Formal:
* Auditor: Implies a more official or critical listening.
* Hearer: A neutral term for someone who perceives sound.
* Recipient: Suggests someone who is receiving information passively.
Informal:
* Ear: A playful way to refer to someone who is listening.
* Soundboard: Someone who listens to and offers feedback.
* Attentive audience: Implies someone who is paying close attention.
Other options:
* Observer: Suggests someone who is listening and taking in information.
* Student: Implies someone who is learning from what they hear.
* Empath: Someone who can deeply understand and connect with the speaker's emotions.
The best word will depend on the specific situation and the tone you want to convey.