John. From the Crown page that links to the calculator:
"The calculations discussed here apply to anechoic or outdoor conditions. If the sound system is inside a venue, the room reverberation will increase the SPL typically by 6 dB. You can use this room gain as extra headroom."
While they don't explicitly include the adjustment in their calculator, they are certainly very clear that room gain needs to be taken into account.
I still think the page linking to the calculator is excellent. It was the first place I found that all the elements relating to power requirements were gathered together in one tidy package.
As to the numbers I originally posted using the calculator, that was operator error (me), not an inacurate calculator. A separate box for room gain would simplify the calculator though.
