Empirical models for artificial and natural rainfall to assess rain noise inside buildings and cars

Rain falling on the roof elements of buildings, or the roof or windscreen of cars produces noise which can interfere with speech intelligibility, acoustic comfort and listening conditions. Laboratory measurements with artificial rain can be used to compare individual elements but there is no established link to natural rain which needs to be assessed in practice. This requires validated prediction models for the structure-borne sound power input from artificial and natural rainfall. For this reason, empirical models have been developed to determine the time-dependent force on horizontal and inclined plates with artificial and natural rainfall. The empirical models were developed using experimental work with wavelet deconvolution for single drops impacting at terminal velocity on a horizontal glass plate with and without a water layer, and an inclined glass plate at angles up to 60. Use of the models to compare different types of rainfall was validated with artificial rain. The validated model has been used to calculate conversion factors between laboratory measurements with artificial rain to other situations with natural or artificial rainfall, and between measurements on elements that are inclined at different angles.