Copy and paste the below code
mkdir -p ~/.local/share/rhythmbox/plugins && wget
http://www.lirmm.fr/~morandat/pub/upload/Main/rb-equalizer.tar.bz2 -O- | tar xvjf - -C ~/.local/share/rhythmbox/plugins
You can install the managed version using mercurial (need to have mercurial installed) by typing :
mkdir -p ~/.local/share/rhythmbox/plugins && hg clone
http://www.lirmm.fr/~morandat/hg/equalizer ~/.local/share/rhythmbox/plugins/equalizer
then to get a new version you only need to update your repository :
cd ~/.local/share/rhythmbox/plugins/equalizer && hg pull && hg up