Broadband noise attenuation using a variable locally reacting impedance.

ABSTRACT

Passive control of low-frequency duct noise remains a technical challenge. Traditional noise control devices are either overly bulky or too narrowband. A broadband attenuation mechanism inspired by the mammalian cochlea is presented in this theoretical study. It consists of a parallel arrangement of an array of multiple beams or stretched strips backed by a cavity. The structure vibrates strongly in response to the broadband incident noise and hence creates substantial reflection. If both the media in the cavity and the duct are air, the mass-like load from the fluid in the cavity suppresses the response of the structure and thus lowers the transmission loss. If helium, or some other gas with lower density than air in the duct, fills the cavity, the mass-like reactance of the cavity is reduced and the silencing performance is improved. Then such a silencer can achieve a satisfactory attenuation performance at low frequency range. Multiple adjacent resonant peaks are found in the transmission loss curve and such a silencer has superiority in size and acoustic performance over expansion chamber and duct lining.