Research on Performance Measurement of Acoustic Material Based on Wide-band Pulse Method

Author:Dai Yang

Supervisor:yang jian hua


Degree Year:2017





Acoustic material is widely used in sound insulation,damping,sound absorption,underwater equipment and engineering,and it’s of great importance to study the parameter measurement of acoustic material.At present,field measurement of air acoustic parameters and accurate measurement in low frequency of acoustic parameters are technical challenges in this area.For the air acoustic material measurement method,both the impedance measurement method and the reverberation chamber method are off-line measurement of the laboratory method.In practical operation,it should be provided an ideal sound field environment,such as standing wave field,traveling wave field and reverberation field.Although these two methods have been widely used,and corresponding measurement standards are established,results of the laboratory methods and these of actual application have a certain gap.The existing free-field method can be conducted in the field,but the research on the wide-band pulse method measurement is not extensive.Therefore,the research of field measurement is of great significance to develop the on-line measurement system of acoustic parameters.The measurement of performance of underwater acoustic material is mainly implemented in the laboratory platform such as water tube,anechoic tank and pressure tank.The diameters of domestic water tubes are 57 mm,120mm and 208 mm,and height is between 3m and 10 m.Due to the limitation of the emitting signal and the measurement procedure,the measurement accuracy of the sound absorption and sound insulation in low frequency band(less than500Hz)still can’t meet the practical requirement.Therefore,it is very important to study acoustic material measurement at low frequency in water tube.Aiming at the problem of portable field measurement of air acoustic material and the low frequency measurement of underwater acoustic material,the main innovative achievements are as follows:In order to solve the problem of noise sensitive and regularization parameter selection in the frequency domain,a For-Wa RD is adopted.After the shrinkage in Fourier domain,the function is shrunk in Wavelet domain to enhance the edge information of the signal and improve the SNR of the estimated signal.Inspired by For-Wa RD,a For-EMDRD is proposed,which proceeds with shrinkage of ideal deconvolution in EMD domain to enhance the edge information and SNR of the estimated signal.Simulation experiments were carried out by means of pure inverse filter,Wiener inverse filter,For-Wa RD,and For-EMDRD.The For-EMDRD was carried out in the air acoustic impedance tube.Aiming at the problem of wide-band pulse generation of sound absorption measurement in field,the inverse filter method in time domain was used.LS inverse filter and MMSE inverse filter were used respectively to realize the generation of the broadband Butterworth pulse wave on the free field test platform based on GPIB bus.The time domain and frequency domain characteristics of the waveform satisfy measurement requirements.The time-domain inverse filter algorithm was further transplanted into the embedded platform.The controllable pulse sound source system based on sb_RIO was constructed on NI single board embedded device sb_RIO 9642 platform,which realized the wide-band pulse generation of the embedded platform.It lays the foundation for the field acoustic parameter measurementFor the CW pulse method in the water tube,it is difficult to separate the incident wave and reflective wave with the decrease of the frequency.After deeply analyzing the sound field and acoustic wave propagation in underwater acoustic tube,the wide-band pulse method was applied.The pulse wave of short duration in time,rich component in frequency was used instead of the conventional CW pulse wave.The three-step method was used to generate the broadband zero-phase signal in water tube.The performance of the acoustic material was measured.The results of this method have good agreement with the standard CW pulse method in 3k ~ 8k Hz,showing that the wide-band pulse method is feasible and accurate.At the same time,according to the intrinsic relationship between acoustics and mechanical properties of the material,the method of calculating the dynamic mechanical parameters was deduced,and the Young’s modulus and the loss factor were calculated by reflection coefficient method.Then,a number of repeated experiments were conducted to calculate the uncertainty.In the water tube of the monostatic transducer,the response of the transducer may lead to the case that the length of the excitation signal is too long to generate of the wide-band pulse.Therefore,the thesis applied a "post-processing" inverse filter method.The simulation work was conducted to show the advantage over "pre-processing" inverse filter.On this basis,the "post-processing" inverse filter method was applied to the measurement of the water-filled tube.The results show that,under the same hardware test platform,"post-processing" inverse filter method can extend the low frequency compared with CW pulse method and "pre-processing" inverse filter method,and the low-frequency is able to reach 350 Hz.In the water tube of the transmitter-receiver configuration,it is difficult to achieve good results at low frequency below 300 Hz.The transmitter-receiver configuration was proposed,and hydrophone was used as the receiver.At first,broadband pulse sound generation contrast experiments were conducted,with the transducer and hydrophone as a receiver device respectively.The sound generation results were compared to indicate that the hydrophone has advantages over transducer in terms of acting as a receiver.Then,the samples were measured by the single microphone broadband pulse method,the transfer function method and the ouble microphone broadband pulse method,respectively,and the results were in good agreement with those above 200 Hz.The feasibility of using the broadband pulse method was proved which lays the foundation for the construction of miniature water tube.