- “Could you please lower your voice?”
- “Please, make a little bit less noise. I know you probably don’t realize it but it is really disturbing”
- “I have trouble focusing while you are talking. I’d really appreciate if you could talk a bit further away”
… Usually, people do not realize how loud they speak, so they will probably appreciate an amiable reminder. Do it with a smile and it is almost certain that no one would be offended. Be direct and tactful, but never attack personally.