@Fat Boy Kyle. I -think- you're referring to the girl from that anime to aru something? If you are then I think the floating doll was done by an electro-magnetic field. If you're not, then ignore me xD

Making the air beneath the object more dense will probably work; I mean iirc acoustic levitation is exactly that, only with sound waves. It's just that I know so little about all this science bit and I was hoping I would be able to get a mentor or someone similar from here that I can [s]bug[/s] ask about. Regardless, the whole point of acoustic levitation was to find a levitating power which does not use electromagnetic waves.