In this paper an improved method for the prediction of the sound transmission loss of multilayered finite structures, like glazing will be presented. The sound transmission loss of an infinite structure is predicted with a common transfer matrix as a function of the angle of the incident sound wave. Then Villiot's spatial windowing method is applied to take into account the finiteness of the element. Usually an ideal diffuse distribution of the incident sound power is assumed and the prediction results are integrated over all angles of incidence. The obtained prediction results tend to underestimate sound transmission loss due to the dominance of the small values for gracing incidence. Often simple ad-hoc corrections are used for improvement, like Beranek's field incidence, that fail for multilayered structures. Kang suggests that the incident sound power on a surface of a room generally is Gaussian distributed on the angle of incidence and introduces a weighting function for the integration of the prediction results over the angles of incidence. New in this paper is that spatial windowing as well as a Gaussian distributed sound power is considered for the prediction of the transmission loss. The results of the prediction are validated by experiment.
Most statistical and ray-tracing computer models take into account the absorption of sound by air when calculating the reverberation time. Extensive research by many scientist lead to the standardized calculation model for pure tone air absorption. The phenomenon was discovered from a room acoustical point of view by Sabine, while the further development of the calculation model took place in the fields of physics and environmental noise. As a result, several parameters and units are used for the same phenomenon. However, air absorption is calculated for pure tones, while room acoustics calculations are performed for frequency bands. Most computer models use the center frequency of the normalized frequency bands to calculate the air absorption by the pure tone method. Frequency band reverberation measurements under laboratory and practical conditions show that errors larger than the JND are made in calculating the air absorption by this 'center frequency method'. No literature is found that provides an accurate air absorption calculation for frequency bands.
To compare the acoustic performance of a building element with given sound insulation requirements, measurements need to be done. Generally, a broadband noise source is used according to international standards. This method does not always work in practice due to high sound insulation values or high background noise levels. It is very inconvenient from a practical point of view or even impossible to perform an accurate sound insulation measurement for all frequency bands. A solution to this problem can be found in deconvolution techniques using MLS or sweep signals. It is possible to increase the signal to noise ratio with these techniques by averaging measurements and spreading out the spectral sound energy in time. As a result an efficient use of available sound power is possible. In a laboratory the use of MLS or sweep signals as a source signal and deconvolution as a measurement technique to obtain the sound insulation under noisy conditions was investigated.
In residential buildings many people are annoyed by noise caused by their neighbors, including structure-borne sound caused by drinking water, sanitary, and other installations. In different building regulations, limits are set to the maximum allowable sound level caused by installations in a room. However, predictions of the sound level in the design stage are not possible. In this research, a framework for structure-borne sound transmission models for pipe systems, including source characterization, has been developed. Further, the application possibilities of existing calculation methods in the quantification of the sound transmission have been investigated. For example, the application possibilities of the finite-element method (FEM) and statistical energy analysis (SEA) depend on the element type, including dimensions and material (pipe, mounting, or building structure), the wave type, and the frequency area. By combining both methods, calculations for the whole audible frequency area seem possible. Some models are presented, together with calculated values of characteristic parameters. Measurements can be used to complete and validate the models, for example by using a measurement setup based on the plate method. The interaction between calculations and measurements will form the basis for future research. The future research setup is also presented.
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