This and one of its sibling comments make a good point - maybe this would partially cancel the sound being reflected by the solid part of the wall. We can enter

This and one of its sibling comments make a good point - maybe this would partially cancel the sound being reflected by the solid part of the wall. We can entertain the possibility, because we know sound in air generally reflects from a wall in the same phase in which it arrived. (If it was reversing itself we'd be in trouble again.)