Research On Sound Quality Prediction Of Motorcycle Muffler Based On SVR

With the improvement of living standards,people are paying more and more attention to motorcycle noise,vibration and harshness(NVH).The exhaust noise is one of the main noise sources of motorcycle.Its sound pressure level should be strictly controlled and its sound quality should be improved.In this paper,the sound quality of muffler of 150ml riding motorcycle is taken as the research object,and a support vector regression machine(SVR)sound quality prediction model based on genetic algorithm is established by using a method of combining subjective and objective evaluation,and the noise attenuation analysis and sound quality prediction of the improved muffler after the analogy are carried out.The main research work is as follows:First,subjective and objective evaluation tests is conducted on the exhaust noise of thirteen 150ml riding motorcycles.Thirteen 150ml riding motorcycles are selected,then a steady state test is performed on them in a semi-anechoic room under the condition of stationary load,no-load and 1600r/min,2000r/min,3000r/min,4000r/min and 5000r/min and 65 effective exhaust sound samples are obtained.The objective quantities of 65 effective exhaust sound samples,such as loudness,sharpness,roughness,fluctuation strength,kurtosis and A-weighted sound pressure level,are calculated in LMS Test.lab and the subjective evaluation test of 65 effective exhaust sound samples is performed using paired comparison method with preference as an index.The correlation between subjective and objective variables is analyzed by SPSS.The result shows that only sharpness,roughness and kurtosis are related to the preference.Second,a SVR sound quality prediction model based on genetic algorithm is established.The precision of the prediction model is influenced by the parameters of SVR.In this paper,a genetic algorithm is introduced to optimize the parameters.The subjective and objective results are trained and tested in the libsvm toolbox loaded in MATLAB,taking sharpness,roughness and kurtosis as inputs and preference as output.The correlation coefficient R~2=0.9563 of the training results shows that the prediction accuracy is high;the correlation coefficient R~2=0.9434 of the test results shows that the prediction model has better generalization ability.Then,a motorcycle muffler is analyzed and improved.The 1/3 octave method is used to analyze the test data of the motorcycle to be improved and the standard motorcycle.The improvement direction of the muffler is determined to increase the sound attenuation of frequency of 1250Hz and above,and the improvement is applied according to the structure of the standard motorcycle.Finite element method is used to analyze the improved muffler.The result shows that the noise attenuation in the two frequency bands of 2190Hz to 2310Hz and 2400Hz to 2470Hz is reduced,and other frequency bands basically reach the improvement target.It shows that the improved muffler has better noise elimination effect.Finally,the SVR prediction model based on genetic algorithm is applied to predict the sound quality of the improved muffler.In order to verify whether the sound quality of the improved muffler is improved,the model is used to predict the sound quality.The result shows that the sound quality is improved at all five rotation speeds,and the preference value is increased to the maximum at 5000 r/min,which increases by 14.18,while the preference value increased by the minimum at 1600 r/min,and increased by 8.08,indicating that the improved structure improves the exhaust sound quality.At the same time,a subjective evaluation test is conducted on the improved structure,and the correlation coefficient between the predicted value and the test value shows the correlation coefficient R~2=0.969,and the prediction error is less than 3%at the five speeds,indicating that the sound quality of the improved muffler is improved.The research in this paper shows that the SVR sound quality prediction method based on genetic algorithm can better predict the exhaust sound quality of 150ml riding motorcycle,which shows that the prediction method has the value of engineering application.