Why are there 4 input terminals on some passive speakers?

Some premium speakers feature an input cup with 4 input terminals. These additional input terminals allow the speaker to be "bi-amped" or "bi-wired". 

Bi-amping - utilizing 2x amplifiers or amplifier channels to power a single speaker cabinet.

Bi-wiring - utilizing a bi-wire cable to connect a speaker with separate hi and low frequency inputs. 

-example of a bi-wiring cable below - the end that connects to the amplifier will have 2 connectors and the end that connects to the speaker splits into 4 connectors. 

NOTE: if your binding posts are labeled "Main" and "Height", they are NOT designed to be "bi-amped". These speakers have an additional "Height" speaker built in which will require a separate channel and set of wires. 

If you would like to bi-amp the speaker, you will connect one channel of a external power amp to the top set of terminals, and another channel of the external power amp to the bottom set of terminals. The top red and black terminals are for the high frequencies (Tweeter) and the bottom red and black terminals are for the low frequencies (Woofers).

If you are not bi-amping the speaker and would just like to connect it traditionally, then you will need the two metal jumpers that came with the speaker. The metal jumpers are simply a conductive medium to carry the signal between the two sets of terminals.

When using the metal jumpers, you will only need to wire into either the top, or the bottom, set of terminals. You do not need to wire into all 4 terminals since the jumpers are carrying the signal to both sets of terminals. It does not matter which set of terminals you wire into; wiring into the top or the bottom or one of each, is just fine.

Please note: If you no longer have the metal jumpers, or have misplaced them, you can use two small strips of standard speaker wire to achieve the same result. Again, you are just needing a conductive medium to carry the signal between both sets of terminals. The strips of speaker wire should be set exactly like the jumper bars are; black connected to black, red connected to red.