Design equations, schematic link for the Motown graphic EQ, Altec 9062A graphic EQ

At your risk. This very informative and very recent paper was found with great bibliographic and journal references: Graphic Equalizers Based on Limited Action Netqworks - Kurt James Werner - Proc. 27th International Conference on Digital Audio Effects. If i am not mistaken by reading this paper, the Altec 9062A, Motown EQ are not constant B (constant bandwidth designs), and they are based on simpler constant K, bridged T networks where the varying 2 resistors are part of the LCR (inductor, capacitor, resistor) upper and lower inverse circuits. Also the paper Professional Audio Controls - Artur C. Davis, Don Davis was found by web search and it was realised that Davis are the inventors. Then in the Pleiades lab schematic library a printed patent was found by inventors Artur C. Davis, Donald B. Davis, James J. Noble, (Altec). It is US3624298, Sound Improving Means and Method. It shows in fig. 3 a bridged T constant K network with 2 varying resistors each in the LCR top and bottom inverse circuit. This EQ is an only attenuation version as it is meant for room sound system EQ correction. The inventors describe in detail how it works and the varying Resistors are linear and decrease in oposite directions. Left and right arm resistors are said each to be equal to system impedance. A simpler circuit on this patent, fig 2, is just a variable resistor in parallel with (an inductor in series with a resistor), in parallel with a capacitor. Signal is fed in series with such network. This is very similar to the recently described on euroelectron, fullrange speaker correction crossover network. The inductor in series reduces mid high heaviness, the varying resistor puts back some high frequencies, the capacitor passes higher frequencies if the speaker cannot go very high by itself. Back to the patent, the varying resistor controls increase attenuation bandwidth.