A audio output device is NOT required during the exam (the proctors will not address you via voice, only via text chat). In the compatibility test, it is offered to listen to the recording so you can ensure that your microphone is working correctly.
The microphone is required to capture any potential in-room noise/conversation/etc and ensure the exam occurs according to the rules.
Yes, speakers are not needed, a mic is mandatory. Make sure the mic works by observing the red bars/indicator in the sound settings. Adjust the mic sensitivity by the slider...Do not move it fully to the right. It would just buzz