[LAU] Need simple help measuring frequencies

Hi all, I converted the bass track off a midi file to ogg, muting out all the other tracks via timidity. The purpose being I'm about to buy some monitor speakers and I'm deciding what low frequency range is acceptable. I tried audacity and analyze-->plot spectrum, but I can't get that to show me what the low end is doing (I'm sure I'm missing something simple). Anyways, here's a link. What frequency is that bass around? How can I measure that? http://braziloutsource.com/random/carnival_bass.ogg If curious, I'm looking at the m-audio bx8a. I live in a remote place where I can't just walk into a store and demo them, so I have to buy off the internet. Thanks! Robert