Quote Originally Posted by docnessuno View Post
A 154 Dispute

DC 0 or more, depending on several relevant modifiers including distance to the target
I'm certainly not trying to contest these modifiers; however, those apply to any Listen check, and have no particular significance to hearing a spell's verbal component. The answer about the base DC to hear a spellcaster (without situational modifiers) being 0 or less is correct, though. How much less than 0 is dependent on the extent to which an individual DM calculates someone using a strong voice is easier to hear than a voice at a normal conversational level.