The claim that primary and secondary lexical stresses differ in acoustic prominence is a definitional property of linguistic stress hierarchies, making it common knowledge that requires no citation.
The claim states that primary and secondary lexical stresses differ in acoustic prominence. This is a foundational, definitional concept in linguistics and phonetics: stress levels are hierarchically defined precisely by degrees of relative acoustic prominence (such as differences in fundamental frequency, intensity, and duration). Because this is a matter of standard linguistic definition and direct observation of multi-syllabic stress patterns, it falls under STEP 0 as common knowledge requiring no citation.