On the speaker impedance

General audio equipment commonly cited impedance of loudspeaker impedance, pre-amp expanding machine input impedance, fore output impedance, (after the class is typically not called output impedance, and that output resistance), the transmission of the signal line blocking resistance (or characteristic impedance) ... ... And so on. Due to the impedance of the units still ohm, Ohm's law also applies, in short, in the same voltage, the higher will flow through the impedance less current, the lower the impedance will flow through the more current. The most common to the loudspeaker impedance of 8 Ohms is marked values, representing the trumpet in a factory test specifications, when input 1KHz of sine wave signal, it renders in eight-Ohm impedance value is, or is in the Horn of frequency response range, an average of impedance value. It is not a fixed value, but rather as the frequency. When after the class output a fixed voltage to the trumpet, according to Ohm's law, 4 ohm speakers than the eight-ohm speakers more electricity flowing through a times, theoretically, an eight-ohm output 100 Watt Crystal after the class, in four-ohm speakers connected automatically to 200 watts. When the speaker impedance value all the way down, after a fixed voltage level output, it will flow through the current increasing, in the end it seems a bit like the speaker cord directly short-circuiting, impedance values sometimes low-ohm, outside this range, the machine will be burned. This is generally used to say: after the level of power is not big, but the output current to big it is not truth.