(3) The law of magnetism states that opposite magnetic polarities attract, and like polarities
repel each other. As a result, when alternating current in the form or configuration of an audio signal
passes through the coil conductor, it interacts with the lines of force emanating from the permanent
magnet. The conductor is alternately attracted and repelled, so forward and backward movement is
created in accordance with the audio signal.
b. In most speakers the conductor is a wire coil and is attached to a cone that moves with it,
pushing and pulling at the adjacent air surrounding it. Basically, you have just learned the classic
operating principle of most speaker designs (fig 5-6).
Figure 5-6. Changing field of voice coil causes oscillating movement relative to constant field of
magnetic structure creating sound
Impedance. Impedance is the resistance to the passage of alternating electrical current. In the
past, high-fidelity components were not as standardized as they are today, thus, making the input
impedance of a speaker and the output impedance of an amplifier fairly critical to ensure they match.
Today, most equipment is rated uniformly at an average of 8 ohms. Eight ohms is said to be average
because impedance varies with the frequency of audio signal.