cylindrical wave उदाहरण वाक्य

My questions : a ) how is the result " loudness decreases with the ratio 1 / ( 2 ^ 0.6 ) r = 1 / 1.516r to the distance " obtained and is it correct ? b ) Is " loudness level " as described on that webpage the same as how subjectively loud a sound-noise is measured in db ? c ) What would sound intensity be in layperson's terms if it is not subjective loudness ? d ) Elsewhere on the page a " cylindrical wave " is mentioned.