By default, the built-in microphone on an iMac computer is on and available for any programs that need to use it. You have the option of disabling the built-in microphone by changing the audio input from the microphone to the audio port. The iMac can only utilize one audio input at a time, so doing this disables the microphone.
Instructions
1 Open the "Apple" menu and select "System Preferences."

2 Click on the "Sound" icon in the "System Preferences" window.

3 Select the "Input" tab on the top of the "Sound" window.

4 Click "Line In" to select it as the device. The internal microphone is disabled.

TAGS:radio microphone, microphone