It appears what you have is a JL audio crossover for one of their component sets. Two of these come in the set, one for right, one for left. They limit the frequencies for the tweeters and midrange speakers. The markings for the terminals are as follows:
INPUT (+/-) - audio signal, high level, from radio's speaker wire or amplifiers output
W (+/-) - output to the midrange/midbass speaker
TW (+) - output to the tweeter's positive terminal
TW (-) REF - output to the tweeter's negative terminal, used as a reference for normal operation
TW (-) -2dB - output to the tweeter's negative terminal, but lowers the "volume" of the tweeter by 2dB, used if tweeter is too loud
TW (-) +1.5db - output to the tweeter's negative terminal, but raises the "volume" of the tweeter by 1.5dB, used if tweeter is too quiet
The side markings are as follows:
XO-2 2 way Crossover - model and description, 2 way means 2 frequency paths, i.e. high and low
Impedance: 4 Ohm - when hooked to a radio or amp it will be seen as a 4 Ohm load, same as speakers and subs
HI: 12dB/octave @ 5000 Hz - rate and frequency that the tweeter is "crossed over" at
-12dB/octave basically describes how well the crossover works, 12 good, 18 better, 24 best
-5000 Hz means the tweeter will not play anything below 5000 Hz
Tweeter Protection Circuit - means there is a circuit built into the crossover that protects the tweeter
Mylar Cap and Air-Core Coil - describes the material that the components inside the crossover are made of
LOW: 12dB/octave @ 5000 Hz - same as HI, but refers to the midrange, and instead of it playing everything above 5000 Hz, it plays everything below 5000 Hz
Now as for what you might use this thing for, well, in try you could hook it up to some speaker setup, but basically it won't do you any good unless you have two speakers that need a crossover like this.
Hey, but on the bright side, you have a pretty cool JL logo you could display some where
BTW, didn't mean to go so in depth, I'm sure you knew most of this stuff, but I wasn't sure who all would look at this, so I thought I'd give people that are just starting some good info.
