When the vocal folds come together they close off the windpipe. When you are breathing quietly they relax to the sides and leave an opening for the air to pass through. During speech or singing, the cords tense and flutter in the breeze, so that the airstream comes through in little puffs as the cords open and close. Like the onion skin fluttering in a kazoo, this creates the basic sound, a sort of buzz that vibrates the air above. The speed of the flutter determines the pitch.The vocal cords cross the windpipe in the throat (opening horizontally) just as the lips cut across it at the front of the mouth. When you make a lip buzz (“raspberries”), your lips are doing the exact same thing that the vocal cords do in creating a pitch. There’s a little tension from the lips – not too much – and a lot of air to force them apart repeatedly.
An important thing to keep in mind when you are singing, however, is that any feeling of effort in the throat is coming from the outer muscles surrounding and supporting the larynx. This kind of muscle tension only interferes with the efficient functioning of the
vocal folds. When the folds are working freely, the most you should feel from the throat is vibration.