Second chakra (Sacral) - located about 2-3 inches below the navel. Tone seven times using a higher pitched but still deep "OOO", as in "you". (Orange).
Third chakra (Solar Plexus) - located above the navel. Tone seven times using a higher pitched "OH", as in "go". (Yellow)

from: http://destinydreamer2012.blogspot.com/2007/01/sanskrit-sacred-chakra-tonings.html