Sony introduced the first portable cassette player in the late 1970s. Its founder Akio Morita regularly travelled by plane and he wanted to listen to music. He asked his engineers to adapt a small journalist tape recorder to play back through headphones. He liked the design and the “Walkman” was born. The personal stereo or CD player is a popular item to carry around, for you to take music wherever you want. The disadvantage of the personal stereo is that it is difficult to share your music with your friends.
We all hear sound through our ears. A microphone works like our ears. It has a diaphragm that is vibrated by sound waves. The signal then gets encoded. When the signal is then played back through your stereo, the amplifier sends it to a speaker, which re-interprets it into physical vibrations. The speaker is therefore the final section of the translation circuit. It takes the electrical signal and translates it back into physical vibrations to create sound waves. Traditional speakers do this with one or more drivers. A driver produces sound waves by rapidly vibrating a flexible cone or diaphragm. The cone is usually made of paper and attached to the suspension. This is a rim of flexible material and it allows the cone to move. The suspension is attached to the basket, a metal frame in which the speaker sits. The narrow end of the cone is connected to the voice coil. The coil is attached to the basket by the spider, a ring of flexible material. The spider holds the coil in position, but allows it to move freely back and forth. The voice coil is a basic electromagnet. Running an electrical current through the wire creates a magnetic field around the coil. The audio signal from the amplifier causes the current in the coil to change moving the coil back and forth rapidly. When the coil moves, it pushes and pulls on the speaker cone. This vibrates the air in front of the speaker, creating sound waves.
For a speaker to work effectively it is important that it is housed correctly. If you simply placed a speaker on the table, the table would vibrate so much it would drown out a lot of the speakers’ sound. The speaker housing can effect how the sound is produced. The easiest method to use is to mount the speaker on a plate or baffle. You can see the effect of a baffle by cupping your hands behind the loudspeaker to form a simple baffle. The sound quality should improve and it gets much louder.