Passive crossover network installed in your speaker box have several problem. They dissipate the audio power, therefore it’s not environmentally friendly. Thus, the inductor and capacitor inside the passive crossover network contribute the signal distortion due to low impedance load of the loudspeaker. To overcome, the best way to get high quality audio is to separate the high and low frequencies before feeding the signal to the amplifier. To amplify the low and high audio signal, two amplifiers is needed. Here is the circuit diagram :
The circuit use a constant voltage method, means that the output of high and low frequency is summed up, and then fed back to be compared with the input to make sure this sum is equal to the input signal. This method ensure that the total response is flat, if we summed back the separated high and low frequency output. (Source : National Semiconductor Application Notes)
You have to use 1% tolerance for the resistors to give a precise response. According to the formula, the capacitor C should be 6.6nF to give 1kHz crossover frequency, but a 6.8nF can be used because it waidely available, and the crossover frequency will be shifted to about 975Hz.