Complex sentence: In a Polish consonant cluster, including across a word boundary, the obstruents are either all voiced or all voiceless, depending on whether the last obstruent in the cluster, excluding "w" or "rz", is normally voiced or voiceless.
Split into simpler sentences: In a Polish consonant cluster, including across a word boundary, the obstruents are either all voiced or all voiceless. To determine (based on the spelling of the words) whether a given cluster has voiced or voiceless obstruents, examine whether the "last" obstruent in the cluster, excluding "w" or "rz", appears to be voiced or voiceless.