Custom Angular directive broadcasting an event but not to nested children?

I have created an accordian directive in Angular which can be nested, so an accordian can have child accordians inside them.

I want to broadast an event when the accordian opens and closes so that other directives can listen for it (e.g. a menu inside an accordian panel might reveal itself when the accordian it's inside is opened).

The thing is that if there is a nested inner accordian inside the outer one I don't want the event to be broadcast to the inner accordian's child elements because the inner accordian hasn't broadcast an open/close event.

Just in case that makes no sense, to put it another way an element inside a nested accordian should be able to listen to an open/close event broadcast by the accordian it is in, not the one further up the DOM tree.

Hopefully there is a simple solution to this.