Stancey Lapainte, age 13, of Nogales, Ariz., for his question:
HOW D0ES HI FI WORK?
Hi fi, or high fidelity, is a way of reproducing sound with the greatest possible fidelity or faithfulness to the original. Hi fi equipment may be used to reproduce any kind of sound but is most often used for music.
The basic parts of a hi fi system are a program source, an amplifier and a loudspeaker system. The program source can be a record player, an FM (frequency modulated) radio tuner or tape recording equipment.
In a record player, the pickup cartridge in the player's tone arm produces weak electric waves when the record makes the needle vibrate from side to side or up and down.
An FM tuner changes a radio broadcast into similar electronic waves.
Tape recording equipment changes magnetic patterns on a tape into electronic waves. To re create sounds from any of these program sources, the electric waves are connected to the amplifier, which is connected to the loudspeaker.
The first part of the amplifier that the waves enter is the preamplifier.The preamplifier strengthens the waves and has controls to adjust the volume and tone of the final sound. The other part of the amplifier, the power amplifier, makes the waves powerful enough to operate the speaker system. The speaker changes electric waves into sound.
In some hi fi systems, the preamplifier and power amplifier are separate components or units.
Most hi fi systems are sold complete and ready to play. But some people build the components separately and make their own hi fi system.
Transistors have helped manufacturers combine hi fi components. Transistors are small and they produce little heat. For these reasons, they eliminate the need for some large, heavy parts used in components once made with vacuum tubes.
Stereophonic hi fi gives realistic depth and clarity to sound reproduction.
When recording for stereo, or stereophonic hi fi,, engineers use at least two microphones to pick up the sounds made by an orchestra. They may place one microphone on the left side of the orchestra and another on the right side.
The sound waves picked up by the left microphone then make up the left stereo channel, and those picked up by the right microphone make up the right channel. The channels may be broadcast over FM stereo radio or recorded on stereo records or tape.
To reproduce both stereo channels, a hi fi system needs a stereo amplifier which has two amplifiers in one and two loudspeaker systems. One speaker system reproduces the left channel at the same time that the other speaker system reproduces the right channel.
Engineers have also developed four channel stereo, which reproduces musical echoes from the sides and rear of a concert hall, as well as the sounds coming directly from the orchestra. A hi fi system needs four amplifiers and four speaker systems to reproduce four channel stereo.