Study On Key Parameters Of Secondary Sound Source Of Low Frequency Active Noise Control In Semi Free Acoustic Field

With the development of society, more and more low frequency noise have influence on people’s lives, and endanger the people’s health. Some large internal-combustion engine in a certain natural gas station produce large exhaust noise when they are running, which is wideband and mainly low frequency. With the application of a mechanical muffler, the noise reduction of low frequency (mainly infrasound) is still insufficient, and the nearby residents still reflects the natural gas engine noise have a certain influence on their lives. Increasing mechanical muffler size to increase the noise reduction is impossible, so the active muffler must be used, therefore the active noise control in outdoor acoustic field has become a key research.The method, which used in the free acoustic field to deduce volume velocity of the secondary sound source of active noise control, was used in the semi free acoustic field, and deduced the mathematical expressions of the volume velocity of the secondary sound source. Based on the mathematical expressions, we study the effective methods of active noise control with the aim of minimum sound pressure and mimimum sound power. Furthermore, the method of active noise control in outdoor acoustic field was put forward, which maybe effective.Based on the acoustic simulation software "Virtual.Lab Acoustics", we verified the active noise control methods in semi free acoustic, and analyzed the variation law of noise reduction with the distance variation. Further consideration of engineering application, the key parameters of the secondary sound source will appear error, so the variation law of noise reduction with amplitude and phase and frequency change of the secondary sound source was studied.Engine exhaust noise in a certain natural gas station was tested, and a quantitative analysis of relation between low frequency noise reduction and volume of resonant cavity of machinery muffler. Then we simulated the natural gas station acoustic field, in which the active noise control to a point source is simulated, and found the appropriate secondary sound source location and volume velocity which can reduce volume of resonant cavity, while increasing the noise reduction. This paper is based on engineering application, considering the value of the engineering application, proposed the vibrator driving the piston motion insteading of the speaker as the secondary sound source, and analysed the feasibility in the engineering application.This paper combined the theory and simulation results, and the methods of active noise control in semi free field and outdoor acoustic field have a certain reference value in engineering application...