Coherent Prediction Method And Parametrization Study Of Sound Field In Open-plan Offices

Open-plan office is a typical flat space,whose length and width are much larger than the height.Noise interference,mainly voice noise,has become an important factor affecting the work efficiency of officers inside.Therefore,the ceiling or other surfaces are usually set as absorptive with sound-absorbing material.Such an internal space environment can be abstracted acoustically into a flat space with a large area of sound absorption boundary.For the sound propagation,the traditional statistical acoustic method and the incoherent geometric acoustic method can only be used for rough estimation,while the wave theory method can only deal with the regular shape space.The coherent image source method based on geometric acoustics can simplify the calculation while take the fluctuation of sound field into consideration,that is more suitable for solving the sound field in a flat space with a large sound absorption surface both accurately and quickly.In this paper,the coherent image source method and parameterization study of sound field in open-plan office are developed in the following three aspects:Firstly,based on the principle of image source method,the influence of ceiling sound absorption parameters on the attenuation characteristics of sound field in a flat space with two infinite parallel boundaries and a point source is investigated theoretically,and the attenuation characteristics of flat space sound field is compared with free sound field of point source,semi-free sound field of point source and free sound field of line source.The results show that when the ceiling is a high reflective surface,the attenuation of sound field of point source in a flat space with lower frequency is similar to that of cylindrical wave,and with the increase of sound absorption capacity of the ceiling,the attenuation characteristics of sound field gradually approach the attenuation of semi-free sound field of point source.Then,the coherent image source method proposed by Min et al.is extended to predict the sound field in a rectangular hexahedron flat closed space with a high sound absorptive ceiling,and the extended model is validated numerically based on the wave theory.In the numerical example,a 16 m × 25 m × 3 m flat enclosure is established,and the changes of Sound Pressure Level in X direction,Y direction and Z direction at 500 Hz and 1000 Hz under different boundary admittances are calculated respectively.At the same time,the spectrum of sound pressure levels at different receiving points in space at 100 Hz to 1000 Hz is calculated and examined.The numerical results show that the extended coherent image source method has a high predictive consistency with the wave theory.Then,based on the 1:10 scale model of flat enclosure,the prediction accuracy of the extended model of coherent image source method is studied experimentally.In the experiment,a 1:10 scale model with a size of 0.9m × 1.3m × 0.24 m was established;a small dodecahedron point sound source with a diameter of 3.5cm was designed,and its frequency response curve and directivity were measured and analyzed;different sound absorption characteristics of boundaries in scale model were designed,and a variety of sound absorption materials were selected based on the measurement of incidence sound absorptive coefficient.The experimental results and error analysis show that,compared with the existing geometric acoustic prediction methods,the extended coherent image source model in this paper has a higher coincidence with the measured results.