There is no such thing as diaphramtic breathing. The diaphragm does not work that way.
All the choir directors and uninformed band teachers should be ashamed for saying "Use your diaphragm" to support the sound.
When we inhale, the diaphragm
pulls downward and the chest cavity expands,
pulling oxygen-rich air in through our nose
and/or mouth, down through the
tube connecting the mouth/nose with the
lungs), and into the lungs, where the oxygen
and carbon dioxide exchange takes place.
When we exhale, the diaphragm relaxes, the
chest cavity collapses, and the carbon
dioxide-rich air is pushed from the lungs,
through the trachea, and out through the
nose and/or mouth.
You cannot support the air flow OUT with your diaphragm as it is relaxing when we exhale.