Most sound sources emit mechanical vibrations in all directions. Only a small part of them reaches the listener. You can increase the efficiency of a sound emitter by making it directional. Then it will be heard at a considerable distance with a relatively low power.
Instructions
Step 1
The most common means for directing sound today - the horn - was invented before our era. It does not amplify sound, but only concentrates it, just as a parabolic reflector concentrates light. To make a horn, make a hollow truncated cone from any light sheet material, having a length of about 300 mm, a small diameter of about 30 mm, and a large diameter of about 200 mm. Provide a handle for ease of use. Such a simple device, although it does not compare in efficiency with a megaphone, will come in handy for the leader of a camping trip, a counselor in a children's camp, a coach.
Step 2
Just as the same lens can be used in both a projector and a telescope, the same horn can be used for both directing and capturing sound. Lean the small hole of the device not to your mouth, but to your ear, then direct it to the source of a quiet sound, and you will hear it much more clearly.
Step 3
The only way to improve the efficiency of a horn is to increase its size. From this it becomes cumbersome. To avoid this, make the device curved. Such horns, sometimes built into chairs, have been used in the past as primitive hearing aids. They worked effectively, but were not portable. Also curved horns are essential attributes of old gramophones.
Step 4
Try leaning a loudspeaker of the correct size against the small opening of the horn. Those on the sides will feel that the sound has become quieter, but those who sit in front of the large hole will feel the volume increase. This is also not an increase, but only a redistribution of energy in space. The first horn loudspeakers also used curved tubes - this solution is sometimes used today, but for decorative purposes. Loudspeakers with folded horns are more common. Such a device consists of a loudspeaker with a small horn directed inside the large one. The latter, in turn, is directed to the listener. Take a closer look at a megaphone, a loudspeaker on a pole, a police car and you will see just such a structure.
Step 5
But sound can be directed not only with a large horn. The phenomenon of beats between oscillations is observed in relation to both electromagnetic and mechanical waves. Directing ultrasound will require a much smaller horn than directing audible sound. Imagine two ultrasonic emitters directed at one point, one of which operates at a frequency of 30,000 Hz, and the other at a frequency of 30,500 Hz. Then, due to the beats, a person at this point will hear a sound with a difference frequency of 500 Hz. If you are into electronics, try repeating this experiment using generators and piezoelectric emitters no more than 10 milliwatts.
