aërophone

from The Century Dictionary.

• noun An instrument having the functions of both an ear-trumpet and a speaking-trumpet.
• noun An apparatus invented by Edison for increasing the intensity (amplitude) of sound-waves, as those from spoken words.

from the GNU version of the Collaborative International Dictionary of English.

• noun A form of combined speaking and ear trumpet.
• noun An instrument, proposed by Edison, for greatly intensifying speech. It consists of a phonograph diaphragm so arranged that its action opens and closes valves, producing synchronous air blasts sufficient to operate a larger diaphragm with greater amplitude of vibration.