How a megaphone ampilifies sound?

Answer 1

Megaphones don't technically amplify sound. They redirect it into a smaller, more concentrated beam.

Sound naturally radiates in a sphere. Much of your voice energy, without a megaphone, will travel to the sides, up, and even behind you. This is not good if you need to shout to someone across a field, as most of the sound won't hit his ears!

A megaphone's sides kick these otherwise wasted sound waves back into play, and give them direction. It also combines these waves in sync, making them collectively louder.

Though a straight tube can "beam" your voice as well, the conical shape is more efficient, because it follows the natural propagation of sound (a cone is a slice of a sphere). If it didn't, the waves would bounce erratically, cancel each other out and add delay, leading to a diffused sound similar to reverb. You can try this with a long tube.

Also, a cone helps smooth the transition from a tight channel with a lot of bouncy resistance (your throat) to a large space with almost no resistance in all directions (the free air). This transition from tight to open will happen anyway whether you use a megaphone or not. But a conical shape gradually allows a wave to be more and more "free to move" over time, instead of violently popping it out of the end. A megaphone, therefore, is more like a gradual dive, and less like a belly flop.

Megaphones are long. To get good frequency response, a megaphone must be at least as long as the lowest wavelength you wish it to support. Why? Because the waveform must bounce against the side to get any benefit, but if it's too long, it'll escape the megaphone before it bounces! Therefore, if you want to support a middle C (261Hz, wavelength = 1.3 meters), the megaphone should be at least 1.3 meters long. To support the entire range of speech, it'd have to be about 4 meters long!

You may think a megaphone makes sound "bigger" because of its expanding shape. This is incorrect. It actually compresses sound into a smaller beam, sending more sound towards your target. The cone shape is used because it's less violent to the waves than other shapes.

Answer 2

A megaphone amplifies sound by directing and focusing the sound waves in a specific direction, allowing them to travel further distances. The shape of the megaphone helps to gather and project the sound waves, making them louder and clearer for listeners to hear. The design of the megaphone also helps to prevent sound from dispersing in other directions.

Answer 3

It projects sound waves and it bounces off the wide end.