Impedance is the measure of opposition to alternating current in an electrical circuit. It is similar to resistance but accounts for reactance in addition to resistance. Impedance is represented by the symbol Z and is measured in ohms.
For amplifiers and loudspeakers, impedance matching is important for maximum power transfer and to avoid damage. Here are some key points:
- Amplifiers have a rated output impedance, often very low like 2-8 ohms. Speakers also have a rated impedance, commonly 4, 8, or 16 ohms.
- For optimal power transfer, the amplifier output impedance should equal the speaker impedance. If the speaker has a lower impedance than the amp rating, it can overheat the amp.
- Connecting multiple speakers in parallel decreases the overall impedance seen by the amp. This lower impedance can overload the amplifier if not careful.
- Speaker impedance also varies with frequency. There are minimum and maximum points. The amplifier must be able to handle the full range.
Mismatched impedance can cause distortion, reduced power, or even damage to amplifiers or speakers in severe cases.
- Impedance mismatch losses are proportional to the square of the difference in impedance. Even small mismatches should be avoided.
- Transformers or direct boxes can be used to better match impedances between amps and speakers.
So in summary, matching the rated impedances of amplifiers and speakers is important for performance, efficiency, and equipment longevity. Engineers should understand speaker impedance curves and use best practices to avoid issues.