PHP Code:
Callback_PlayerConnect()
{
     
level notify("connected"self);
    
     if(!
level.splitscreen)
          
iprintln(&"MP_CONNECTED"self.name);

     
self iprintlnbold("Welcome to X mod"); //put your message here
     
wait(0.5);
     
self playlocalsound("YOUR_WELCOME_SOUND"); //put your sound here

I just remember this thing but i didnt tested it, so i dont know if is working