Study And Application Of Sound Intensity Measurement For Impulse Response Signal

Sound intensity technology has been widely used in noise measurement for its advantages including the convenient test procedure and low requirements for test environment.Reasonable sound intensity analysis can provide a reliable basis for further noise control.In recent years the requirement for noise control has been more and more strict.In order to further reduce the noise,sound intensity measurement tends to be specialized and precise aiming at different forms of noise.As the technology of signal extraction is becoming more and more mature,it is possible to calculate the sound intensity of different forms of noise in a targeted way.The impulse response signal exists in engineering noise widely which can transmit a large amount of sound energy in a short time.Take engine noise as example,the impulse response signal forms when the piston impacting cylinder wall or the valve impacting valve seat.In this paper,sound intensity analysis is applied to the impulse response signal.Firstly,the classic cross spectrum method is applied to analyze the sound intensity of impulse response signal.It is found that the sound energy scatter at different frequency points on the spectrum.So the actual sound intensity of the signal can not be known from the spectrum intuitively.When cross spectrum method is used to analyze the sound intensity of signals containing multiple impulse response components,even negative sound intensity appears on the spectrum.As the cross spectrum method can not analyze the sound intensity of impulse response signal clearly,a method for calculating the sound intensity of impulse response signal is proposed in this paper: extract impulse response component from the original signal with the signal analysis method,then calculate the actual intensity of the impulse response component with the time domain sound intensity formula.The inner product method is used to extract the impulse response signal: with the inner product method,the characteristic parameters of impulse response signal are identified,and the impulse response signal is reconstructed according to these characteristic parameters.The actual sound intensity value of the signal can be calculated finally.The simulation results show that: when the attenuation coefficient is small,the inner product method can extract the impulse response signal accurately and the sound intensity can be calculated effectively;however when the attenuation coefficient is large,the accuracy of signal extraction decreases,and the result of sound intensity calculation is not accurate.Accurate extraction of impulse response signal is the key to effective solution of signal intensity.In order to improve the precision of impulse response signal extraction,the orthogonal system is constructed to identify the characteristic parameters of the impulse response signal.Then search the maximum value of projection of the response signal on the orthogonal system to get the characteristic parameters.Reconstruct the impulse response signal with these characteristic parameters,and the intensity of impulse response signal can be calculated finally.The simulation results show that: this method can effectively extract impulse response signals under different attenuation coefficients and calculate their sound intensity values accurately.The sound intensity of the combined impulse response signal is further analyzed with iterative method.The simulation shows that the multiple impulse response components in the signal can be extracted effectively with the iterative method,and then the sound intensity of each impulse response component can be obtained accurately.The method is applied to the sound intensity calculation of impulse response signal of a certain type of engine.The calculation results show that this method can extract multiple impulse response components in noise and calculate the sound intensity value accurately.Compared with cross spectrum method,it is found that the main peak values of the signal in the spectrum obtained by the cross spectrum method are distributed around 1000-1300 Hz,and the secondary peak values are scattered around 450-550 Hz.We can not clearly identify the actual source and intensity of the noise with the sound intensity spectrum.With the method in this article,the main sound energy of the engine can be locked mainly from the impulse response signals on 1170 Hz and 507 Hz,and the result showed that the energy of impulse response component accounts for 46% of the total sound energy.It is found that this method can analyze the acoustic intensity of impulse response signal clearly,and reflect the actual characteristics of this kind of signal effectively.The calculation results provide a clearer basis for further noise reduction.