Well, I have worked a few times at Galaxy, three classical music recordings, but with my own gear. I was indeed impressed by the level of isolation they have there, you can be recording pppp pizzicati on a solo viola, while they are mixing 130dB heavy metal in the nest control room - and hear nothing
But the control rooms are too dry for my taste, while they are sounding very good and must be the most comfortable and accurate room I have ever been in on a location recording
So, that was a first design decision, not going for a totally controlled environment, but something that gets closer to an ideal end-user listening room.
I did meet Eric Desart once, to talk about my project, but the timing was completely wrong, because I had to finish the private part of the house first. And of course, we did not completely agree. I am quite a stubborn man
That brings me to the first decision, the two leafs for the walls. The outer leaf was decided with the rest of the house, cellular concrete blocks (Ytong, 100 Kg/m2, 24cm thick), because of the thermal insulation and reasonably good acoustic properties. Eric was concerned by this and advised me using something heavier around the studio, but the walls were already being built at the time. He was afraid the coincidence dip if the outer and inner leafs would be quite bad, but this seems to have worked out very fine. That was the main reason I decided to go for something much heavier for the inside, ie Silka blocks (270 Kg/m2, 15 cm thick). At the same time I found a Canadian study online (sound transmission loss measurements through 190mm and 140mm blocks with added drywall and through cavity block walls), with a measured STC of 79 for a 190/90 wall with 155mm cavity and 65mm glass fibre. the interesting part is where they measure a 90/90 mm wall with 115mm cavity and 65 mm of fibre glass, loosing only 2 dB of STC ! These measurements are of course with one wall on a floating assembly, so no flanking noise. The same wall on one slab gave 15 dB worse STC !
But the most clear thing is the complete absence of coincidence dip, and around 42 dB of isolation at 63 Hz.
So I based my walls (with 100-120 mm cavity) on this study, just a gut feeling, because I am using other materials, but very probably better. To make sure, I asked for test reports on single leaf walls, both for Ytong and Silka.
And the main goal after that was making as little errors and leaks as possible, finding a ceiling that would be up to scratch, and making a decent room and door. Don't forget, all of this is on a 16 cm concrete slab, on sylomer strips, calculation done by Getzner themselves.
I hope that answers your question
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