Be serene, composed, polite or cordial, even in vigorous disagreement. Do not let your voice rise or fall but keep it modulated and reasonable.
If others listen then you may speak as loud as is necessary to be heard, no louder.
If a dialogue becomes of intense interest it should be deferred to a later date in a larger assembly room.
If you do lose composure you should apologise and defer the dialogue until you have had time to regain it.