sound off vs speak out

sound off

verb
  • To hold forth about something in an opinionated manner. 

  • Command instructing a person to confirm that they are present or that some other objective has been met. 

  • Command instructing a person to speak up or acknowledge something. 

speak out

verb
  • To assert or promote one's opinion; to make one's thoughts known. 

How often have the words sound off and speak out occurred in a corpus of books? (source: Google Ngram Viewer )