Studies On The Measurement Accuracy Of Random-incident Scattering Coefficient In Scaled-down Reverberation Room And On The Sound Scattering Property Of Popular Schroeder Diffuser

The acoustic property of the hall is not only determined by their geometry,but also by the acoustic characteristics of the surfaces,including their absorption and diffusion characteristics.As an important coefficient to evaluate the ability of surfaces' sound diffusion,scattering coefficient plays an important role in the diffuser design and in the computer simulation model to predict the sound field of the hall.In 2004,the International Standard Organization issued the standard ISO 17497-1 for measuring random incident sound scattering coefficient in reverberation room,which is equally adoptable to the measurement of full-size and scaled-down reverberation rooms.The process of measuring the scattering coefficient in reverberation chamber is complex,and there are many factors influencing the measurement accuracy.Compared with full-size measurement,the interested frequency range of scale-down measurement is in high frequency,which is more easily affected by various factors such as environment,measurement settings,etc.Therefore,in this paper,the factors influencing the measurement accuracy of scattering coefficient in scale-down reverberation room are systematically studied.Flowing are the main work and conclusions obtained in this study:1.Establish a scattering coefficient measurement system in 1:10 scale-down reverberation room and verify its effectiveness,including the measurement of the reverberation radius and the uniformity of the sound field,the verification of the correction of the phase-locked average processing.In addition,the repeatability of the electrical spark pulse sound signal is measured and analyzed in the semi an-echoic chamber.The results show that the electrical spark pulse signal has very good repeatability in the frequency range of 1k Hz to4 k Hz,and shows a high sound pressure level over a wide frequency range,which meets the requirements of the scattering coefficient measurement in ISO 17497-1.2.A series of comparative experiments are carried out in the scaled-down reverberation room to explore the factors that affect the measurement accuracy of scattering coefficient,including the the source position,the receiver position,the recording method of the room pulse response,the phase-locked average method and the manufacturing accuracy of the spacemen.These five aspects differently affect the measurement accuracy of the scattering coefficient.Based on the comprehensive analysis of the influence of various factors,the suggested measurement set-ups of the scattering coefficient in the 1:10 scaled-down reverberation room is proposed: 4 source positions,8 receiver positions,36 impulses for phase-lock averaging and multichannel recording technology.In addition,in order to avoidthe influence of various factors and improve the accuracy of scaled-down measurement,the relevant suggestions are given in this paper,which can provide some help and guidance for scaled-down measurement in the future.3.In the 1:10 scaled-down reverberation room and the full-size reverberation room,the scattering coefficient of three different specimens was measured,and the accuracy of the 1:10scaled-down scattering coefficient measurement and the full-size measurement were analyzed.The research analysis the coincidence of the results measured by two reverberation chambers,the standard deviation analysis of scattering coefficient and reverberation time,and the comparison of 95% confidence range measured in two reverberation chambers.The comparative analysis results show that the 1:10 scaled-down measurement system and the suggested measurement set-ups can obtain the scattering coefficient results with the same accuracy as the full-size measurement,which lays the foundation for promoting the scattering coefficient measurement of the scaled-down reverberation chamber and the establishment of the scattering coefficient database in the future.4.The scattering characteristics of two kinds of Schroeder diffuser,the Maximum Length Sequence(MLS)diffuser and the Quadratic Residue diffuser(QRD)are studied.In a1:10 scaled-down reverberation chamber,the scattering coefficients of 7 MLS diffusers and 3QRDs were measured,and the sound scattering characteristics of the two kinds of diffusers with frequency,structure depth and period length were analyzed.On the one hand,the results of this study could provide some guidance on the diffuser design.On the other hand,it can also provide reliable referencing data for acoustic engineers in indoor acoustic design.