Is it compulsory to install the crossover supplied?

You should always be vigilant during installation, check how all components of your audio system are connected to each other before commissioning the system. Supplied crossovers (cable crossovers & cabinet crossovers) should always be installed in partially active mode. Especially with tweeters, a filtering of the frequency band is mandatory, make sure that you either have an active filter in the amplifier / headunit / DSP active or use the supplied crossover!