You can obtain excellent benefits with only a 4mm glass, by having an air hole of 150mm it is possible to attain a 48dB sound reduction. Glass of all thicknesses should have this resonance frequency, so It doesn't matter how thick you go, there will always be a frequency https://secondary-glazing-for-noi02345.mybuzzblog.com/14398787/5-simple-statements-about-noise-control-secondary-glazing-explained