Window secondary glazing question-Acoustics Forum-Acoustic Fields Forum

Hi, wanting to maximise sound absorption at the windows of my home.

First some background context, secondary glazing refers to two separate window frames, providing a primary glazing at the outer face of the wall and a secondary glazing at the inner face of the wall, creating an enclosed space between the two panes. This compares with double glazing, which is usually a single frame with two panes of glass in it, sold as an integrated glazing unit (IGU). The panes of the IGU may be separated by argon gas, but they will be usually less than a 10mm apart. Secondary glazings are said to be better for low frequency sound due to the depth of the enclosed air, at least 100mm of enclosed space between the two panes of glass is recommended to have effect on low frequency sound. (Of course, the wavelength of 100Hz sound is 3432mm, so I question how much effect 100mm of enclosed space can have anyway). It is also noted that having slightly different thicknesses of glass on the primary and secondary glazings may help with sound absorption as the resonant frequencies will be different.

Now, my question, perhaps a silly question. Suppose primary and secondary glazings as described. Would it be better to use the thickest possible glass on the primary glazing (even an IGU), or would it be better to use thinner glass if it ensures a greater than 100mm enclosed space? To put it another way would two piece of thick glass with less than 100mm enclosed space be inferior to two slightly thinner pieces of glass with greater than 100mm enclosed space?