Last year I tried out for a Barbershop Quartet and they had a professional German voice instructor present. Since all I could sing was "folk" (nasal intonation and all), she cleverly pointed out how not to sing. Apparently, you should keep you feet apart, bend slightly, and use the diaphram for force the air over your vocal chords (rather like US Drill Sergeants); this relieves the pressure on the vocal chords. With practice it works, but I've given up on Barbershop Quartets for now ...

Cheers,

Brian