An investigation on physical mechanism for active sound absorption structure of flat panel

Active sound absorption structure proposed in recent years has been viewed as an feasible approach to effectively absorb low-frequency reflected sound. Analyzing the physical mechanism of noise reduction can offer theoretical help for some key issues, such as design optimization, the arrangements of secondary sources and error sensors, and selection of the control objectives. Under the minimization of the reflected sound power output, the physical mechanism of noise reduction is investigated by analyzing the changes of reflected sound power and net sound intensity of primary and secondary structures and the distribution of near field sound intensity before and after control. The results show that there are three mechanisms in noise reduction by active sound absorption structure, which are energy restraint, energy absorption and energy offset. In terms of near field sound intensity distribution, the effect of active sound absorption can be revealed by amplitude restraint and direction adjusting of the sound intensity. The normal sound intensity of the reflected sound wave is negative before control and turns to be positive after control in most regions, that is, the acoustic energy which is transferred into far field before control will flow to absorption structure after control.