Re: How does a magnet make a speaker work?

The principle behind an amplifying system is the conversion of sound waves into an electrical signal by an amplifier, which is then re-converted into sound waves by a loudspeaker. What we're looking to understand is how a loudspeaker works. As you already know, the basic structure of a loudspeaker consists of a coil of wire suspended in the gap of a cylindrical magnet, and a paper cone attached to the coil. The electrical signal (an alternating current) from the amplifier is transmitted through the coil of wire. This electrical signal causes a magnetic field to be set up around the magnet which varies with the polarity and amplitude of the electric signal. The magnetic field in turn acts on the coil of wire and causes it to move back and forth as the magnetic field varies. The paper cone vibrates as the coil moves and causes the volume of air contained in the paper cone to vibrate, thereby setting up sound waves. A big and heavy cone would set up low frequency vibrations, causing bass notes to sound, whereas a small, light cone would cause treble note to sound. A combination of factors would determine how good a speaker was. A few of these are the size of the cone, the mass of the moving system (cone and voice coil), the strength of the magnet and the efficiency of the system. All these factors are interlinked and have to be adjusted so that the optimum sound is obtained. The efficiency of the system (Q) is the ration of energy stored in the system to the energy lost by the system, and would be 1 for the perfect system. In addition, speakers manufactured by companies would have features such as filters to reduce the noise in the background when the signal is produced, a combination of speakers from woofers to tweeters for varying frequencies and others. I hope this answers your question. if you would like a more technical explanation, just let me know.