Graphic equalizers in home audio has fallen out of fashion. I don't know of any receiver made now that has them, and separate units seem to be digital parametric types. Many modern receivers have automated room response software that probably does a much better job at room equalization than any of those graphic equalizers.
The problem was that people used those multi-band graphic equalizers as a volume control – as in louder is better. Raising multiple adjacent bands introduced more problems than it solved. Instead of making a smoother frequency response, it made for an uneven noisy one. I used to know a link that explained this problem, but I don't know it. Try reading this instead
Constant-Q Graphic Equalizers.
The conventional variable-Q equalizer suffers from a great deal of filter overlap at low corrective settings (which gives it its "combining" characteristics) and a severe degradation of its bandwidth at high settings, making its performance very unpredictable.
In my experience, using a limited capability digital parametric equalizer built into my receiver, they can be good at taming low frequency room resonance (one note bass). But they should be used to lower responses, not to raise them. And they can only be used well if you have the ability to know what frequencies are the problems. That's where automated room response software is useful.
