Sound Analyzer

I'm curious to compare my computer speakers performance to what is being sent out by my computer. Does anyone know of a frequency analyzer for computers? Not something for adjusting the EQ (but it could also do that). What I'd like to see is basically the output frequencies and sound level prior to my speakers outputting them regardless of what is causing the sound. That way I can compare how my speakers are performing to see if I need new ones or not. This is especially important to me at the low frequencies. I could also use that to adjust my speakers to a true output balance of treble and bass. Essentially FRAPS for sound I guess is what I'm looking for.