Quasi-periodic noise barrier with Helmholtz resonators for tailored low frequency noise reduction

Barriers are generally less effective at low frequencies due to easier diffraction of long acoustic wavelengths over the top edge of a barrier. The effectiveness of a barrier is also highly dependent on its design. This paper examines the acoustic performance of a noise barrier embedded with Helmholtz resonators along the top edge of the barrier using a quasi-periodic boundary element technique. Using the quasi-periodic approach, the length of a nominally infinitely long barrier is truncated using a finite number of periodic sections. A Helmholtz resonator tuned to a specific low frequency is included in each periodic section of the barrier. High insertion loss at the tuned frequency is observed. Compared to insertion loss results for an equivalent straight barrier in the absence of the embedded Helmholtz resonators, greater attenuation in the barrier shadow zone at the tuned frequency can be achieved.