Answer:
Vocal Quality.
Explanation:
'Vocal quality' plays a crucial role in ensuring the effective communication of the intended idea or thought of the speech to the audience as it is the voice that assists in creating the desired tone or effect in the speech and convey the idea in a manner that aids to elicit the desired response from the audience.
In the given example, Obi's 'vocal quality' is quite poor as he fails to present his speech topic in a loud, confident, and clear voice that not only ensures the effective delivery of the message to each and everyone in the audience but also create an engrossing effect on the audience that would compel them to believe in the claims presented. But he rather presents his ideas in a quite and mumble voice that is not audible to the audience properly and the lack of clarity approves the point that Obi is employing highly poor 'vocal quality' to present his speech.