你可以大聲一點嗎：
Could you speak up?
Could you speak louder?
（X）raise your voice = get angry
你可以小聲一點嗎：
Could you keep it (your voice) down, please?
Could you lower your voice?
（機器）調小聲：turn it down ； lower the volume
（機器）調大聲：turn it up ；raise the volume
Could you lower the volume? I am trying to study for my test tomorrow.
你可以小聲一點嗎？我要復習明天考試的內容。
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