Dear @cabkab : There are different type of eq. as graphic or band ones and a blend of it and you need to read information about to look what you need and from different manufacturers which kind of parts devices they use to make the job.
Here is a good explanation on graphic eq. and in the shiit site for band eq.:
https://www.ranecommercial.com/legacy/note101.html
Regards and enjoy the MUSIC NOT DISTORTIONS,
R.