(n.) A device to magnify sound, or direct it in a given direction in a greater volume, as a very large funnel used as an ear trumpet or as a speaking trumpet.

attenuator audio-frequency tube ballast regulator ballast tube beam-switching tube convertor current regulator damper detector discriminator doubler ear trumpet electronic hearing aid focus tube generator hard-of-hearing aid hearing aid iconoscope inverter limiter local-oscillator tube megaphone mixer tube modulator multiplier multipurpose tube multivibrator oscillator output tube phase inverter picture tube power tube preamp preamplifier pulse generator radio-frequency tube receiving tube rectifier tube regulator repeater speaking trumpet stethoscope transducer transistor hearing aid trigger tube vacuum-tube hearing aid