How Everything Works
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QUESTIONS AND ANSWERS
 
Question 606

What is the difference between a low impedance output and a high impedance output of an audio distribution amplifier? What kind of output does consumer equipment need? — JH, Eugene, OR
Some audio amplifiers provide several different outputs, each characterized by the impedance of its expected load (e.g., the impedance of the speaker that you should attach to that output). This impedance measures the relationship between voltage and current that the load needs to function optimally. The higher the impedance, the more voltage the amplifier must provide to propel a particular electric current through the speaker. If the speaker that you attach to the amplifier has the wrong impedance, the amplifier won't be able to deliver its maximum audio power to the speaker and you may damage the amplifier, speaker, or both.

Since a typical household speaker has an impedance of 8 ohms, you should connect it to an amplifier's 8 ohm output. However, if you connect more than one speaker to the same output, you should be careful to determine the combined impedance. For example, two 8-ohm speakers in series have a combined impedance of 16 ohms while two 8-ohm speakers in parallel have a combined impedance of 4 ohms. Many amplifiers are designed to accommodate these arrangements.

When a distribution amplifier must send current long distances through thin wires, it will often use higher voltages and lower currents to minimize power losses in the wires. Such an amplifier expects its load to have an unusually large impedance. In this situation, the speaker that is used must either have a large impedance, so that it can use this high voltage/low current power directly, or there must be an impedance matching transformer between the amplifier and the speaker.

         

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