Conclusion
    This has been more of a philosophic article than a how-to article. Asides from the balance and width control and phase control, these sonic controls must be invented. Unfortunately, since 99.99% of the professional audio amplifier designer's research time is spent on how to reduce amplifier distortion from 0.0003 to 0.0001% and the golden eared are proudly non-technical, we do not have a vast body of research to fall back on. It is sad to reflect on early death of Alan Blumlein, the brilliant inventor stereo. He patented stereo in 1933 and he had an amazingly deep understanding of the principles underlying the actual perception of an acoustic event. For example, he knew that the pan-pot approach used in all modern recording studios is inadequate to the task of moving the perceived position of a sound without smearing the sound, as there must also be a frequency selective compensation. No doubt, had he lived into the end of the last century, all our stereos would sound much better as a result. In his absence, we will have to carry on his work.
                                //JRB

Further Readings
     
"Alan Dower Blumlein," Robert Alexander, Electronics World, Mar. 2000

"Improving Stereo Image Sharpness," F.O. Edeko, Electronics World, Jan. 1988

"Image Movement in Stereophonic Sound Systems," F.O. Edeko, Electronics World, Oct. 1988

"Improve Your Image," Richard Brice, Electronics World, Oct. 1998

"Stereo from All Angles I," John Watkinson, Electronics World, July 1999

"Stereo from All Angles II," John Watkinson, Electronics World, Aug. 1999

"Stereo from All Angles III," John Watkinson, Electronics World, Nov. 1999

"Stereo from All Angles IV," John Watkinson, Electronics World, Jan. 2000

"Stereo from All Angles V," John Watkinson, Electronics World, Mar. 2000

  The first
  Tube CAD Journal
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TCJ Filter Designer lets you design a filter or crossover (passive, solid-state or tube) without having to check out thick textbooks from the library and without having to breakout the scientific calculator. This program's goal is to provide a quick and easy display not only of the frequency response, but also of the resistor and capacitor values for a passive and active filters and crossovers. Tube crossovers are a major part of this program; both buffered and unbuffered tube based filters along with mono-polar and bipolar power supply topologies are covered.   

For more information, read the article "Tube-Based Crossovers" in the Tube CAD Journal.
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