Beginner's capacitor question

[Jim Leonard]

I have a need to record the output of a (5150) speaker.  Although I 
thought that I could just alligator-clip a positive lead to one speaker 
terminal and the negative to the case/ground, the output was decidedly 
"buzzy" (I assumed it was too "hot" and overmodulating).  I routed it 
into a mixer and turned it down (speaker is 5v, not sure what line input 
is) but it still didn't sound right.

I found some old directions on hooking up a PC speaker to a line input, 
and was confused by the use of a capacitor -- I would have thought that 
a resistor would have been more appropriate, to limit the signal 
perhaps?  In any case, here are the instructions, followed by my question:

Parts required:
- 6' to 12' shielded cable with RCA plug (male) on one end
- Two alligator clips
- One 4.7 uf capacitor

1. Connect one alligator clip to the shielded portion of the cable.
2. Connect the (-) minus side of the capacitor to the center conductor 
of the cable and then connect the (+) side of the capacitor to the 
second alligator clip.
3. Attach the clip with the capacitor to one of the wires going to your 
computer's speaker.  Attach the other clip to the metal case (ground) 
somewhere (such as a screw or bolt connection).
4. Connect the RCA plug to the auxiliary input on your stereo system or 
boom box.

While I have read the wikipedia entry on capacitors, I'm missing 
something obvious.  My question:  Why the 4.7uf capacitor?  Does it 
serve to limit the signal?  Reduce it's voltage?  (or increase it?) 
Filter the signal in some way?
-- 
Jim Leonard (trixter at oldskool.org)            http://www.oldskool.org/
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