The Research On A New Method Of Octave Analysis And Its Application In Sound Power Detection

Sound power level is commonly used to evaluate the radiated noise energy of mechanical equipment.It has become an important indicator to measure the quality of mechanical equipment.Accurately measuring sound power,not only can help people objectively evaluate the noise performance of mechanical equipmen t,but also study the causes and characteristics of noise and find effective ways to reduce noise.The octave analysis is an important part of the sound power detection.For the deficiencies of the existing octave analysis methods such as large amount of computation,poor real-time performance and large errors in the low-frequency range,an octave analysis method based on a subsection sampling FFT algorithm is proposed in this thesis.The analysis method was applied to the sound power measurement system.Combined with the development trend of the current instrument virtualization,the sound power measurement and analysis system was designed and developed based on the hardware platform of “Microphone + Signal Conditioning Circuit + Data Acquisition Card” and the virtual instrument technology,computer technology,and the Acesss database technology.Firstly,the research background and significance of sound power detection are introduced,which provides a theoretical basis for the necessity of constructing a multi-channel sound power measurement system and improving the octave analysis method.The research status and development trend of acoustic power measurement and octave analysis methods are described,which lays a theoretical foundation for the design method of sound power measurement and analysis system.Secondly,the existing sound power measurement methods are introduced.The applicable measurement conditions,advantages and disadvantages of each method are compared and analyzed.The basic principles of the reflective surface engineering method used in this thesis are highlighted and the measurement steps are summarized.Thirdly,the method of the octave analysis is studied and the shortcomings of the existing methods are analyzed.A subsection sampling FFT algorithm is proposed.Multi-resolution FFT analysis is achieved by sampling to reduce the low-frequency error.So that the number of sampling and FFT processing can be reduced and the analysis speed can get improved.The FFT method is used to achieve A frequency weighting,and further reduce the complexity of the sound power measurement algorithm.Then,a digital design and implementation method of the algorithm is given.The performance of sound pressure level spectrum analysis and the relative attenuation value of frequency band are tested.At the same time,it is compared with the fixed-sampling FFT algorithm and the multi-sampling rate FFT algorithm to prove the superiority of the proposed algorithm.Finally,by analyzing the system requirements,the overall design of the system is given.The hardware part gives the design plan of the signal conditioning unit;the software part describes in detail the design and implementation of each functional module,including three modules: data acquisition,data measurement and analysis and data management;and the reliability and optimal design of the system.The simulation and measured results show that the measurement accuracy of the proposed octave analysis method and A-frequency weighting fully meet the requirements of sound level meter(Class 1)in the national standard of GB/T 3241-2010.The method compared with the octave analysis method based on multi-sampling FFT can reduce the amount of computation up to 88.9% and can effectively improve the analysis speed.The sound power measurement and analysis system designed in this thesis meet the requirements of ISO 3744-2010 for the reflective surface engineering method.It can realize the parallel processing of nine signals,and with the advantages of such as high measurement efficiency and intelligence,simple operation,human-computer interaction friendly,stable and reliable performance of system and so on.