a mashup from two other things:
seashell - http://www.thingiverse.com/thing:417402
ipad sound - http://www.thingiverse.com/thing:16140
I added a "spring" inside so this should fit with and without a cover on your iPad2 and later. If it fits iPad earlier, let me know.
Added a second one that has a thicker shell which prints more easily.

Printed on a Dreammaker Overlord Pro. I used Blender to mash two objects together for a nicer look to the iPad amplifier.