Alright, now I think I'm getting it. At 15" width, optimum height, based on the Golden Ratio, should be around 25-1/2".
1. How would we calculate depth at this point?
2. Would the back panel be of the same dimensions as the front?
I ask Question #2 because the article I read mentions that sides should ideally be not parallel to each other to avoid bouncing waves within the box. But it didn't discuss anything beyond that.