I think all music and audio voice recordings play through a media player. The equalizing would have to be done within that player. When Safari appears to be playing music, it's actually being played by a media player, probably iTunes or Quicktime. I happen to use VLC. You can universally change the media player app used for various types of media files by right clicking on one of those files, selecting "Get Info," then selecting the desired media player in the Open With list and clicking on "Change All." I've elected to Change All to VLC and Safari uses VLC when playing media files. You have to specify the selection for each type of media file. I think most media players incorporate a basic equalizer, I know that VLC does.
