Sound medium (5)
I believe the answer is:
radio
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">sound medium</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for radio that I've seen before include "Speech receiver" , "means of communication" , "Sound receiver" , "Electronic receiver" , "Receiving set" .)