In Reply to: Oh Martin, Come on. posted by Bentwrench on May 04, 1999 at 15:33:30:
... So, could you be more specific. I thought I was very direct & candid. In lieu of an explanation as to what you don't understand, I'll explain everything.Zobel corrective circuits try to change the high-frequency (HF) impedence of a dynamic driver, as seen by the cross-over (XO), into a purely resistive load, by counteracting the "Le" (voice-coil inductance) by a proper "Cz" (Zobel capacitor). As the "Le" increases the impedence of the driver, the "Cz" starts to reduce the parallel Zobel circuit impedence to the eventual "Rz" (Zobel resistor) value.
Most all Solid-State (SS) amps are voltage-sources. That means these amplifiers try to dictate the signal's electric potential (as measured in Volts). So, a Zobel circuit mearly helps make the XO work properly. In fact, it may decrease the HF range but so slighltly, it isn't worth considering. This would work by reducing the artificial boost made by using voice-coil reactance increasing the voltage-divider ratio. However minor this amount (< 1dB) is at that HF range several octaves awy from the XO point.
Tubes are current-sources. That means these amplifiers try to dictate the signal's electric current (as measured in Amps). So, while a XO would still act much more appropriately with a Zobel, the Zobel, itself, robs the speaker of the current in HF range by its lower impedence. Maybe you've heard of the over-used addige that "current seeks the path of least resistance". This happens in a SS too, but unlike a SS, the tube doesn't supply extra current for the lowered impedence.
Hope this helps...
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