[Freeswitch-users] please help!!! playing tone only when 3rd party joins in bridging conference

[ran zhang]

I have a bridging conference established with 2 people in it, and i want 
to play a tone when 3rd party joins in. I can't set the conference's 
'enter-sound' to play the tone since it will play the tone when first 2 
people establish the bridging conference.