Mic is mandatory for the exam, speakers are not. In case your internal mic is not shown in the settings, it means the internal sound card is not supported. You may perhaps use the mic of the connected usb webcam or connect an external usb mic or a headset (the headset has to be placed on the desk, not allowed on the head). Than you switch the propper mic input in the drop down menu and adjust its volume (sensitivity) by moving the slider to the right so you can see the red bars moving as you speak and make some noise. I hope this answer helps.
Thanks for your reply, Indeed, I used the external webcam mic and it works perfectly Btw, I have just cleared the exam EX280, it is always special when we get a RedHat certification Thanks to the community.
