Low frequency attenuation of acoustic waves in a perforated pipe

This paper presents new experimental and numerical evidence that perforations in a pipe wall result in a low-frequency bandgap within which sound waves rapidly attenuate. These perforations are modelled as an acoustically soft boundary condition on the pipe wall and show that a low frequency bandgap is created from 0 Hz. The upper bound of this bandgap is determined by the dimensions and separation of the perforations. An analytical model based on the transfer matrix method is proposed. This model is validated against numerical predictions for the pipe with varying perforation geometries. A numerical study is undertaken to model the effect of perforations with ideal acoustically soft boundary conditions and surrounded with an air gap. Close agreement is found between the numerical and analytical models. Experimental evidence shows that the width of the bandgap is accurately predicted with the numerical and analytical models.

Automated summary

This paper presents new evidence, both experimental and numerical, that demonstrates the creation of a low-frequency bandgap in a pipe wall due to perforations, where sound waves attenuate rapidly. The perforations are modelled as an acoustically soft boundary condition, leading to the formation of a low-frequency bandgap starting from 0 Hz. The upper limit of the bandgap is determined by the dimensions and separation of the perforations. An analytical model based on the transfer matrix method is proposed and validated against numerical predictions and experimental evidence.