Application Of The 3-D Sound Intensity Method In Measurements Of Sound Insulation Of Building Elements

Sound insulation of building elements is an important means to improve the indoor acoustic environment.Although the sound transmission loss could be obtained by the conventional airborne sound insulation measurement,there is no way to predict the location of the sound source and the measuring accuracy is sensitive to different conditions.In this paper,a new 3-D sound intensity measurement system is used to calculate the sound intensity vectors and estimate sound insulation property of the building elements.Compared with the conventional approaches,3-D sound intensity method has some advantages such as sound localization,degree of accuracy and sensitivity.(1)Theoretic study of 3-D sound intensity method.Analogy is the core research method of the theoretic study in this paper due to that the 3-D sound intensity method is the expansion of conventional two-microphone method in three dimensional space.The pressure and particle velocity located on the geometric center of the probe have been estimated by analyzing the spatial geometry relationship of three typical probes.The spectrum of sound intensity vectors with X?Y and Z components which could be used to calculate airborne sound insulation has been obtained.(2)Numerical simulation based on Matlab.In order to validate the performance of the 3-D intensity probes further,numerical analysis models have been established to analyze the changing of the magnitude bias and directional bias related to frequency under harmonic plane waves and spherical waves.The results of the numerical simulation indicate that both magnitude bias and directional bias increase exponentially in main audible frequency range.The magnitude bias which meet accuracy requirements are less than 2dB within the range between 0Hz and 2kHz supposing the circumradius of 3-D sound intensity probes R=0.025 m and the sample size n=5000.In terms of directional bias,it is close to 0.5° when f=1kHz for the tetrahedral microphones probe,which meet the accuracy requirements.(3)Measurement system design based on LabVIEW.The new 3-D sound intensity measurement system in this paper is based on NI-PXI.Graphical programming language has been introduced for calculating 3-D sound intensity vectors and evaluating the performance of building elements.The new 3-D sound intensity measurement system consists of data acquisition module,pressure module and 3-D sound intensity module.DAQ Assistant has been used to acquire a semaphore and parameters such as sampling rate,circumradius and sensitivity have been defined which are essential for storing and reading signals in data acquisition module.Time domain and frequency domain analysis could be accomplished in pressure module.The average mode of FFT operation could be defined and the signals could be weighted in pressure module too.In terms of 3-D sound intensity module,the sub-VI for cross-spectral analysis could be invoked to calculate 3-D sound intensity vectors which could be used to calculate sound transmission loss,then the information of the amplitude and angle are output to the waveform display.(4)Experimental verification in lab.In order to validate the feasibility of the system further,the data measured by 3-D sound intensity measurement system is compared to the one measured using the pressure method and 1-D sound intensity method in building sound acoustic insulation lab.The experimental results demonstrate that the 3-D sound intensity measurement system can be used to calculate the sound transmission loss as well as describing the acoustic defect of the building elements,and it is suitable for the field measurement.