Compensation networks are electronic EQ and/or impedance compensation devices. An example is a Zobel circuit, which is used to remove a response peak that would otherwise result from the interaction of capacitance in a passive crossover and the speaker's voice coil. Another example is horn compensation.See the response curve of the tweeter circuit of a π Speaker using a compression horn:
Response curve for HF circuit of π Crossover
For more information, see the links on the post called "A few useful documents."