Silence

Area 
Creates an area of quiet. No one within this area can hear anything, and nothing that happens in this area makes any sound. It is the area that is affected and not the people in it; anyone moving out will be able to speak. 
Note that an area of silence will prevent spoken spells from working!

Duration: 1 minute. 
Base cost: 2 to cast. 1 to maintain. 
Prerequisite: Sound.

Item 
An area can be permanently silenced; the spell is on the floor or ground, and is broken if that area is torn up. Or a large rug can be enchanted for a portable silent area.  
Energy cost to create: 80 per yard radius, but only one spell is required for  the whole area.