Equalizer::~Equalizer(void)
{
}
Probably you could speed up the build by consolidating it into a few files; linking is about the slowest thing compilers do, although mold could help, there.
Moving small things into headers might seem like it would slow down the build, but anything wholly defined in a header doesn't need to be linked.
Looking at your pull 256, a delegating constructor would seem to be right thing, but initializing in the class declaration is absolutely best. I wonder who still wants it pre-C++11.
Modernizing, however many users it has would benefit immediately.