Anatomy Question

Is there a way to disable someone's voicebox, while still allowing them to breath, short of a laryngectomy?

The character responsible for bringing this up is something like a Torture Technician who makes house calls; the method doesn't have to cause permanent damage, but it should at the very least be excruciatingly painful (preferably impossible) to talk more loudly than a whisper for several hours.

Shove a stiff tube down their throat?

Not quite what I was thinking of.

Also, I suspect that would probably trigger a gag reflex.

A Torture Technician wouldn't care about gag reflex. And a tube down the throat will indeed make it impossible to talk while it's in place and painful once it's removed.

I heard on Colorado Public Radio that there's a rare medical condition where a person's voice is barely audible (similar to Laringitis but permanent) which can be often be cured by specialized physical therapy. Essentially the muscles that control the voicebox become cramped or sprained. Whether it can be caused deliberately, I don't know.