如此，在三分之一八十频段中的模态混响时间和结构混响时间的测量提供了一致的结果，这意味着模态衰减是三分之一八十八个带衰减的主要贡献者。此外，与理论模型的比较表明，驱动点导入被证明是最佳的分析方法，需要简单的测量设置和信号处理，而ISO 10848-4受薄板假设的影响，并低估了在中间的模式计数高频。 （c）2019 Elsevier Ltd.保留所有权利。

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