megaphone

right|thumb|A megaphone thumb|An electric megaphone is used at a protest (Black Lives Matter, July 2021) thumb|An electric megaphone is used at a protest (Fight Trump, February 2018) thumb|A small sports megaphone for cheering at sporting events, next to a 75 mm cigarette lighter for scale

A megaphone, speaking trumpet, bullhorn, blowhorn, or loudhailer is usually a portable or hand-held, cone-shaped acoustic horn used to amplify a person's voice or other sounds and direct it in a given direction. The sound is introduced into the narrow end of the megaphone, by holding it up to the face and speaking into it, and the sound waves radiate out the wide end. A megaphone increases the volume of sound by increasing the acoustic impedance seen by the vocal cords, matching the impedance of the vocal cords to the air, so that more sound power is radiated. It also serves to direct the sound waves in the direction the horn is pointing. It somewhat distorts the sound of the voice because the frequency response of the megaphone is greater at higher sound frequencies.