fixed crossover setting...sub pre out

Have older Sherwood rd 6500 ave with sub pre out....although the manual doesn't specify a crossover had small or large speaker settings...should I assume do I know?
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Measure it?
You can get an inexpensive SPL meter at a Radio Shak and buy a test record or CD wich has the frequencies on separate tracks. That is one way to measure it.
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thanks guys...I contacted Sherwood and Parts express...both quickly confirmed 80hz...which leaves me in a dilemna...the crossover in the RD 6500 is non-defeatable...however...i would like to crossover my mains are rated to 85hz(3db down)...should I a)be not concerned, b)set the crossover on my sub to whatever I want which isnt ideal, or c)throw the Sherwood out the window...haha..
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Nht superzeros...
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