Active And Passive Composite Control Of Ventilation Duct Noise

Ventilation ducts are all over the corner of large buildings.When they work,they are usually accompanied by the noise of mechanical fans and airflow.The broadband noise intensity is too large,especially the low-frequency noise will affect people's physical and mental health.Aiming at the noise in the ducts,the commonly used noise reduction method is passive noise control(PNC),that is,the sound absorption structure and materials are used to improve the pipeline structure,so that the noise can be partially attenuated.However,passive noise reduction has some disadvantages,such as low-frequency noise effect is limited,equipment volume is too large and cost is too high.Fortunately,active noise control(ANC)can make up for these shortcomings,and can eliminate low-frequency noise with small and micro devices.In order to achieve a satisfactory noise reduction effect,this project uses the combination of active noise reduction and passive noise reduction,in order to reduce the noise of the whole frequency band.The main research work of this paper is as follows:According to the pipe sound field theory,a passive noise reduction muffler structure is designed.The actual test results show that the muffler can effectively attenuate the middle and high frequency part of the noise,and the passive muffler can reduce the sound feedback phenomenon to a certain extent.The explanation is given from the perspective of the transfer function of the control system.In order to reduce the influence of the air flow in the ventilation duct on the signal acquisition of the reference and error microphone,a modular inner core structure is designed,and the microphone is placed in the sound absorption inner core.The actual test shows that the accurate and effective noise signal can be obtained.The criteria of reference and error microphone placement in practical engineering application are given.For the acoustic feedback problem of feedforward control system,in addition to the passive muffler mentioned above,the influence of acoustic feedback is further suppressed in the algorithm,and the leaky Fx LMS algorithm with feedback neutralization,which is more stable in practical engineering,is selected.Finally,the performance of the active passive combined system is verified by experiments.The results show that the passive part of the system attenuates the noise from 500 Hz to a certain extent.In the windless static experimental environment,the active noise control system can achieve a maximum noise reduction of about 20 d B in the frequency band of 100-250 Hz,and the effect gradually decreases with the increase of frequency.In the wind dynamic experimental environment,the active noise control system can still operate normally,and the noise reduction effect is about 10 d B in the frequency band of 100-250 Hz.