That's the way I'd do it. I was going to write something like that yesterday or the day before in a reply to you but then backed out. I started going on about calibrations and references and then found I was no help at all. But if you could generate a sine wave from a source and then reasonably assume that the levels were maintained when generating white or pink noise, then at least you would know you were close.What are you doing to set a reference for your microphone level? And are you measuring a meter away from the baffle, the dust cap, the horn mouth or diaphragm? Or are you going far away and then calculating back to get the W/M value?