Basically what I would suggest is add 4 functions for voice chat.
Whisper - Travels one tile - useful crowded/trading areas
Normal - Travels 3-5 tiles - useful indoors
Shout - Travels 10-15 tiles - useful in the fields and for guards
Speech - Special function only accessible from a podium to be used for speeches, performances, etc.. travels a customized distance up to 100 tiles
It could be made an option for the area within a claimed land that only players who are granted access are able to shout, or alternatively players could make it against the law for anyone other than guards to shout within the walls(disturbing the peace).