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?
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.
The Real Traps web site provides test tones you can download.
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..
Depending on the placement of your main speakers in the room, you'll get some boundary gain. So the 85 Hz spec may not be meaningful. They must be quite small speakers.

I'd try a) first to see how things sound. Level matching is probably more of an issue with blending the sub with your mains than the crossover.
Nht superzeros...
Hope your sub is more of a woofer than a subwoofer.