IMO, here is very good stuff :
blogohl: Software and VST plugins
The bidirectional IIR Biquad filter used as crossover guarantees a linear phase:
DSP Robotics Support - Bidirectional IIR filter
Speaker Lab enables flattening the speaker magnitude and phase combining a IIR Biquad filter as Linkwitz Transform in as deep bass equalizer, eight IIR BiQuad filters as general purpose equalizer, and a 128-tap FIR filter as high resolution automatic equalizer in the mids and highs:
DSP Robotics Support - Speaker Lab
Flowstone enables you to mix all techniques in a schematic that you'll save as VST plugin (need a VST-Host for loading the VST plugin), or as plain simple .EXE file to be executed after each boot.
Up to your creativity and taste.
Hardware and software cost close to nihil.
You need to tell Windows XP to route the stereo audio (stereo mixer output) to the VST-ASIO world instead of the soundcard. The VST will take care of the soundcard, provided it operates under ASIO. This is explained here:
DSP Robotics Support - WinXP directly driving two 4-way active speakers
In your lab, you can also rely on Flowstone for measuring the impedance of a speaker driver (it generates a text file):
DSP Robotics Support - Speaker Z Meter
