It is somewhat hard for the beginner to visualize exactly what a crossover is doing. In this section, I have included many frequency response graphs and schematics to help illustrate how a crossover works and what the results are.
Below is a graph of the frequency response of a two-way speaker that happens to be using a Hi-Vi F6 woofer and a Hi-Vi RT2C-A. The four lines show the frequency response of the 2-way combination with different crossover situations.
It can clearly be seen that with no crossover, there is a very large increase in output in the midrange region, and a bright top end. Listening to a speaker in this state would be very fatiguing and grating on the ears, not to mention potentially damaging to the tweeter. Using a standard textbook 2-way crossover at 3000Hz yields improved midrange response; the large peak that remains is partially due to the lack of impedance compensation. Once a conjugate (or Zobel) network is installed, the response improves even more, but there is still a bright top end due to the lack of tweeter padding. Finally, a graph of the response with a customized crossover can be seen. Most likely with the addition of some padding on the tweeter to the textbook crossover with the Zobel network, the response could be made decently flat.
Now that we have seen how the crossover can improve the overall frequency response, we should take a look at what different sections of the crossover do. An attempt shall be made to delve further into an investigation of the custom crossover that I designed for this combination of woofer and tweeter.
Below is a 3-part graph showing the response of the tweeter with various portions of the crossover in use. The top line shows the unmodified response of the tweeter in the enclosure. The second line shows the effect of the high-pass section of the crossover. The lowest line shows the further effects of both the high-pass portion and the L-pad that brings the response down.
Let's take a look at the woofer response:
The top line is the frequency response of the woofer without any type of crossover work. The rise that begins at 500 Hz is a result of the "baffle step" and occurs on all speakers with relatively narrow baffles. In an attempt to correct for this rise, a baffle compensating section was added to the crossover. This lowered the rise by several dB in magnitude. Next, to lower the response output and to remove a lot of the breakup from the response, a second order low-pass circuit is added.
The final combination of the tweeter and woofer and their respective crossovers yields the custom response as seen in the first diagram. Here is a picture of how they sum together.