It depends on room size (listening distance), listening volume, dynamic requirements and speaker sensitivity. Those are exactly the variables you enter into a calculator.
One of the major flaws with this calculator is that room size and listening distance are not the same thing. How can listening at 4 meters (13 ft.) outdoors be the same as listening at 4 meters in a 2500 cu. ft. room?
That is exactly why you add 4- 6 db for room gain.
I do not claim that this calculator is the be-all end-all definitive answer. It is a good guideline. If the calculator shows you are close to the limits of the receiver it may be worth while considering outboard amps. If, like me, you are only at the 60% mark of power available, outboard amps are a waste.
