Similar in meaning:
* Aloud (spoken so that others can hear)
* Boisterously (loud and lively)
* Clamorously (making a lot of noise)
* Decisively (with force and certainty)
* Forcefully (with strong emphasis)
* Haughtily (in a proud and arrogant way)
* Noisily (making a lot of noise)
* Raucously (rough and loud)
* Robustly (with vigor and strength)
* Stridently (harsh and piercing)
* Vociferously (in a loud and forceful way)
More specific:
* Thunderously (like thunder)
* Shrillly (high-pitched and piercing)
* Belligerently (in a hostile or aggressive way)
* Cheerfully (with enthusiasm and happiness)
The best adverb to use will depend on the specific context and the kind of loudness you want to describe.