This one is harder as different genres will by nature be quieter. For me the one that was too quiet was Cracker years back, forget who opened, but my GF of the time wanted to see him, good as you couldn't hear him over the people talking.
And when Cracker came on, the audience was still louder than the band, until "Eurotrash Girl" where everyone sang along (poorly) and cheered.
That show sucked.