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Output transformer question

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Trooper: To clarify, you are measuring DC resistance with your meter. Your meter has an internal battery to apply a small DC current to the speaker (or resistor or whatever) to give you a resistance value at DC (abbreviated DCR).

Impedance is this resistance at various AC frequencies, not at DC. Speaker driver voice coils are inductors, and if you have multiway speakers the crossovers have inductors, resistors and caps. The inductor's and capacitor's resistances change with frequency. Resistors "resistance" does change with frequency.

So a typical speaker has an "impedance plot" of resistance vs freq. Some are fairly flat across the frequency spectrum and others are not. Flat impedance speakers usually play well with no-feedback tube amps since no feedback amp's output impedance is relatively high.

As mentioned, typical 8 ohm impedance speakers usually measure around 6-7 ohms DCR.
 
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