Hi!
When calculating L-pads for tweeter which impedance should I use:
1. The nominal driver impedance
2. The measured driver impedance around the crossover point.
I use the Vifa DX25TG-05-04 and there is more than 1 Ohm difference betwen the nominal and the real impedeance. (2500Hz)
If I choose the wrong one, than my whole crossover point will slip away, because the wrong L-pad resistor values will change my total tweeter impedance and thereby my used capacitor value will be not correct.
Greets:
Tyimo
When calculating L-pads for tweeter which impedance should I use:
1. The nominal driver impedance
2. The measured driver impedance around the crossover point.
I use the Vifa DX25TG-05-04 and there is more than 1 Ohm difference betwen the nominal and the real impedeance. (2500Hz)
If I choose the wrong one, than my whole crossover point will slip away, because the wrong L-pad resistor values will change my total tweeter impedance and thereby my used capacitor value will be not correct.
Greets:
Tyimo
Actual driver impedance. The nominal is neither here nor there, it's just there to provide a brief / rough guide as to what type of unit it is.
Thank Scott very much!
Is it also true for choosing the capacitor value? I mean to use the actual impedance.
Is it also true for choosing the capacitor value? I mean to use the actual impedance.
Yes indeed. The same applies to all XO components since that's what the filter actually 'sees'. Impedance compensation / flattening may (may) also be necessary depending on the details of the design / what you're hoping to achieve.
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The filter only works as a normal filter if the load is constant.
That requires the speaker impedance to be constant through the passband and for a couple of octaves outside the passband.
A tweeter than changes in impedance from 7ohms to 8ohms is close enough to constant.
A tweeter that changes from 7ohms to 15ohms is far from constant.
The filter is changing as the frequency changes.
This is the main reason that many speakers have speaker Zobels across some of the drivers. To help maintain constant impedance in the passband.
That requires the speaker impedance to be constant through the passband and for a couple of octaves outside the passband.
A tweeter than changes in impedance from 7ohms to 8ohms is close enough to constant.
A tweeter that changes from 7ohms to 15ohms is far from constant.
The filter is changing as the frequency changes.
This is the main reason that many speakers have speaker Zobels across some of the drivers. To help maintain constant impedance in the passband.
Yes.
Of course I need use Zobel to help maintain constant impedance in the passband, but in many design there isn't any Zobel for the tweeter. Only the L-pad.
The qusetion was to use the real impedance value for starting the calculation or the nominal value.
Greets:
Tyimo
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