Jamieson, Fausset and Brown on Isaiah 29:4

4. Jerusalem shall be as a captive, humbled to the dust. Her voice shall come from the earth as that of the spirit-charmers or necromancers (Is 8:19), faint and shrill, as the voice of the dead was supposed to be. Ventriloquism was doubtless the trick caused to make the voice appear to come from the earth (Is 19:3). An appropriate retribution that Jerusalem, which consulted necromancers, should be made like them!