If you're talking about sound:
* Loud
* Noisy
* Sonorous
* Boisterous
If you're talking about speech:
* Vocal
* Talkative
* Loquacious
* Chatty
If you're talking about someone's personality:
* Outgoing
* Talkative
* Gregarious
* Sociable
Choose the best antonym based on the specific situation.