An example with the Back to the Future clocks, with different colors of the text for each speaker, with location. They show date and time when the podcast originally aired.
Also in the radio station speakers could seat and show only the upper half of the body (easy to complete).
This picture is also accidentally nice for the characters staring at their creators (when they will be there ) trough the glass.
To emphasize the current speaker, as besmaller asked, the three (exceptionally four) spotlights could be used. When a speaker talks, the spotlight above him becomes brighter.