Wave propagation in acoustic ducts with periodic side branch resonators

Resumo

This paper presents the behavior of an acoustic duct with periodic side branch tube resonators commonly

used as a noise control device, which can be tuned to enlarge the resonance bandwidth and improve the transmis-
sion loss. An interesting approach to obtain a broader attenuation range in a duct consists in to distribute side

branches tubes resonators periodically along the duct. This generates some frequency bands, known as bandgaps,
where harmonic waves do not propagate. Bandgaps are generated based on the special frequency of mismatched
impedance areas which produce Bragg scattering (destructive acoustic interference) and local resonance effects
from the duct-tube system. This work investigates bandgaps created in duct-tube system using acoustic transfer
matrix method and finite element models. Numeric results are presented as dispersion diagrams, sound pressure

level and transmission loss. These results are discussed and compared with each other. Periodic geometry varia-
tions of the side tubes are also investigated.