What is the fundamental difference between head voice and falsetto in male singers? I think I know the answer, but I cannot be sure in its credibility, since all my self-researched knowledge comes from YouTube video lessons, internet articles, and the like. I also heard some very strange views on falsetto from people who have been supposedly studying music, that's why I would like to get a clear answer.
As far as I am concerned, the difference is in cord closure: that is, in head register the vocal cords are zipped up, leaving a narrow opening to vibrate, whereas in falsetto the vocal cords burst open. That's why we can hear a "flip" when a singer accidentally drifts into falsetto, because of this sharp change in chord coordination. Sound-wise, falsetto has an "airy" sound, and it usually starts with some "-h-h-h-" hiss before you can produce the actual note. Head voice, in contrast, has a clear ringing tone, it can also be produced at higher volume than falsetto. Even with my very limited vocal range, I can sing a light "-i-i-i-" with cords connected and easily start adding more volume, whereas when I sing it in falsetto, it's very quiet and "hissy" (although I can "hiss" higher notes in this register).
Please correct me if I got something wrong. As a case study, may I suggest "Somewhere Over The Rainbow" by Israel Kamakawiwo'ole, which, apparently, everyone considers to be sung in falsetto, but I have my own doubts, as it sounds rather "connected" at times (you can listen to the song here). Any other (better) examples would be fine too.
I decided to add some references to online resources where I picked up the notion described above: