Earth, Bridge, Link & Jumper Cables.
Link & Jumper Cables - Looking at the back of modern speakers, you will see four terminals; most of your speaker cables only use two per speaker. You will see a brass plate between the top and bottom; This is a bridge for the crossover. The crossover is a circuit board that sends signals to the higher-frequency speakers and the lower bass drivers. If you want greater resolution, clarity and better bass, change out the brass plate for a jumper kit and revel in the improvements. This is also a modern improvement to the concept of bi-wiring.
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