I am working on developing head voice / falsetto and am having an issue when attempting to sing ah vowels. I can get a clear, bright tone when singing ee or oo, but when I switch to an ah vowel the sound breaks down into a fluttery, fluty sound that seems like my vocal cords are not closing. I used to be able to get this sound without problems when I was younger, but I neglected my falsetto for many years and now this is an issue. I have been trying exercises moving from ee to oo to ah and doing them with less breath / volume in an effort to strengthen this area, but it's coming along slow. Does anyone have any suggestions? Ultimately I am trying to develop my mix voice to increase range and understand this is an essential step in that process.