The sound of a boy is louder than a girl why

The sound of a boy is usually louder than a girl, because males usually have a larger Adam's apple, resulting in stronger vocal chords, and thus, stronger voice/louder voice

Explanation:

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Males have a lower vocal range than females, which makes their voice easier to hear than a girl's voice, which is often times at a higher vocal range with higher frequencies.

Explanation:

Lower frequencies (found in the voices of boys) are easier to hear than higher frequencies (found in the voices of girls)