High frequency acoustic transmission loss of perforated plates at normal incidence

Abstract

A study has been conducted on the transmission loss of perforated plates at normal incidence. The investigation includes a theoretical analysis of the problem with validation through experimentation. The experiments comprised microphone measurements of transmission loss for 11 perforated plates with variable thickness, hole size, and porosity. The theoretical model is based on planar wave propagation through a single contraction/expansion chamber with modifications to account for hole interaction effects. The resulting formula for transmission loss yields superior predictions over past theories for the range of properties investigated. Deviations between experimental measurements and theoretical predictions of transmission loss are less than about 1.5 dB for dimensionless hole diameter d/λ < 0.5. The accuracy of the model does not show a strong dependence on plate thickness-to-diameter ratio or porosity.

Statistical Energy Analysis Model for Sound Pressure Level Prediction on Refrigerators

“…The total sound transmission is computed as the combination of 94 rectangular openings which are 8 mm in width and 0.457 mm thick. This hypothesis is sustained in the results presented in [33,11].…”

Normal incidence acoustic insertion loss of perforated plates with bias flow

“…The entropy fluctuations are not directly involved in the generation of true sound because acoustic fluctuations propagate at speeds corresponding to the sound velocity. 31 Phong and Papamoschou 1 showed that the end effects associated with the acoustic radiation from open ended tubes are an essential component in modeling the transmission behavior of perforated plates without bias flow. The end correction included interactions between the perforations in the form of a correction to the physical thickness of the plate.…”

“…The transmitted acoustic signal from our experiments were first scaled up by a factor of four to reflect the full-scale frequencies corresponding to the bleed valve application motivating this study. 15 The full-scale, narrowband power level spectra were then discretized into 1 3 -octave bands (see for example, Ref. 40).…”

“…In the linear regime of acoustic excitations, a perforated plate behaves as a lowpass acoustic filter when no mean flow is present. The transmission characteristics are determined by the perforated plate's physical parameters, 1 namely, the porosity, b, plate thickness, l, and hole diameter, d. The addition of bias flow through the perforations introduces potential benefits in the absorptive properties of the plate.…”

“…Without bias flow, dissipative effects are negligible for the transmission of small amplitude, high-frequency acoustic waves at normal incidence to the plate. 1 Additional losses in acoustic energy may occur when bias flow is present. The mean flow separates from the perforation rims, forming a shear layer.…”