[LAU] Implementing a crossover with ladspa plugins?

[S. Massy]

Hello, all,
Here's a question for the fine DSP and accoustic experts on this list. I
need to apply different processing (mostly reverb and compression) to
different bandwidths of the frequency spectrum on a given track. How
would I go about using filters to implement crossovers as flat as
possible? Most plugins do not actually seem to tell what their rolloff
curve is. 
Thanks.
Cheers,
s.M.

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