The comments above about singing quietly to get people's atention fits with my experiance.I don't sing (well not very offtern)but I once sore a friend of mine silence an intire pub (session and punters) singing very quietly while playing the celtic harp, as others have said the silence expanded over 20 seconds or so to fill the hole space.The trick(if thats the right word) is to mean what you sing and give it 110 % commitment, people know magic when they hear it and usually shut up. All the best PP