There was help on an earlier thread - for 27 D, the definition is 'Band' (from Baud). I don't know how the rest of the clue works.
29 Diols - dials with an 'o' instead of 'a'/one. I'm not sure how this one works either.
Have you remembered that it's the incorrect letters that spell out the scene of the action? 28 Across and the next couple of letters show you the 'Common' referred to in the title.