About two years ago we had an article
about a system-wide Pulseaudio equalizer. This tool is still used today but its no longer developed and it doesn't work properly for everyone, so many users have been looking for
Well, I'm not sure if you're aware of this, but Pulseaudio has, for a while, its own built-in system-wide equalizer. However, the Pulseaudio packages available in the official Ubuntu repositories are not build with equalizer support. In Ubuntu 13.04, Pulseaudio is finally build with equalizer support but the actual equalizer is missing from the package for some reason, even though it's available in the source.
So, to make things easier for you, I've create a PPA for Ubuntu 13.04, 12.10 and 12.04 with Pulseaudio built with equalizer support and with the actual equalizer enabled.