Same problem. It does not work.

confirmed, dont work...confirmed in Fedora 19 with latest updates and Rhythmbox 2.99.1

This message is a reminder that Fedora 18 is nearing its end of life.
Approximately 4 (four) weeks from now Fedora will stop maintaining
and issuing updates for Fedora 18. It is Fedora's policy to close all
bug reports from releases that are no longer maintained. At that time
this bug will be closed as WONTFIX if it remains open with a Fedora 
'version' of '18'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version' 
to a later Fedora version prior to Fedora 18's end of life.

Thank you for reporting this issue and we are sorry that we may not be 
able to fix it before Fedora 18 is end of life. If you would still like 
to see this bug fixed and are able to reproduce it against a later version 
of Fedora, you are encouraged  change the 'version' to a later Fedora 
version prior to Fedora 18's end of life.

Although we aim to fix as many bugs as possible during every release's 
lifetime, sometimes those efforts are overtaken by events. Often a 
more recent Fedora release includes newer upstream software that fixes 
bugs or makes them obsolete.

Same problem with Fedora 20:

rhythmbox-3.0.1-3.fc20.x86_64
rhythmbox-equalizer-1.4-6.fc20.x86_64

It seems this problem exists since a long time.

If rhythmbox-equalizer is no longer compatible with rhythmbox it should be remove from repo.

So, here we go again...
This issue exists since Fedora 17, as you can find out if you search for "Rhythmbox equalize".

So, who is responsible for mantainance of plugins?

If it DOES NOT work, so please don't make it available in the repository.

This shows, that things get systematically released, without any care on testing.

Fedora 18 changed to end-of-life (EOL) status on 2014-01-14. Fedora 18 is
no longer maintained, which means that it will not receive any further
security or bug fix updates. As a result we are closing this bug.

If you can reproduce this bug against a currently maintained version of
Fedora please feel free to reopen this bug against that version. If you
are unable to reopen this bug, please file a new report against the
current release. If you experience problems, please add a comment to this
bug.

Thank you for reporting this bug and we are sorry it could not be fixed.

Hey! So what?

The plug-in can be found even in the Fedora repository for Fedora20...

PLEASE, MAKE THE plugin-PACKAGE IN FEDORA-REPOS UNAVAILABLE !!!