![]() These audio signal transformers are called “matching transformers” and couple the load to the amplifiers output as shown below. Signal transformers are used to match the loudspeakers higher or lower impedance value to the amplifiers output impedance to obtain maximum sound power output. ![]() One very useful application of impedance matching in order to provide maximum power transfer between the source and the load is in the output stages of amplifier circuits. Well, there are loudspeaker impedance matching transformers available that can change impedances from 4Ω to 8Ω, or to 16Ω’s to allow impedance matching of many loudspeakers connected together in various combinations such as in PA (public address) systems. During the maximum power transfer the efficiency Pmax/P×100 V02/4RTH/V02/2RTH 100 50 Steps to solve a network using maximum power transfer theorem Step 1-First remove the load resistance and find Thevenin equivalent resistance RTh of the source network looking through the open-circuited load terminals. But how could you impedance match an amplifier and loudspeaker which have very different impedances. Improper impedance matching can lead to excessive power loss and heat dissipation. Connecting two 8Ω speakers in parallel is equivalent to the amplifier driving one 4Ω speaker and both configurations are within the output specifications of the amplifier. Then if the 8Ω speaker is attached to the amplifiers output, the amplifier will see the speaker as an 8Ω load. The output impedance, Z OUT of the amplifier may be given as between 4Ω and 8Ω, while the nominal input impedance, Z IN of the loudspeaker may be given as 8Ω only. One good example of impedance matching is between an audio amplifier and a loudspeaker. This is called a “matched condition” and as a general rule, maximum power is transferred from an active device such as a power supply or battery to an external device when the impedance of the external device exactly matches the impedance of the source. ![]() From the above table and graph we can see that the Maximum Power Transfer occurs in the load when the load resistance, R L is equal in value to the source resistance, R S that is: R S = R L = 25Ω.
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