Perforated plates are very good at attenuating sound in the duct systems, especially treating HVAC duct systems where private conversations are conveyed to next room. Perforated plates should be mounted vertically or horizontally in the duct to reduce the sound transmission. A novel analytical model that takes into account the effect of perforations and the effect of the flexural vibrations in the plates has been formulated and used to calculate the insertion loss in the absence of air flow. The agreement between measured and predicted insertion loss of perforated porous plates in the absence of air flow is satisfactory.
Aygun, H., & Attenborough (2008). The insertion loss of perforated porous plates in a duct without and with mean air flow. Applied Acoustics, 69(6), 506-513. https://doi.org/10.1016/j.apacoust.2006.12.007