In the simplest PA system setup possible, you would have a power amplifier with one speaker output connector and you would connect one speaker to it. Boom. Done. Some power amplifiers have two independent speaker output connectors. In this case you could connect one speaker to each connector. Again, boom. And twice the sound!
But what if you need to connect more than one speaker to a single speaker output connector on your power amplifier or powered mixer? If you have just a single speaker output, it would be nice to be able to connect two speakers to it, one for each side of the stage. Even if you have two independent speaker outputs available, you still might want to have an additional speaker or two further back in the audience, in addition to the two “mains” flanking the stage.
But where do we connect the additional speaker(s)?