air-gap or isolation ?

I´m building a recordingbooth with dubble walls.. I will have two layers of gypsum on the "out side"(control room) and one layer on the inside (recording booth). This means that i will have: 1 gypsum layer-isolation-airgap-isolation- two gypsum layers. My question is: Is it better to have 50 mm glassfibre in both walls with an 1/2 inch airgap or 30 mm in one wall & 50 mm in the other with a larger airgap. Thanx in advance !! Great forum !!!!!!!!!!! :D Sarza73

When calculating the airgap between the two walls (Drywall leafs), remember that the fibreglass is considered a part of that airgap being that it is not a SOLID material such as the gypsum board. I would double up on the gypsum in the iso booth with a different thickness though to realize a better STC And Density is the key to the glassfibre being most effective. We recommend using Mineral Wool or AFB as it is called here in the states instead of glass fibre. I hope that answers your question. Bryan Giles

Thanx ! I will add another gypsum layer and keep the 2 x 50 mm glassfibre then. Sarza 73