In electronics, impedance matching is about connecting two electrical systems of which the impedances differ. Some audio devices use transformers for impedance matching.
The concept of impedance matching is also used in optics.
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Basic schematic for matching R1 to R2 with an L pad. R1 > R2, however, either R1 or R2 may be the source and the other the load. One of X1 or X2 must be an inductor and the other must be a capacitor.
Typical push–pull audio tube power amplifier, matched to loudspeaker with an impedance-matching transformer