How Phonographs Work
A phonograph is a device that reproduces recorded sound is called a phonograph or 'gramophone' and it was invented by Thomas Alva Edison in 1877. His model consisted of a metal cylinder covered with tinfoil which was mechanically rotated.
When the inventor spoke into a mouthpiece a diaphragm vibrated. This diaphragm was connected to a needle which rested on the metal cylinder. The vibration of the diaphragm caused the needle to quiver, so that the original sound was permanently impressed on the tinfoil as a zigzagging groove. The needle was later traced over the path of this groove so that the sound was reproduced.
Edison's principle has been utilized in all subsequent phonographs, although the quality of sound reproduction has been immeasurably improved since Edison's first scratchy rendition of 'Mary had a little lamb'. The cylinder was soon replaced by a flat, circular disc which was rotated on a turntable. During the boom years of the 1920s mechanical phonographs were gradually replaced by electric machines.
Electronics has enabled great advances to be made in phonograph technology. The modern needle, or stylus, incorporates a hard-wearing diamond or sapphire tip. The stylus is held in a cartridge which is suspended on the end of a finely balanced arm. Modern record discs are made from a durable, flexible plastic. The sound is etched into a continuous groove that runs in a spiral from the perimeter of the record to the center. The vibrations of the stylus are electronically amplified and then converted to sound waves in a loudspeaker. A high-quality loudspeaker contains bass, middle range and treble speakers in order to duplicate the original sound with great accuracy.
Most of the recordings made today are stereophonic. A stereo recording is made on two separate channels. The sounds from the two channels are delivered to the listener through a left and a right speaker to give the effect of three dimensional sound. A recent innovation is the quadraphonic system. It has four channels instead of two and the final sound is presented through four loudspeakers.