Connect your mobile to loudspeakers or Bluetooth speaker and your mobile will be converted into an announcement microphone.
Bluetooth speaker - Live Microphone send audio to bluetooth loudspeaker through your phone internal mic with the help of bluetooth connectivity. There is no need of wired while sending audio to bluetooth speaker. You can use this app as Realtime Mic .

Simply connect your mobile device to sound output device(Bluetooth) and use the app as a microphone.