# calculate crossover with Re or impedance ?

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#### nickthevoice

HI !

When you calculate your crossover you take Impedance or Re ? ...and WHY ?

because the real value when I take mesurement with my multimeter is always equal to Re.

nicK

#### jjrenman

The crossover has to deal with A/C which is an impedence. Your meter is measuring with DC which is resistance. IMO use impedence.

#### AndrewT

the impedance at the crossover frequency is what you require to determine your crossover component values.
The cross over slopes will only be correct if the impedances at the crossover frequency are held flat for at least an octave either side of the crossover frequency and I suspect aiming for two octaves may give audible improvement.

Eg.
crossover frequency is 3kHz.
The 8ohms Bass/Mid driver has an impedance of 9.1ohms @ 3kHz, but is varies from 7.6ohms @ 750Hz to 11ohms @ 12kHz.
You design the crossover for the Bass/Mid for 9.1ohms, but the slope in the impedance either side of 3kHz results in the crossover slopes noy being what is predicted by the model.
T same errors occur for the crossover for the Treble driver.

It is why you see the driver Zobel correction added in so many crossovers.

#### AndrewT

The impedance at the crossover frequency is what you require to determine your crossover component values.
The cross over slopes will only be correct if the impedances at the crossover frequency are held flat for at least an octave either side of the crossover frequency. I suspect aiming for two octaves of flat impedance either side of XO frequency may give audible improvement.

Eg.
crossover frequency is 3kHz.
The 8ohms Bass/Mid driver has an impedance of 9.1ohms @ 3kHz, but it varies from 7.6ohms @ 750Hz, to 11ohms @ 12kHz.
You design the crossover component values for the Bass/Mid of 9.1ohms, but the slope in the impedance either side of 3kHz results in the crossover slopes not being what is predicted by the model.
The same errors occur for the crossover for the Treble driver.

This is why you see the driver Zobel correction added in so many crossovers.

repost with errors corrected

#### nickthevoice

Okay thanks guys !

The best is adding zobel network to keep the impedance always close to the default impedance value ? do you know crossover online calculator how include zobel network ?

By the way I try to cut this tweeter 27TBC/G06 at 2500hz 12dB
(because I had revelation when I listen Totem forest signature at SSI 2013 MTL) wow the sound is amazing !
Normally I hate aluminium tweeter but in this case WOW !