Rusty Boudreaux wrote:

A typical preamp/receiver has a 2nd order 12dB per octave high
pass crossover for speakers set to 'small'. The subwoofer output
has a 4th order 24dB per octave low pass filter.

So, if you set your crossover at 80Hz:

the subwoofer output will be attenuated
24dB at 160Hz
48dB at 320Hz
96dB at 640Hz, etc

the 'small' speaker will be attenuated
12dB at 40Hz
24dB at 20Hz
48dB at 10Hz

Note, this is the attenuation of the speaker electrical input not
the speaker output. The speaker may have additional rolloff of
it's own. For example, a typical surround speaker will have
insignificant output below 20-40Hz even when driven by a full
range signal. So the total attenuation is much higher than just
the crossover.

Thanks. That's exactly what I needed.