Many amplifiers feature built-in crossover filters, bass equalizers among other functions designed to help your installer tune your system to your vehicle acoustics. For instance, if you have 10 cm (4”) speakers installed in your system, which can only reproduce mid and high frequencies, a properly set crossover filter can eliminate the need for them to reproduce low frequencies and will send those speakers only the mid and the high frequencies, vastly improving the proper working of the system while preventing it from damages and from sound distortion. For the subwoofers, crossover filters and bass equalizers are useful tools to balance the low frequency to the rest of the system. Bass equalizers are useful, but remember.... don’t overdo it!