I've always heard the pair should be oriented as Jim has shown, but I've never seen an explanation. It may depend on the tweeter and crossover frequency--I assume you would want the side with the smoothest off-axis response to be next to each other. I think that's the case with the ST, but I'll have to check again. I also have a feeling it doesn't make a lot of doo-dah difference. But then I never do. dah.