Studio Doors/Do STCs sum?-Acoustics Forum-Acoustic Fields Forum

I’m starting a new build. I’ll have two walls back to back, separating my control room from my tracking room. The walls will be a minimum of 1′ apart at the narrowest point, and spread to about 3′ at the widest point. Instead of having a big window and doors, I’d like to use sliding glass doors (one for each wall)–I worked at Masterfonics in Nashville many years ago, and it seems to be a good two-birds/one stone solution.

My question is: if one door has an STC rating of 30, would the two doors together make a total STC of 60? (yes, I do realize that 30+30=60, but sound doesn’t always work so simply. . .)

The reason for my query is that I can get doors from “Really Expensive Studio Door Company” that has a total STC rating of 65 for $6k, OR I can get two doors from a company like Andersen that has specs for each door at an STC of 30+ for $2K. . .

Thanks!!