Remember Even a modest 3 decibels of change is very significant to the human ear. Extreme differences in the frequency response pattern of a nominally flat system will sound stilted and unnatural. It is virtually impossible to reproduce the complex timbre of music in exactly the way it was created in the recording studio. Every loudspeaker is a unique instrument of reproduction that is inherently incapable of reproducing every part of the sound spectrum with equal intensity. In multiple speaker systems, things are even more complex because different drivers interact with each other.
Equalizers offer the capability of both compensating for defects and fine tuning the system.
With an equalizer, certain frequency ranges can be either increased or cut, to shape the overall sound spectrum to compensate for defects in the original soundscape, or to bring out certain instruments, or simply as an expression of the listener's preference. Electronically, the equalizer is situated on the line feed between the receiver and the amplifier. Because it modifies low level high impedance signals only, it is less vulnerable to electrical overloads than the amplifier, and is overall less likely than either the receiver, or the amp to create problems. The number of bands in an equalizer control how finely the frequency pattern can be amplified or attenuated. Three to 30 bands or more, can be provided by available equipment.