I use a "Hudson" type pump up garden sprayer. But first, I completely "tent" the room with plastic. 2" masking tape around ceiling wall line, insert plastic under tape. Tape down and cover the floor with plastic too, double layer, as you will want to pull it all down and roll it up after it is scraped. (it will be messy).
Use the garden sprayer to completely soak the ceiling surface with water, let it set for about 20 minutes. Then completely soak it again. Scrape it off with a 12' wide drywall blade, old acoustic should come off now in "sheets"because it is wet. After the ceiling is all scraped off, let it dry completely, then sand lightly (there will be "goobers" still left on the ceiling. (Make sure you wear a mask doing all of this).
It is now ready for whatever you want to do with it. The joints and nail spots may need to be "floated" with drywall mud (then sanded) unless you are going to apply a heavier type texture, otherwise if just painted you will see the joint lines and nail indentations.
If you want a texture on the ceiling, you can do this by spraying thinned drywal mud through a hopper and compessor (orange-peel texture) or hand applied (plaster type) also done with thicker drywall mud.
It is also important to know that asbestos was used in the "cottage cheese" type texture until 1973 when the formula was changed. So if your house is older than 1973, be careful of breathing the "dry" dust.
I am a drywall contractor and have done this stuff for 29 years.
Good luck