It seems appropriate to apply these rules to voiceless consonants.

Literal

Voiceless consonants [to-に] these rules [object-を] apply [nominalizer-こと] [topic-は] appropriate [quotative-と] is-thought.

Academic linguistics register. 無声子音 = 'voiceless consonant' (phonology term). 思われる is the passive 'is thought' — used for a generalized or impersonal opinion, avoiding directly asserting it. Common in academic writing.