Frequency response of my two way speakers, Graetz typ.5400(Isophon P2132 equiv.) and Siemens 6 Ruf lsp 28a, 6dB/oct network at 2.5kHz. Ignore red plot, see background gray plot. Gray represents peak level sweep from 20Hz to 20kHz. Connected the sine wave generator to the amplifier, sweeped from 20Hz to 20kHz and measured by iPhone Sonic Tools APP. Definitely, I need to do something on the dimple @