A device that converts one form of energy into another form. A loudspeaker is an electro-acoustical transducer.
"Just a note to tell you how happy I am with the laser transfer of the three-78 rpm album of Fibber McGee and Molly on the Night Before Christmas. This dates from 1945, and has been part of every Christmas celebration in my family ever since, so it has seen some use. Cassette copies are played in my sons' homes on Christmas Eve, and enjoyed by ..."