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Typically horn flare rates (areas)are described by the term "cut-off" frequency aka "Fc"; at freques below this this the horn just about stops working. You put Fc into the exponential equation however, PWK often used the term "lamedh" (I'll use "Ld") to describe the horn area expansion; It is the lengh of travel down the horn in which the area doubles (or halves). Therefor the expansion works like animals / bacterium doubling every time period. If my math is correct, the cuttoff wavelength (I'll call it "Lc) is 18.1 times the length to double. We can examine the LaScala's two paths (combined) and notice the area at the throat is 0.5 ft^2; then the paths go across the back to the interior corners where the area is 1 ft^2; then toward the front for a foot to where the area is 2 ft^2; then another foot to the mouth where the combined area is 4 ft^2. Therefore we see the Ld is 1 foot or 12 inches. The Lc is thus 18.1 * 12 and we dived the velocity of sound 15,00 in/sec by that wavelength to get an Fc of 62 Hz. We can check the PWK article on the K400 horn and notice that the length to double is given as 2.75 inches. The math like the above shows that it's Fc is 270 Hz. PWK was really getting it to go as low as possible to where the bass bin on the Khorn is running out of steam! Good night all, WMcD
