free download PNG images :Megaphone

A portable or hand-held cone-shaped acoustic horn, usually used to amplify a person's voice or other sounds and point them in a given direction. Raise the sound to the narrow end of the amplifier by raising the sound to the face and speaking to it, and then the sound waves are emitted from the wide end. The loudspeaker increases the volume of sound by increasing the acoustic impedance of the vocal cord, so that the impedance of the vocal cord matches with the air, so as to emit more sound power. It can also point sound waves in the direction the horn points. Because the frequency response of the megaphone is larger at a higher sound frequency, it will distort the voice sound.

Since the 1960s, these voice driven sound amplifiers have been replaced by electric amplifiers, which use power and folded horns to amplify voice.

Electric loudspeaker is a kind of hand-held public address system, which is an electronic device that uses electric power to amplify the human voice like a human loudspeaker. It consists of a microphone that converts sound waves into electronic audio signals, an amplifier powered by a battery to increase the power of the audio signals, and a loudspeaker that converts the audio signals into sound waves again. Although slightly heavier than acoustic loudspeakers, electric loudspeakers can amplify the sound to a higher level, more than 90 dB. In most applications, they have replaced loudspeakers and are often used to broadcast to people where there is no fixed public address system. In outdoor sports events, movie scenes, political rallies and street parades.