Sometimes a question is just not loud enough for you to hear clearly—maybe the audience member doesn't have a microphone or doesn't speak loudly enough at all times even with a microphone.
It's important to say when you don't hear all of the question asked (see scenario 2 if you heard the question but don't understand what is being asked).
At international conferences and in research meetings, we have often seen this miscommunication happen: the presenter doesn't hear the question well enough, so they respond with "Pardon?" or "Sorry, could you say that again?" and the asker wrongly assumes the presenter didn't understand the original question and then spends unnecessary time recasting the (sometimes lengthy) question.
A quick way to ensure the audience knows that you couldn't hear a question (rather than didn't understand it) is to say so explicitly.
When you didn't hear all or most of the question and need to hear it all again:
- Sorry, I couldn't hear that. Could you say it louder please?
- Sorry, I couldn't hear that very well. Could you repeat it a bit louder?
When you didn't hear part of the question well and want only that part to be repeated:
- Sorry, I didn't hear the last part of your question. Could you repeat that part again please?
- Sorry, I couldn't hear all of your question. Did you say/ask "xxxxx"?
- Pardon? I couldn't quite hear the last part of the sentence. Are you asking whether/if…?
As you say this, you can also signal non-verbally that you didn't hear, by tilting your head and shoulder forward slightly toward the asker.
Also, note that the common phrase "I didn't catch that" can be used to mean both "I didn't hear that" and "I didn't understand that." So, it's best to use the verb "hear" to make the problem immediately clear to the asker.