Voice box (6)
I believe the answer is:
larynx
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">voice box</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for larynx that I've seen before include "Source of squeaks" , "part of throat with vocal chords" , "The voice box, part of throat" , "it's essential to speak!" , "box for speaker" .)