变压器用在报警喇叭上是什么作用？普通的喇叭不是这样用的

贴图出来

此時無聲勝有聲！

A typical high-impedance system is shown in Figure 1. A transformer at the power-amplifier output steps up the voltage to approximately 70 volts at full power. Each speaker has a step-down transformer that matches the 70V line to each speaker's impedance. The primaries of all the speaker transformers are paralleled across the transformer secondary on the power amplifier.
ADVANTAGES OF 70V OPERATION
As stated before, a 70V line reduces power loss due to cable heating. That's because the speaker cable carries the audio signal as a low current. Consequently you can use smaller-gauge speaker cable, or very long cable runs, without losing excessive power. Another advantage of 70V operation is that you can more easily provide the amplifier with a matching load. Suppose you're connecting hundred of speakers to a single 8-ohm amplifier output. It can be difficult to wire the speakers in a series-parallel combination having a total impedance of 8 ohms. Also it's bad practice to run speakers in series because if one speaker fails, all the speakers in series are lost. This changes the load
impedance seen by the power amplifier.